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1
Sedlmayr, Martin, Tobias Würfl, Christian Maier, Lothar Häberle, Peter Fasching, Hans-Ulrich Prokosch, and Jan Christoph. "Optimizing R with SparkR on a commodity cluster for biomedical research." Computer Methods and Programs in Biomedicine 137 (December 2016): 321–28. http://dx.doi.org/10.1016/j.cmpb.2016.10.006.
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Chang, Bao Rong, Yun-Da Lee, and Po-Hao Liao. "Development of Multiple Big Data Analytics Platforms with Rapid Response." Scientific Programming 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/6972461.
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The crucial problem of the integration of multiple platforms is how to adapt for their own computing features so as to execute the assignments most efficiently and gain the best outcome. This paper introduced the new approaches to big data platform, RHhadoop and SparkR, and integrated them to form a high-performance big data analytics with multiple platforms as part of business intelligence (BI) to carry out rapid data retrieval and analytics with R programming. This paper aims to develop the optimization for job scheduling using MSHEFT algorithm and implement the optimized platform selection based on computing features for improving the system throughput significantly. In addition, users would simply give R commands rather than run Java or Scala program to perform the data retrieval and analytics in the proposed platforms. As a result, according to performance index calculated for various methods, although the optimized platform selection can reduce the execution time for the data retrieval and analytics significantly, furthermore scheduling optimization definitely increases the system efficiency a lot.
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Saka, Chika, Tomoki Oshika, and Masayuki Jimichi. "Visualization of tax avoidance and tax rate convergence." Meditari Accountancy Research 27, no. 5 (October 7, 2019): 695–724. http://dx.doi.org/10.1108/medar-02-2018-0298.
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Purpose This study aims to explore the evidence of the probability of firms’ tax avoidance and the downward convergence trend of national statutory tax rates and firms’ effective tax rates. Design/methodology/approach This research employs exploratory data analysis using interactive data manipulation and visualization tools, namely, R with SparkR, dplyr, ggplot2 and googleVis (GeoChart and Motion Chart) packages. This analysis is based on the world-scale accounting data of all listed firms from 148 countries spanning 30 years. Findings The results reveal the following: three types of evidences on probability of firms’ tax avoidance, showing a non-random distribution of firms’ effective tax rates and return on assets, cross-sectional variation of firms’ effective tax rates in each country, and the trend of difference between effective tax rates and statutory tax rates, and the downward convergence trend of statutory tax rates and firms’ effective tax rates. Practical implications The results highlight the prominent issues of world-scale tax avoidance and tax rate competition and facilitate a collaborative discussion between laymen and professionals using objective evidence. Originality/value A novel methodology is adopted through the visualization of world-scale accounting data, which can facilitate a new perspective, revealing unexpected patterns and trends in otherwise hidden information. This study also highlights the importance of global consideration of firms’ tax avoidance and tax rate competition, using objective evidence.
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Laasmaa, Martin, Niina Karro, Rikke Birkedal, and Marko Vendelin. "IOCBIO Sparks detection and analysis software." PeerJ 7 (March 29, 2019): e6652. http://dx.doi.org/10.7717/peerj.6652.
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Analysis of calcium sparks in cardiomyocytes can provide valuable information about functional changes of calcium handling in health and disease. As a part of the calcium sparks analysis, sparks detection and characterization is necessary. Here, we describe a new open-source platform for automatic calcium sparks detection from line scan confocal images. The developed software is tailored for detecting only calcium sparks, allowing us to design a graphical user interface specifically for this task. The software enables detecting sparks automatically as well as adding, removing, or adjusting regions of interest marking each spark. The results of the analysis are stored in an SQL database, allowing simple integration with statistical tools. We have analyzed the performance of the algorithm using a large set of synthetic images with varying spark sizes and noise levels and also compared the analysis results with results obtained by software established in the field. The use of our software is illustrated by an analysis of the effect of isoprenaline (ISO) on spark frequency, amplitude, and spatial and temporal characteristics. For that, cardiomyocytes from C57BL/6 mice were used. We demonstrated an increase in spark frequency, tendency of having larger spark amplitudes, sparks with a longer duration, and occurrence of multiple sparks from the same site in the presence of ISO. We also show that the duration and the width of sparks with the same amplitude were similar in the absence and presence of ISO. The software was released as an open source repository and is available for free use and collaborative development.
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Bao, Rongfeng, Lawrence M. Lifshitz, Richard A. Tuft, Karl Bellvé, Kevin E. Fogarty, and Ronghua ZhuGe. "A Close Association of RyRs with Highly Dense Clusters of Ca2+-activated Cl− Channels Underlies the Activation of STICs by Ca2+ Sparks in Mouse Airway Smooth Muscle." Journal of General Physiology 132, no. 1 (June 30, 2008): 145–60. http://dx.doi.org/10.1085/jgp.200709933.
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Ca2+ sparks are highly localized, transient releases of Ca2+ from sarcoplasmic reticulum through ryanodine receptors (RyRs). In smooth muscle, Ca2+ sparks trigger spontaneous transient outward currents (STOCs) by opening nearby clusters of large-conductance Ca2+-activated K+ channels, and also gate Ca2+-activated Cl− (Cl(Ca)) channels to induce spontaneous transient inward currents (STICs). While the molecular mechanisms underlying the activation of STOCs by Ca2+ sparks is well understood, little information is available on how Ca2+ sparks activate STICs. In the present study, we investigated the spatial organization of RyRs and Cl(Ca) channels in spark sites in airway myocytes from mouse. Ca2+ sparks and STICs were simultaneously recorded, respectively, with high-speed, widefield digital microscopy and whole-cell patch-clamp. An image-based approach was applied to measure the Ca2+ current underlying a Ca2+ spark (ICa(spark)), with an appropriate correction for endogenous fixed Ca2+ buffer, which was characterized by flash photolysis of NPEGTA. We found that ICa(spark) rises to a peak in 9 ms and decays with a single exponential with a time constant of 12 ms, suggesting that Ca2+ sparks result from the nonsimultaneous opening and closure of multiple RyRs. The onset of the STIC lags the onset of the ICa(spark) by less than 3 ms, and its rising phase matches the duration of the ICa(spark). We further determined that Cl(Ca) channels on average are exposed to a [Ca2+] of 2.4 μM or greater during Ca2+ sparks. The area of the plasma membrane reaching this level is <600 nm in radius, as revealed by the spatiotemporal profile of [Ca2+] produced by a reaction-diffusion simulation with measured ICa(spark). Finally we estimated that the number of Cl(Ca) channels localized in Ca2+ spark sites could account for all the Cl(Ca) channels in the entire cell. Taken together these results lead us to propose a model in which RyRs and Cl(Ca) channels in Ca2+ spark sites localize near to each other, and, moreover, Cl(Ca) channels concentrate in an area with a radius of ∼600 nm, where their density reaches as high as 300 channels/μm2. This model reveals that Cl(Ca) channels are tightly controlled by Ca2+ sparks via local Ca2+ signaling.
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Kou, Jie, Xinman Zhang, Yuxuan Huang, and Cong Zhang. "SAVSDN: A Scene-Aware Video Spark Detection Network for Aero Engine Intelligent Test." Sensors 21, no. 13 (June 29, 2021): 4453. http://dx.doi.org/10.3390/s21134453.
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Due to carbon deposits, lean flames, or damaged metal parts, sparks can occur in aero engine chambers. At present, the detection of such sparks deeply depends on laborious manual work. Considering that interference has the same features as sparks, almost all existing object detectors cannot replace humans in carrying out high-precision spark detection. In this paper, we propose a scene-aware spark detection network, consisting of an information fusion-based cascading video codec-image object detector structure, which we name SAVSDN. Unlike video object detectors utilizing candidate boxes from adjacent frames to assist in the current prediction, we find that efforts should be made to extract the spatio-temporal features of adjacent frames to reduce over-detection. Visualization experiments show that SAVSDN can learn the difference in spatio-temporal features between sparks and interference. To solve the problem of a lack of aero engine anomalous spark data, we introduce a method to generate simulated spark images based on the Gaussian function. In addition, we publish the first simulated aero engine spark data set, which we name SAES. In our experiments, SAVSDN far outperformed state-of-the-art detection models for spark detection in terms of five metrics.
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Picht, Eckard, Aleksey V. Zima, Lothar A. Blatter, and Donald M. Bers. "SparkMaster: automated calcium spark analysis with ImageJ." American Journal of Physiology-Cell Physiology 293, no. 3 (September 2007): C1073—C1081. http://dx.doi.org/10.1152/ajpcell.00586.2006.
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Ca sparks are elementary Ca-release events from intracellular Ca stores that are observed in virtually all types of muscle. Typically, Ca sparks are measured in the line-scan mode with confocal laser-scanning microscopes, yielding two-dimensional images (distance vs. time). The manual analysis of these images is time consuming and prone to errors as well as investigator bias. Therefore, we developed SparkMaster, an automated analysis program that allows rapid and reliable spark analysis. The underlying analysis algorithm is adapted from the threshold-based standard method of spark analysis developed by Cheng et al. ( Biophys J 76: 606–617, 1999) and is implemented here in the freely available image-processing software ImageJ. SparkMaster offers a graphical user interface through which all analysis parameters and output options are selected. The analysis includes general image parameters (number of detected sparks, spark frequency) and individual spark parameters (amplitude, full width at half-maximum amplitude, full duration at half-maximum amplitude, full width, full duration, time to peak, maximum steepness of spark upstroke, time constant of spark decay). We validated the algorithm using images with synthetic sparks embedded into backgrounds with different signal-to-noise ratios to determine an analysis criteria at which a high sensitivity is combined with a low frequency of false-positive detections. Finally, we applied SparkMaster to analyze experimental data of sparks measured in intact and permeabilized ventricular cardiomyocytes, permeabilized mammalian skeletal muscle, and intact smooth muscle cells. We found that SparkMaster provides a reliable, easy to use, and fast way of analyzing Ca sparks in a wide variety of experimental conditions.
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Herrera, Gerald M., Thomas J. Heppner, and Mark T. Nelson. "Voltage dependence of the coupling of Ca2+ sparks to BKCa channels in urinary bladder smooth muscle." American Journal of Physiology-Cell Physiology 280, no. 3 (March 1, 2001): C481—C490. http://dx.doi.org/10.1152/ajpcell.2001.280.3.c481.
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Large-conductance Ca2+-dependent K+(BKCa) channels play a critical role in regulating urinary bladder smooth muscle (UBSM) excitability and contractility. Measurements of BKCa currents and intracellular Ca2+ revealed that BKCa currents are activated by Ca2+ release events (Ca2+ sparks) from ryanodine receptors (RyRs) in the sarcoplasmic reticulum. The goals of this project were to characterize Ca2+ sparks and BKCa currents and to determine the voltage dependence of the coupling of RyRs (Ca2+ sparks) to BKCachannels in UBSM. Ca2+ sparks in UBSM had properties similar to those described in arterial smooth muscle. Most Ca2+ sparks caused BKCa currents at all voltages tested, consistent with the BKCa channels sensing ∼10 μM Ca2+. Membrane potential depolarization from −50 to −20 mV increased Ca2+ spark and BKCacurrent frequency threefold. However, membrane depolarization over this range had a differential effect on spark and current amplitude, with Ca2+ spark amplitude increasing by only 30% and BKCa current amplitude increasing 16-fold. A major component of the amplitude modulation of spark-activated BKCa current was quantitatively explained by the known voltage dependence of the Ca2+ sensitivity of BKCa channels. We, therefore, propose that membrane potential, or any other agent that modulates the Ca2+sensitivity of BKCa channels, profoundly alters the coupling strength of Ca2+ sparks to BKCa channels.
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Stern, Michael D., Eduardo Ríos, and Victor A. Maltsev. "Life and death of a cardiac calcium spark." Journal of General Physiology 142, no. 3 (August 26, 2013): 257–74. http://dx.doi.org/10.1085/jgp.201311034.
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Calcium sparks in cardiac myocytes are brief, localized calcium releases from the sarcoplasmic reticulum (SR) believed to be caused by locally regenerative calcium-induced calcium release (CICR) via couplons, clusters of ryanodine receptors (RyRs). How such regeneration is terminated is uncertain. We performed numerical simulations of an idealized stochastic model of spark production, assuming a RyR gating scheme with only two states (open and closed). Local depletion of calcium in the SR was inevitable during a spark, and this could terminate sparks by interrupting CICR, with or without assumed modulation of RyR gating by SR lumenal calcium. Spark termination by local SR depletion was not robust: under some conditions, sparks could be greatly and variably prolonged, terminating by stochastic attrition–a phenomenon we dub “spark metastability.” Spark fluorescence rise time was not a good surrogate for the duration of calcium release. Using a highly simplified, deterministic model of the dynamics of a couplon, we show that spark metastability depends on the kinetic relationship of RyR gating and junctional SR refilling rates. The conditions for spark metastability resemble those produced by known mutations of RyR2 and CASQ2 that cause life-threatening triggered arrhythmias, and spark metastability may be mitigated by altering the kinetics of the RyR in a manner similar to the effects of drugs known to prevent those arrhythmias. The model was unable to explain the distributions of spark amplitudes and rise times seen in chemically skinned cat atrial myocytes, suggesting that such sparks may be more complex events involving heterogeneity of couplons or local propagation among sub-clusters of RyRs.
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Zhou, J., G. Brum, A. González, B. S. Launikonis, M. D. Stern, and E. Ríos. "Ca2+ Sparks and Embers of Mammalian Muscle. Properties of the Sources." Journal of General Physiology 122, no. 1 (June 30, 2003): 95–114. http://dx.doi.org/10.1085/jgp.200308796.
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Ca2+ sparks of membrane-permeabilized rat muscle cells were analyzed to derive properties of their sources. Most events identified in longitudinal confocal line scans looked like sparks, but 23% (1,000 out of 4,300) were followed by long-lasting embers. Some were preceded by embers, and 48 were “lone embers.” Average spatial width was ∼2 μm in the rat and 1.5 μm in frog events in analogous solutions. Amplitudes were 33% smaller and rise times 50% greater in the rat. Differences were highly significant. The greater spatial width was not a consequence of greater open time of the rat source, and was greatest at the shortest rise times, suggesting a wider Ca2+ source. In the rat, but not the frog, spark width was greater in scans transversal to the fiber axis. These features suggested that rat spark sources were elongated transversally. Ca2+ release was calculated in averages of sparks with long embers. Release current during the averaged ember started at 3 or 7 pA (depending on assumptions), whereas in lone embers it was 0.7 or 1.3 pA, which suggests that embers that trail sparks start with five open channels. Analysis of a spark with leading ember yielded a current ratio ranging from 37 to 160 in spark and ember, as if 37–160 channels opened in the spark. In simulations, 25–60 pA of Ca2+ current exiting a point source was required to reproduce frog sparks. 130 pA, exiting a cylindric source of 3 μm, qualitatively reproduced rat sparks. In conclusion, sparks of rat muscle require a greater current than frog sparks, exiting a source elongated transversally to the fiber axis, constituted by 35–260 channels. Not infrequently, a few of those remain open and produce the trailing ember.
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Ferrier, Gregory R., Robin H. Smith, and Susan E. Howlett. "Calcium sparks in mouse ventricular myocytes at physiological temperature." American Journal of Physiology-Heart and Circulatory Physiology 285, no. 4 (October 2003): H1495—H1505. http://dx.doi.org/10.1152/ajpheart.00802.2002.
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In cardiac muscle, Ca2+ is released from the sarcoplasmic reticulum (SR) in units called Ca2+ sparks. Ca2+ spark characteristics have been studied almost entirely at room temperature. This study compares characteristics of spontaneous sparks detected with fluo 3 in resting mouse ventricular myocytes at 22 and 37°C. The incidence and frequency of Ca2+ sparks decreased dramatically at 37°C compared with 22°C. Also, spark amplitudes and times to peak were significantly reduced at 37°C. In contrast, spatial width and decay times were unchanged. During field stimulation, peak spatially averaged transients were similar at 22 and 37°C, and experiments with fura 2 demonstrated that diastolic and systolic Ca2+ concentrations were unchanged. However, SR Ca2+ content decreased significantly at 37°C. Restoration of SR Ca2+ by superfusion with 5 mM Ca2+ increased spark frequency but did not reverse the effects of temperature on spark parameters. Thus effects of temperature on spark frequency may reflect changes in SR stores, whereas changes in spark amplitude and rise time may reflect known effects of temperature on ryanodine receptor function.
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Lacampagne, Alain, Christopher W. Ward, Michael G. Klein, and Martin F. Schneider. "Time Course of Individual Ca2+ Sparks in Frog Skeletal Muscle Recorded at High Time Resolution." Journal of General Physiology 113, no. 2 (February 1, 1999): 187–98. http://dx.doi.org/10.1085/jgp.113.2.187.
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Discrete Ca2+ release events (Ca2+ “sparks”) were recorded in cut segments of single frog skeletal muscle fibers using a video-rate laser-scanning confocal microscope operating in line-scan mode (63 μs per line). Fibers loaded with the Ca2+ indicator fluo-3 were voltage clamped at a holding potential of 0 mV, briefly reprimed at −90 mV, and then strongly depolarized with a large test pulse to activate any reprimed voltage sensors. Using this high time resolution system, it was possible to record individual Ca2+ sparks at ∼30-fold higher time resolution than previously attained. The resulting new experimental data provides a means of characterizing the time course of fluorescence during the brief (a few milliseconds) rising phase of a spark, which was not possible with the previously used 1.5–2 ms per line confocal systems. Analysis of the time course of individual identified events indicates that fluorescence begins to rise rather abruptly at the start of the spark, continues to rise at a slightly decreasing rate to a relatively sharp peak, and then declines along a quasi-exponential time course. The mean rise time of 198 sparks was 4.7 ± 0.1 ms, and there was no correlation between rise time and peak amplitude. Average sparks constructed by temporally and spatially superimposing and summing groups of individual sparks having similar rise times gave a lower noise representation of the sparks, consistent with the time course of individual events. In theory, the rising phase of a spark provides a lower bound estimation of the time that Ca2+ ions are being released by the sarcoplasmic reticulum Ca2+ channel(s) generating the spark. The observed time course of fluorescence suggests that the Ca2+ release underlying a spark could continue at a fairly constant rate throughout the rising phase of the spark, and then stop rather abruptly at the time of the peak.
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Satoh, H., L. A. Blatter, and D. M. Bers. "Effects of [Ca2+]i, SR Ca2+ load, and rest on Ca2+ spark frequency in ventricular myocytes." American Journal of Physiology-Heart and Circulatory Physiology 272, no. 2 (February 1, 1997): H657—H668. http://dx.doi.org/10.1152/ajpheart.1997.272.2.h657.
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In heart, spontaneous local increases in cytosolic Ca2+ concentration ([Ca2+]i) called "Ca2+ sparks" may be fundamental events underlying both excitation-contraction coupling and resting Ca2+ leak from the sarcoplasmic reticulum (SR). In this study, resting Ca2+ sparks were analyzed in rabbit and rat ventricular myocytes with laser scanning confocal microscopy and the fluorescent Ca2+ indicator fluo 3. During the first 20 s of rest after regular electrical stimulation, both the frequency of Ca2+ sparks and SR Ca2+ content gradually decreased in rabbit. When rabbit SR Ca2+ content was decreased by reduction of stimulation rate. the initial resting spark frequency was also decreased, even though resting [Ca2+]i was unchanged. The rest-dependent decrease in spark frequency in rabbit cells was prevented by inhibition of Na+/Ca2+ exchange (which also prevents SR Ca2+ depletion during rest). These results suggest that elevation of SR Ca2+ content can increase Ca2+ spark frequency. In contrast to rabbit cells, 20 s of rest produced a gradual increase in spark frequency in rat cells, although SR Ca2+ content was constant and Ca2+ influx was completely prevented. This indicates that there is a time-dependent increase in spark probability during rest that is independent of [Ca2+]i or SR Ca2+. This effect was also apparent in rabbit cells when SR Ca2+ depletion was prevented by blocking Na+/Ca2+ exchange. Stimulation of Ca2+ extrusion via Na+/Ca2+ exchange in the rat (by Ca2+-free superfusion, which slowly depletes SR Ca2+ content) converted the normal rest-dependent increase in spark frequency to a decrease. The amplitude of individual Ca2+ sparks increased with increasing SR Ca2+ content. In the Ca2+-overloaded state, fusion of sparks or long-lasting localized increases of [Ca2+]i were observed with increased spark frequency. We conclude that the resting frequency of Ca2+ sparks can be independently affected by changes in SR Ca2+ content, [Ca2+]i, or rest period. The latter may reflect recovery of the SR Ca2+ release channels from inactivation or adaptation.
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Eckhoff, Rolf K. "Ignition of Combustible Dust Clouds by Strong Capacitive Electric Sparks of Short Discharge Times." Zeitschrift für Physikalische Chemie 231, no. 10 (October 26, 2017): 1683–707. http://dx.doi.org/10.1515/zpch-2016-0935.
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Abstract It has been known for more than half a century that the discharge times of capacitive electric sparks can influence the minimum ignition energies of dust clouds substantially. Experiments by various workers have shown that net electric-spark energies for igniting explosive dust clouds in air were reduced by a factor of the order of 100 when spark discharge times were increased from a few μs to 0.1–1 ms. Experiments have also shown that the disturbance of the dust cloud by the shock/blast wave emitted by “short” spark discharges is a likely reason for this. The disturbance increases with increasing spark energy. In this paper a hitherto unpublished comprehensive study of this problem is presented. The work was performed about 50 years ago, using sparks of comparatively high energies (strong sparks). Lycopodium was used as test dust. The experiments were conducted in a brass vessel of 1 L volume. A transient dust cloud was generated in the vessel by a blast of compressed air. Synchronization of appearance of dust cloud and spark discharge was obtained by breaking the spark gap down by the dust cloud itself. This may in fact also be one possible synchronization mechanism in accidental industrial dust explosions initiated by electrostatic sparks. The experimental results for various spark energies were expressed as the probability of ignition, based on 100 replicate experiments, as a function of the nominal dust concentration. All probabilities obtained were 0%<p<100%. A tentative mathematical model could be fitted to all the data, assuming that the life time of the spark channel as an effective ignition source increased with the spark energy, that the minimum time of contact between the spark and the dust cloud for ignition to occur was a function of spark energy and nominal dust concentration, and that the stochastic element was the statistical distribution of the time interval between spark appearance and re-establishment of contact between spark channel and dust cloud, following detachment of the dust cloud from the spark by the shock/blast wave emitted by the spark discharge.
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ZhuGe, Ronghua, Kevin E. Fogarty, Stephen P. Baker, John G. McCarron, Richard A. Tuft, Lawrence M. Lifshitz, and John V. Walsh. "Ca2+ spark sites in smooth muscle cells are numerous and differ in number of ryanodine receptors, large-conductance K+ channels, and coupling ratio between them." American Journal of Physiology-Cell Physiology 287, no. 6 (December 2004): C1577—C1588. http://dx.doi.org/10.1152/ajpcell.00153.2004.
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Ca2+ sparks are highly localized Ca2+ transients caused by Ca2+ release from sarcoplasmic reticulum through ryanodine receptors (RyR). In smooth muscle, Ca2+ sparks activate nearby large-conductance, Ca2+-sensitive K+ (BK) channels to generate spontaneous transient outward currents (STOC). The properties of individual sites that give rise to Ca2+ sparks have not been examined systematically. We have characterized individual sites in amphibian gastric smooth muscle cells with simultaneous high-speed imaging of Ca2+ sparks using wide-field digital microscopy and patch-clamp recording of STOC in whole cell mode. We used a signal mass approach to measure the total Ca2+ released at a site and to estimate the Ca2+ current flowing through RyR [ ICa(spark)]. The variance between spark sites was significantly greater than the intrasite variance for the following parameters: Ca2+ signal mass, ICa(spark), STOC amplitude, and 5-ms isochronic STOC amplitude. Sites that failed to generate STOC did so consistently, while those at the remaining sites generated STOC without failure, allowing the sites to be divided into STOC-generating and STOC-less sites. We also determined the average number of spark sites, which was 42/cell at a minimum and more likely on the order of at least 400/cell. We conclude that 1) spark sites differ in the number of RyR, BK channels, and coupling ratio of RyR-BK channels, and 2) there are numerous Ca2+ spark-generating sites in smooth muscle cells. The implications of these findings for the organization of the spark microdomain are explored.
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Pérez, Guillermo J., Adrian D. Bonev, Joseph B. Patlak, and Mark T. Nelson. "Functional Coupling of Ryanodine Receptors to KCa Channels in Smooth Muscle Cells from Rat Cerebral Arteries." Journal of General Physiology 113, no. 2 (February 1, 1999): 229–38. http://dx.doi.org/10.1085/jgp.113.2.229.
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The relationship between Ca2+ release (“Ca2+ sparks”) through ryanodine-sensitive Ca2+ release channels in the sarcoplasmic reticulum and KCa channels was examined in smooth muscle cells from rat cerebral arteries. Whole cell potassium currents at physiological membrane potentials (−40 mV) and intracellular Ca2+ were measured simultaneously, using the perforated patch clamp technique and a laser two-dimensional (x–y) scanning confocal microscope and the fluorescent Ca2+ indicator, fluo-3. Virtually all (96%) detectable Ca2+ sparks were associated with the activation of a spontaneous transient outward current (STOC) through KCa channels. A small number of sparks (5 of 128) were associated with currents smaller than 6 pA (mean amplitude, 4.7 pA, at −40 mV). Approximately 41% of STOCs occurred without a detectable Ca2+ spark. The amplitudes of the Ca2+ sparks correlated with the amplitudes of the STOCs (regression coefficient 0.8; P < 0.05). The half time of decay of Ca2+ sparks (56 ms) was longer than the associated STOCs (9 ms). The mean amplitude of the STOCs, which were associated with Ca2+ sparks, was 33 pA at −40 mV. The mean amplitude of the “sparkless” STOCs was smaller, 16 pA. The very significant increase in KCa channel open probability (>104-fold) during a Ca2+ spark is consistent with local Ca2+ during a spark being in the order of 1–100 μM. Therefore, the increase in fractional fluorescence (F/Fo) measured during a Ca2+ spark (mean 2.04 F/Fo or ∼310 nM Ca2+) appears to significantly underestimate the local Ca2+ that activates KCa channels. These results indicate that the majority of ryanodine receptors that cause Ca2+ sparks are functionally coupled to KCa channels in the surface membrane, providing direct support for the idea that Ca2+ sparks cause STOCs.
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Chun, Lois G., Christopher W. Ward, and Martin F. Schneider. "Ca2+ sparks are initiated by Ca2+ entry in embryonic mouse skeletal muscle and decrease in frequency postnatally." American Journal of Physiology-Cell Physiology 285, no. 3 (September 2003): C686—C697. http://dx.doi.org/10.1152/ajpcell.00072.2003.
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“Spontaneous” Ca2+ sparks and ryanodine receptor type 3 (RyR3) expression are readily detected in embryonic mammalian skeletal muscle but not in adult mammalian muscle, which rarely exhibits Ca2+ sparks and expresses predominantly RyR1. We have used confocal fluorescence imaging and systematic sampling of enzymatically dissociated single striated muscle fibers containing the Ca2+ indicator dye fluo 4 to show that the frequency of spontaneous Ca2+ sparks decreases dramatically from embryonic day 18 (E18) to postnatal day 14 (P14) in mouse diaphragm and from P1 to P14 in mouse extensor digitorum longus fibers. In contrast, the relative levels of RyR3 to RyR1 protein remained constant in diaphragm muscles from E18 to P14, indicating that changes in relative levels of RyR isoform expression did not cause the decline in Ca2+ spark frequency. E18 diaphragm fibers were used to investigate possible mechanisms underlying spark initiation in embryonic fibers. Spark frequency increased or decreased, respectively, when E18 diaphragm fibers were exposed to 8 or 0 mM Ca2+ in the extracellular Ringer solution, with no change in either the average resting fiber fluo 4 fluorescence or the average properties of the sparks. Either CoCl2 (5 mM) or nifedipine (30 μM) markedly decreased spark frequency in E18 diaphragm fibers. These results indicate that Ca2+ sparks may be triggered by locally elevated [Ca2+] due to Ca2+ influx via dihydropyridine receptor L-type Ca2+ channels in embryonic mammalian skeletal muscle.
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González, A., W. G. Kirsch, N. Shirokova, G. Pizarro, M. D. Stern, and E. Ríos. "The Spark and Its Ember." Journal of General Physiology 115, no. 2 (February 1, 2000): 139–58. http://dx.doi.org/10.1085/jgp.115.2.139.
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Amplitude, spatial width, and rise time of Ca2+ sparks were compared in frog fast-twitch muscle, in three conditions that alter activation of release channels by [Ca2+]. A total of ∼17,000 sparks from 30 cells were evaluated. In cells under voltage clamp, caffeine (0.5 or 1 mM) increased average spark width by 28%, rise time by 18%, and amplitude by 7%. Increases in width were significant even among events of the same rise time. Spontaneous events recorded in permeabilized fibers with low internal [Mg2+] (0.4 mM), had width and rise times greater than in reference, and not significantly different than those in caffeine. The spark average in reference rides on a continuous fluorescence “ridge” and is continued by an “ember,” a prolongation of width ∼1 μm and amplitude <0.2, vanishing in ∼100 ms. Ridge and ember were absent in caffeine and in permeabilized cells. Exposure of voltage-clamped cells to high internal [Mg2+] (7 mM) had effects opposite to caffeine, reducing spark width by 26% and amplitude by 27%. In high [Mg2+], the ember was visible in individual sparks as a prolongation of variable duration and amplitude up to 1.2. Based on simulations and calculation of Ca2+ release flux from averaged sparks, the increase in spark width caused by caffeine was interpreted as evidence of an increase in radius of the release source—presumably by recruitment of additional channels. Conversely, spark narrowing suggests loss of contributing channels in high Mg2+. Therefore, these changes in spark width at constant rise times are evidence of a multichannel origin of sparks. Because ridge and ember were reduced by promoters of Ca2+-dependent activation (caffeine, low [Mg2+]) and became more visible in the presence of its inhibitors, they are probably manifestations of Ca2+ release directly operated by voltage sensors.
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Hollingworth, Stephen, W. Knox Chandler, and Stephen M. Baylor. "Effects of Tetracaine on Voltage-activated Calcium Sparks in Frog Intact Skeletal Muscle Fibers." Journal of General Physiology 127, no. 3 (February 27, 2006): 291–307. http://dx.doi.org/10.1085/jgp.200509477.
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The properties of Ca2+ sparks in frog intact skeletal muscle fibers depolarized with 13 mM [K+] Ringer's are well described by a computational model with a Ca2+ source flux of amplitude 2.5 pA (units of current) and duration 4.6 ms (18 °C; Model 2 of Baylor et al., 2002). This result, in combination with the values of single-channel Ca2+ current reported for ryanodine receptors (RyRs) in bilayers under physiological ion conditions, 0.5 pA (Kettlun et al., 2003) to 2 pA (Tinker et al., 1993), suggests that 1–5 RyR Ca2+ release channels open during a voltage-activated Ca2+ spark in an intact fiber. To distinguish between one and greater than one channel per spark, sparks were measured in 8 mM [K+] Ringer's in the absence and presence of tetracaine, an inhibitor of RyR channel openings in bilayers. The most prominent effect of 75–100 μM tetracaine was an approximately sixfold reduction in spark frequency. The remaining sparks showed significant reductions in the mean values of peak amplitude, decay time constant, full duration at half maximum (FDHM), full width at half maximum (FWHM), and mass, but not in the mean value of rise time. Spark properties in tetracaine were simulated with an updated spark model that differed in minor ways from our previous model. The simulations show that (a) the properties of sparks in tetracaine are those expected if tetracaine reduces the number of active RyR Ca2+ channels per spark, and (b) the single-channel Ca2+ current of an RyR channel is ≤1.2 pA under physiological conditions. The results support the conclusion that some normal voltage-activated sparks (i.e., in the absence of tetracaine) are produced by two or more active RyR Ca2+ channels. The question of how the activation of multiple RyRs is coordinated is discussed.
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Remillard, Carmelle V., Wei-Min Zhang, Larissa A. Shimoda, and James S. K. Sham. "Physiological properties and functions of Ca2+sparks in rat intrapulmonary arterial smooth muscle cells." American Journal of Physiology-Lung Cellular and Molecular Physiology 283, no. 2 (August 1, 2002): L433—L444. http://dx.doi.org/10.1152/ajplung.00468.2001.
Full textAbstract:
Ca+spark has been implicated as a pivotal feedback mechanism for regulating membrane potential and vasomotor tone in systemic arterial smooth muscle cells (SASMCs), but little is known about its properties in pulmonary arterial smooth muscle cells (PASMCs). Using confocal microscopy, we identified spontaneous Ca2+ sparks in rat intralobar PASMCs and characterized their spatiotemporal properties and physiological functions. Ca2+ sparks of PASMCs had a lower frequency and smaller amplitude than cardiac sparks. They were abolished by inhibition of ryanodine receptors but not by inhibition of inositol trisphosphate receptors and L-type Ca2+ channels. Enhanced Ca2+ influx by BAY K8644, K+, or high Ca2+ caused a significant increase in spark frequency. Functionally, enhancing Ca2+ sparks with caffeine (0.5 mM) caused membrane depolarization in PASMCs, in contrast to hyperpolarization in SASMCs. Norepinephrine and endothelin-1 both caused global elevations in cytosolic Ca2+ concentration ([Ca2+]), but only endothelin-1 increased spark frequency. These results suggest that Ca2+ sparks of PASMCs are similar to those of SASMCs, originate from ryanodine receptors, and are enhanced by Ca2+ influx. However, they play a different modulatory role on membrane potential and are under agonist-specific regulation independent of global [Ca2+].
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Li, Anlong, Adebowale Adebiyi, Charles W. Leffler, and Jonathan H. Jaggar. "KCa channel insensitivity to Ca2+ sparks underlies fractional uncoupling in newborn cerebral artery smooth muscle cells." American Journal of Physiology-Heart and Circulatory Physiology 291, no. 3 (September 2006): H1118—H1125. http://dx.doi.org/10.1152/ajpheart.01308.2005.
Full textAbstract:
In smooth muscle cells, localized intracellular Ca2+ transients, termed “Ca2+ sparks,” activate several large-conductance Ca2+-activated K+ (KCa) channels, resulting in a transient KCa current. In some smooth muscle cell types, a significant proportion of Ca2+ sparks do not activate KCa channels. The goal of this study was to explore mechanisms that underlie fractional Ca2+ spark-KCa channel coupling. We investigated whether membrane depolarization or ryanodine-sensitive Ca2+ release (RyR) channel activation modulates coupling in newborn (1- to 3-day-old) porcine cerebral artery myocytes. At steady membrane potentials of −40, 0, and +40 mV, mean transient KCa current frequency was ∼0.18, 0.43, and 0.26 Hz and KCa channel activity [number of KCa channels activated by Ca2+ sparks × open probability of KCa channels at peak of Ca2+ sparks ( NPo)] at the transient KCa current peak was ∼4, 12, and 24, respectively. Depolarization between −40 and +40 mV increased KCa channel sensitivity to Ca2+ sparks and elevated the percentage of Ca2+ sparks that activated a transient KCa current from 59 to 86%. In a Ca2+-free bath solution or in diltiazem, a voltage-dependent Ca2+ channel blocker, steady membrane depolarization between −40 and +40 mV increased transient KCa current frequency up to ∼1.6-fold. In contrast, caffeine (10 μM), an RyR channel activator, increased mean transient KCa current frequency but did not alter Ca2+ spark-KCa channel coupling. These data indicate that coupling is increased by mechanisms that elevate KCa channel sensitivity to Ca2+ sparks, but not by RyR channel activation. Overall, KCa channel insensitivity to Ca2+ sparks is a prominent factor underlying fractional Ca2+ spark uncoupling in newborn cerebral artery myocytes.
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Shkryl, Vyacheslav M., Lothar A. Blatter, and Eduardo Ríos. "Properties of Ca2+ sparks revealed by four-dimensional confocal imaging of cardiac muscle." Journal of General Physiology 139, no. 3 (February 13, 2012): 189–207. http://dx.doi.org/10.1085/jgp.201110709.
Full textAbstract:
Parameters (amplitude, width, kinetics) of Ca2+ sparks imaged confocally are affected by errors when the spark source is not in focus. To identify sparks that were in focus, we used fast scanning (LSM 5 LIVE; Carl Zeiss) combined with fast piezoelectric focusing to acquire x–y images in three planes at 1-µm separation (x-y-z-t mode). In 3,000 x–y scans in each of 34 membrane-permeabilized cat atrial cardiomyocytes, 6,906 sparks were detected. 767 sparks were in focus. They had greater amplitude, but their spatial width and rise time were similar compared with all sparks recorded. Their distribution of amplitudes had a mode at ΔF/F0 = 0.7. The Ca2+ release current underlying in-focus sparks was 11 pA, requiring 20 to 30 open channels, a number at the high end of earlier estimates. Spark frequency was greater than in earlier imaging studies of permeabilized ventricular cells, suggesting a greater susceptibility to excitation, which could have functional relevance for atrial cells. Ca2+ release flux peaked earlier than the time of peak fluorescence and then decayed, consistent with significant sarcoplasmic reticulum (SR) depletion. The evolution of fluorescence and release flux were strikingly similar for in-focus sparks of different rise time (T). Spark termination involves both depletion of Ca2+ in the SR and channel closure, which may be synchronized by depletion. The observation of similar flux in sparks of different T requires either that channel closure and other termination processes be independent of the determinants of flux (including [Ca2+]SR) or that different channel clusters respond to [Ca2+]SR with different sensitivity.
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Jaggar, Jonathan H., Andrá S. Stevenson, and Mark T. Nelson. "Voltage dependence of Ca2+sparks in intact cerebral arteries." American Journal of Physiology-Cell Physiology 274, no. 6 (June 1, 1998): C1755—C1761. http://dx.doi.org/10.1152/ajpcell.1998.274.6.c1755.
Full textAbstract:
Ca2+ sparks have been previously described in isolated smooth muscle cells. Here we present the first measurements of local Ca2+ transients (“Ca2+ sparks”) in an intact smooth muscle preparation. Ca2+sparks appear to result from the opening of ryanodine-sensitive Ca2+ release (RyR) channels in the sarcoplasmic reticulum (SR). Intracellular Ca2+ concentration ([Ca2+]i) was measured in intact cerebral arteries (40–150 μm in diameter) from rats, using the fluorescent Ca2+ indicator fluo 3 and a laser scanning confocal microscope. Membrane potential depolarization by elevation of external K+ from 6 to 30 mM increased Ca2+ spark frequency (4.3-fold) and amplitude (∼2-fold) as well as global arterial wall [Ca2+]i(∼1.7-fold). The half time of decay (∼50 ms) was not affected by membrane potential depolarization. Ryanodine (10 μM), which inhibits RyR channels and Ca2+ sparks in isolated cells, and thapsigargin (100 nM), which indirectly inhibits RyR channels by blocking the SR Ca2+-ATPase, completely inhibited Ca2+ sparks in intact cerebral arteries. Diltiazem, an inhibitor of voltage-dependent Ca2+ channels, lowered global [Ca2+]iand Ca2+ spark frequency and amplitude in intact cerebral arteries in a concentration-dependent manner. The frequency of Ca2+sparks (<1 s−1 ⋅ cell−1), even under conditions of steady depolarization, was too low to contribute significant amounts of Ca2+ to global Ca2+ in intact arteries. These results provide direct evidence that Ca2+ sparks exist in quiescent smooth muscle cells in intact arteries and that changes of membrane potential that would simulate physiological changes modulate both Ca2+ spark frequency and amplitude in arterial smooth muscle.
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Jaggar, Jonathan H., Valerie A. Porter, W. Jonathan Lederer, and Mark T. Nelson. "Calcium sparks in smooth muscle." American Journal of Physiology-Cell Physiology 278, no. 2 (February 1, 2000): C235—C256. http://dx.doi.org/10.1152/ajpcell.2000.278.2.c235.
Full textAbstract:
Local intracellular Ca2+transients, termed Ca2+ sparks, are caused by the coordinated opening of a cluster of ryanodine-sensitive Ca2+ release channels in the sarcoplasmic reticulum of smooth muscle cells. Ca2+ sparks are activated by Ca2+ entry through dihydropyridine-sensitive voltage-dependent Ca2+ channels, although the precise mechanisms of communication of Ca2+ entry to Ca2+ spark activation are not clear in smooth muscle. Ca2+ sparks act as a positive-feedback element to increase smooth muscle contractility, directly by contributing to the global cytoplasmic Ca2+ concentration ([Ca2+]) and indirectly by increasing Ca2+ entry through membrane potential depolarization, caused by activation of Ca2+ spark-activated Cl− channels. Ca2+ sparks also have a profound negative-feedback effect on contractility by decreasing Ca2+ entry through membrane potential hyperpolarization, caused by activation of large-conductance, Ca2+-sensitive K+ channels. In this review, the roles of Ca2+sparks in positive- and negative-feedback regulation of smooth muscle function are explored. We also propose that frequency and amplitude modulation of Ca2+ sparks by contractile and relaxant agents is an important mechanism to regulate smooth muscle function.
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Cheng, Xiaoyang, and Jonathan H. Jaggar. "Genetic ablation of caveolin-1 modifies Ca2+ spark coupling in murine arterial smooth muscle cells." American Journal of Physiology-Heart and Circulatory Physiology 290, no. 6 (June 2006): H2309—H2319. http://dx.doi.org/10.1152/ajpheart.01226.2005.
Full textAbstract:
L-type, voltage-dependent calcium (Ca2+) channels, ryanodine-sensitive Ca2+ release (RyR) channels, and large-conductance Ca2+-activated potassium (KCa) channels comprise a functional unit that regulates smooth muscle contractility. Here, we investigated whether genetic ablation of caveolin-1 (cav-1), a caveolae protein, alters Ca2+ spark to KCa channel coupling and Ca2+ spark regulation by voltage-dependent Ca2+ channels in murine cerebral artery smooth muscle cells. Caveolae were abundant in the sarcolemma of control (cav-1+/+) cells but were not observed in cav-1-deficient (cav-1−/−) cells. Ca2+ spark and transient KCa current frequency were approximately twofold higher in cav-1−/− than in cav-1+/+ cells. Although voltage-dependent Ca2+ current density was similar in cav-1+/+ and cav-1−/− cells, diltiazem and Cd2+, voltage-dependent Ca2+ channel blockers, reduced transient KCa current frequency to ∼55% of control in cav-1+/+ cells but did not alter transient KCa current frequency in cav-1−/− cells. Furthermore, although KCa channel density was elevated in cav-1−/− cells, transient KCa current amplitude was similar to that in cav-1+/+ cells. Higher Ca2+ spark frequency in cav-1−/− cells was not due to elevated intracellular Ca2+ concentration, sarcoplasmic reticulum Ca2+ load, or nitric oxide synthase activity. Similarly, Ca2+ spark amplitude and spread, the percentage of Ca2+ sparks that activated a transient KCa current, the amplitude relationship between sparks and transient KCa currents, and KCa channel conductance and apparent Ca2+ sensitivity were similar in cav-1+/+ and cav-1−/− cells. In summary, cav-1 ablation elevates Ca2+ spark and transient KCa current frequency, attenuates the coupling relationship between voltage-dependent Ca2+ channels and RyR channels that generate Ca2+ sparks, and elevates KCa channel density but does not alter transient KCa current activation by Ca2+ sparks. These findings indicate that cav-1 is required for physiological Ca2+ spark and transient KCa current regulation in cerebral artery smooth muscle cells.
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Yip, Kay-Pong, Lavanya Balasubramanian, Chen Kan, Lei Wang, Ruisheng Liu, Luisa Ribeiro-Silva, and James S. K. Sham. "Intraluminal pressure triggers myogenic response via activation of calcium spark and calcium-activated chloride channel in rat renal afferent arteriole." American Journal of Physiology-Renal Physiology 315, no. 6 (December 1, 2018): F1592—F1600. http://dx.doi.org/10.1152/ajprenal.00239.2018.
Full textAbstract:
Myogenic contraction of renal arterioles is an important regulatory mechanism for renal blood flow autoregulation. We have previously demonstrated that integrin-mediated mechanical force increases the occurrence of Ca2+ sparks in freshly isolated renal vascular smooth muscle cells (VSMCs). To further test whether the generation of Ca2+ sparks is a downstream signal of mechanotransduction in pressure-induced myogenic constriction, the relationship between Ca2+ sparks and transmural perfusion pressure was investigated in intact VSMCs of pressurized rat afferent arterioles. Spontaneous Ca2+ sparks were found in VSMCs when afferent arterioles were perfused at 80 mmHg. The spark frequency was significantly increased when perfusion pressure was increased to 120 mmHg. A similar increase of spark frequency was also observed in arterioles stimulated with β1-integrin-activating antibody. Moreover, spark frequency was significantly higher in arterioles of spontaneous hypertensive rats at 80 and 120 mmHg. Spontaneous membrane current recorded using whole cell perforated patch in renal VSMCs showed predominant activity of spontaneous transient inward currents instead of spontaneous transient outward currents when holding potential was set close to physiological resting membrane potential. Real-time PCR and immunohistochemistry confirmed the expression of Ca2+-activated Cl− channel (ClCa) TMEM16A in renal VSMCs. Inhibition of TMEM16A with T16Ainh-A01 impaired the pressure-induced myogenic contraction in perfused afferent arterioles. Our study, for the first time to our knowledge, detected Ca2+ sparks in VSMCs of intact afferent arterioles, and their frequencies were positively modulated by the perfusion pressure. Our results suggest that Ca2+ sparks may couple to ClCa channels and trigger pressure-induced myogenic constriction via membrane depolarization.
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ZhuGe, Ronghua, Kevin E. Fogarty, Richard A. Tuft, Lawrence M. Lifshitz, Kemal Sayar, and John V. Walsh. "Dynamics of Signaling between Ca2+ Sparks and Ca2+- Activated K+ Channels Studied with a Novel Image-Based Method for Direct Intracellular Measurement of Ryanodine Receptor Ca2+ Current." Journal of General Physiology 116, no. 6 (December 1, 2000): 845–64. http://dx.doi.org/10.1085/jgp.116.6.845.
Full textAbstract:
Ca2+ sparks are highly localized cytosolic Ca2+ transients caused by a release of Ca2+ from the sarcoplasmic reticulum via ryanodine receptors (RyRs); they are the elementary events underlying global changes in Ca2+ in skeletal and cardiac muscle. In smooth muscle and some neurons, Ca2+ sparks activate large conductance Ca2+-activated K+ channels (BK channels) in the spark microdomain, causing spontaneous transient outward currents (STOCs) that regulate membrane potential and, hence, voltage-gated channels. Using the fluorescent Ca2+ indicator fluo-3 and a high speed widefield digital imaging system, it was possible to capture the total increase in fluorescence (i.e., the signal mass) during a spark in smooth muscle cells, which is the first time such a direct approach has been used in any system. The signal mass is proportional to the total quantity of Ca2+ released into the cytosol, and its rate of rise is proportional to the Ca2+ current flowing through the RyRs during a spark (ICa(spark)). Thus, Ca2+ currents through RyRs can be monitored inside the cell under physiological conditions. Since the magnitude of ICa(spark) in different sparks varies more than fivefold, Ca2+ sparks appear to be caused by the concerted opening of a number of RyRs. Sparks with the same underlying Ca2+ current cause STOCs, whose amplitudes vary more than threefold, a finding that is best explained by variability in coupling ratio (i.e., the ratio of RyRs to BK channels in the spark microdomain). The time course of STOC decay is approximated by a single exponential that is independent of the magnitude of signal mass and has a time constant close to the value of the mean open time of the BK channels, suggesting that STOC decay reflects BK channel kinetics, rather than the time course of [Ca2+] decline at the membrane. Computer simulations were carried out to determine the spatiotemporal distribution of the Ca2+ concentration resulting from the measured range of ICa(spark). At the onset of a spark, the Ca2+ concentration within 200 nm of the release site reaches a plateau or exceeds the [Ca2+]EC50 for the BK channels rapidly in comparison to the rate of rise of STOCs. These findings suggest a model in which the BK channels lie close to the release site and are exposed to a saturating [Ca2+] with the rise and fall of the STOCs determined by BK channel kinetics. The mechanism of signaling between RyRs and BK channels may provide a model for Ca2+ action on a variety of molecular targets within cellular microdomains.
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Pérez, Guillermo J., Adrian D. Bonev, and Mark T. Nelson. "Micromolar Ca2+ from sparks activates Ca2+-sensitive K+ channels in rat cerebral artery smooth muscle." American Journal of Physiology-Cell Physiology 281, no. 6 (December 1, 2001): C1769—C1775. http://dx.doi.org/10.1152/ajpcell.2001.281.6.c1769.
Full textAbstract:
The goal of the present study was to test the hypothesis that local Ca2+ release events (Ca2+ sparks) deliver high local Ca2+concentration to activate nearby Ca2+-sensitive K+ (BK) channels in the cell membrane of arterial smooth muscle cells. Ca2+ sparks and BK channels were examined in isolated myocytes from rat cerebral arteries with laser scanning confocal microscopy and patch-clamp techniques. BK channels had an apparent dissociation constant for Ca2+ of 19 μM and a Hill coefficient of 2.9 at −40 mV. At near-physiological intracellular Ca2+ concentration ([Ca2+]i; 100 nM) and membrane potential (−40 mV), the open probability of a single BK channel was low (1.2 × 10−6). A Ca2+spark increased BK channel activity to 18. Assuming that 1–100% of the BK channels are activated by a single Ca2+ spark, BK channel activity increases 6 × 105-fold to 6 × 103-fold, which corresponds to ∼30 μM to 4 μM spark Ca2+ concentration. 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid acetoxymethyl ester caused the disappearance of all Ca2+sparks while leaving the transient BK currents unchanged. Our results support the idea that Ca2+ spark sites are in close proximity to the BK channels and that local [Ca2+]i reaches micromolar levels to activate BK channels.
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Zhou, Jingsong, Bradley S. Launikonis, Eduardo Ríos, and Gustavo Brum. "Regulation of Ca2+ Sparks by Ca2+ and Mg2+ in Mammalian and Amphibian Muscle. An RyR Isoform-specific Role in Excitation–Contraction Coupling?" Journal of General Physiology 124, no. 4 (September 27, 2004): 409–28. http://dx.doi.org/10.1085/jgp.200409105.
Full textAbstract:
Ca2+ and Mg2+ are important mediators and regulators of intracellular Ca2+ signaling in muscle. The effects of changes of cytosolic [Ca2+] or [Mg2+] on elementary Ca2+ release events were determined, as functions of concentration and time, in single fast-twitch permeabilized fibers of rat and frog. Ca2+ sparks were identified and their parameters measured in confocal images of fluo-4 fluorescence. Solutions with different [Ca2+] or [Mg2+] were rapidly exchanged while imaging. Faster and spatially homogeneous changes of [Ca2+] (reaching peaks >100 μM) were achieved by photolysing Ca NP-EGTA with laser flashes. In both species, incrementing cytosolic [Ca2+] caused a steady, nearly proportional increase in spark frequency, reversible upon [Ca2+] reduction. A greater change in spark frequency, usually transient, followed sudden increases in [Ca2+] after a lag of 100 ms or more. The nonlinearity, lag, and other features of this delayed effect suggest that it requires increase of [Ca2+] inside the SR. In the frog only, increases in cytosolic [Ca2+] often resulted, after a lag, in sparks that propagated transversally. An increase in [Mg2+] caused a fall of spark frequency, but with striking species differences. In the rat, but not the frog, sparks were observed at 4–40 mM [Mg2+]. Reducing [Mg2+] below 2 mM, which should enable the RyR channel's activation (CICR) site to bind Ca2+, caused progressive increase in spark frequency in the frog, but had no effect in the rat. Spark propagation and enhancement by sub-mM Mg2+ are hallmarks of CICR. Their absence in the rat suggests that CICR requires RyR3 para-junctional clusters, present only in the frog. The observed frequency of sparks corresponds to a channel open probability of 10−7 in the frog or 10−8 in the rat. Together with the failure of photorelease to induce activation directly, this indicates a basal inhibition of channels in situ. It is proposed that relief of this inhibition could be the mechanism by which increased SR load increases spark frequency.
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Williams, Beatrice A., and Stephen M. Sims. "Calcium sparks activate calcium-dependent Cl− current in rat corpus cavernosum smooth muscle cells." American Journal of Physiology-Cell Physiology 293, no. 4 (October 2007): C1239—C1251. http://dx.doi.org/10.1152/ajpcell.00553.2006.
Full textAbstract:
Spontaneous transient currents, due to activation of Ca2+-dependent K+ and Cl− channels, occur in corpus cavernosum smooth muscle cells (CCSMC) of the penis. The Ca2+ events responsible for triggering Ca2+-dependent Cl− channels have never been identified in vascular muscle. We used high-speed fluorescence imaging combined with patch-clamp electrophysiology to provide the first characterization of Ca2+ events underlying these currents. Freshly isolated rat CCSMC loaded with fluo-4 exhibited localized, spontaneous elevations of intracellular Ca2+ (Ca2+ sparks) in 57% of cells. There was an average of 6.4 ± 0.5 release sites/cell with a frequency of 0.9 ± 1 Hz/cell and peak amplitude ΔF/Fo of 67 ± 10%. We addressed the controversy of whether these events are mediated by ryanodine or inositol 1,4,5 trisphosphate (IP3) receptors. Caffeine caused either a global Ca2+ rise at high concentrations or an increase in spark frequency at lower concentrations, whereas ryanodine dramatically reduced the amplitude and frequency of sparks. 2-Aminoethoxydiphenyl borate, an inhibitor of IP3 receptors, had no effect on spark frequency. Combined imaging and electrophysiological recording revealed strong coupling between Ca2+ sparks and biphasic transient currents, a relationship never before shown in vascular muscle. Moreover, spark frequency increased on depolarization, an effect abolished with the blockade of Ca2+ channels, consistent with Ca2+ influx regulating Ca2+ release from stores. We establish for the first time that Ca2+ sparks occur in CCSMC and arise from Ca2+ release through ryanodine receptors. Moreover, the voltage dependence of spark frequency demonstrated here provides novel functional evidence for voltage-dependent Ca2+ influx in CCSMC.
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Rodney, George G. "Calmodulin in adult mammalian skeletal muscle: localization and effect on sarcoplasmic reticulum Ca2+ release." American Journal of Physiology-Cell Physiology 294, no. 5 (May 2008): C1288—C1297. http://dx.doi.org/10.1152/ajpcell.00033.2008.
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Calmodulin is a ubiquitous Ca2+ binding protein that binds to ryanodine rectors (RyR) and is thought to modulate its activity. Here we evaluated the effects of recombinant calmodulin on the rate of occurrence and spatial properties of Ca2+ sparks as an assay of activation in saponin-permeabilized mouse myofibers. Control myofibers exhibited a time-dependent increase and subsequent decrease in spark frequency. Recombinant wild-type calmodulin prevented the time-dependent appearance of Ca2+ sparks and decreased the derived Ca2+ flux from the sarcoplasmic reticulum during a spark by ∼37%. A recombinant Ca2+-insensitive form of calmodulin resulted in an instantaneous increase in spark frequency as well as an increase in the derived Ca2+ flux by ∼24%. Endogenous calmodulin was found to primarily localize to the Z-line. Surprisingly, removal of endogenous calmodulin did not alter the time dependence of Ca2+ spark appearance. These results indicate that calmodulin may not be essential for RyR1-dependent Ca2+ release in adult mammalian skeletal muscle.
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Jackson-Weaver, Olan, Jessica M. Osmond, Jay S. Naik, Laura V. Gonzalez Bosc, Benjimen R. Walker, and Nancy L. Kanagy. "Intermittent hypoxia in rats reduces activation of Ca2+ sparks in mesenteric arteries." American Journal of Physiology-Heart and Circulatory Physiology 309, no. 11 (December 1, 2015): H1915—H1922. http://dx.doi.org/10.1152/ajpheart.00179.2015.
Full textAbstract:
Ca+ sparks are vascular smooth muscle cell (VSMC) Ca2+-release events that are mediated by ryanodine receptors (RyR) and promote vasodilation by activating large-conductance Ca2+-activated potassium channels and inhibiting myogenic tone. We have previously reported that exposing rats to intermittent hypoxia (IH) to simulate sleep apnea augments myogenic tone in mesenteric arteries through loss of hydrogen sulfide (H2S)-induced dilation. Because we also observed that H2S can increase Ca2+ spark activity, we hypothesized that loss of H2S after IH exposure reduces Ca2+ spark activity and that blocking Ca2+ spark generation reduces H2S-induced dilation. Ca2+ spark activity was lower in VSMC of arteries from IH compared with sham-exposed rats. Furthermore, depolarizing VSMC by increasing luminal pressure (from 20 to 100 mmHg) or by elevating extracellular [K+] increased spark activity in VSMC of arteries from sham rats but had no effect in arteries from IH rats. Inhibiting endogenous H2S production in sham arteries prevented these increases. NaHS or phosphodiesterase inhibition increased spark activity to the same extent in sham and IH arteries. Depolarization-induced increases in Ca2+ spark activity were due to increased sparks per site, whereas H2S increases in spark activity were due to increased spark sites per cell. Finally, inhibiting Ca2+ spark activity with ryanodine (10 μM) enhanced myogenic tone in arteries from sham but not IH rats and blocked dilation to exogenous H2S in arteries from both sham and IH rats. Our results suggest that H2S regulates RyR activation and that H2S-induced dilation requires Ca2+ spark activation. IH exposure decreases endogenous H2S-dependent Ca2+ spark activation to cause membrane depolarization and enhance myogenic tone in mesenteric arteries.
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ZhuGe, Ronghua, Kevin E. Fogarty, Richard A. Tuft, and John V. Walsh. "Spontaneous Transient Outward Currents Arise from Microdomains Where BK Channels Are Exposed to a Mean Ca2+ Concentration on the Order of 10 μM during a Ca2+ Spark." Journal of General Physiology 120, no. 1 (June 10, 2002): 15–27. http://dx.doi.org/10.1085/jgp.20028571.
Full textAbstract:
Ca2+ sparks are small, localized cytosolic Ca2+ transients due to Ca2+ release from sarcoplasmic reticulum through ryanodine receptors. In smooth muscle, Ca2+ sparks activate large conductance Ca2+-activated K+ channels (BK channels) in the spark microdomain, thus generating spontaneous transient outward currents (STOCs). The purpose of the present study is to determine experimentally the level of Ca2+ to which the BK channels are exposed during a spark. Using tight seal, whole-cell recording, we have analyzed the voltage-dependence of the STOC conductance (g(STOC)), and compared it to the voltage-dependence of BK channel activation in excised patches in the presence of different [Ca2+]s. The Ca2+ sparks did not change in amplitude over the range of potentials of interest. In contrast, the magnitude of g(STOC) remained roughly constant from 20 to −40 mV and then declined steeply at more negative potentials. From this and the voltage dependence of BK channel activation, we conclude that the BK channels underlying STOCs are exposed to a mean [Ca2+] on the order of 10 μM during a Ca2+ spark. The membrane area over which a concentration ≥10 μM is reached has an estimated radius of 150–300 nm, corresponding to an area which is a fraction of one square micron. Moreover, given the constraints imposed by the estimated channel density and the Ca2+ current during a spark, the BK channels do not appear to be uniformly distributed over the membrane but instead are found at higher density at the spark site.
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Kamishima, T., and J. M. Quayle. "Ca2+-induced Ca2+ release in cardiac and smooth muscle cells." Biochemical Society Transactions 31, no. 5 (October 1, 2003): 943–46. http://dx.doi.org/10.1042/bst0310943.
Full textAbstract:
Ca2+ influx across plasma membranes may trigger Ca2+ release by activating ryanodine-sensitive receptors in the sarcoplasmic reticulum. This process is called Ca2+-induced Ca2+ release, and may be important in regulating cytosolic Ca2+ concentration ([Ca2+]i). In cardiac cells, the initial [Ca2+]i increase, caused by L-type Ca2+ current, is profoundly amplified with Ca2+ release. The synchronized opening of several ryanodine-sensitive Ca2+-releasing channels was detected as discreet and highly localized Ca2+ elevation, and termed as a ‘Ca2+ spark’. A Ca2+ spark is under local control of an L-type Ca2+ channel, and therefore a Ca2+ spark does not normally trigger subsequent Ca2+ sparks in the neighbouring area. In smooth muscle cells, the importance of Ca2+-induced Ca2+ release in elevating [Ca2+]i appears to differ among preparations and species. Significant elevation in [Ca2+]i during depolarization was attributed to Ca2+ release in some smooth muscle cells, but not in others. Ca2+ sparks are also identified in smooth muscle cells, and may play a role as functional elementary events for Ca2+-induced Ca2+ release. At rest, Ca2+ sparks may be also important in regulating smooth muscle membrane potential. Ca2+ sparks occurring at rest do not raise global [Ca2+]i, but trigger spontaneous transient outward currents (STOCs) or spontaneous transient inward currents (STICs), the former producing hyperpolarization; the latter, depolarization. Thus there may be multiple facets for Ca2+-induced Ca2+ release in regulating the contractile status of smooth muscle cells.
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Wang, Yan Feng. "The Exploration on Forming Processing Method by Multiple Sparks EDM." Advanced Materials Research 875-877 (February 2014): 1260–64. http://dx.doi.org/10.4028/www.scientific.net/amr.875-877.1260.
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Koide, Masayo, Matthew A. Nystoriak, Gayathri Krishnamoorthy, Kevin P. O'Connor, Adrian D. Bonev, Mark T. Nelson, and George C. Wellman. "Reduced Ca2+ Spark Activity after Subarachnoid Hemorrhage Disables BK Channel Control of Cerebral Artery Tone." Journal of Cerebral Blood Flow & Metabolism 31, no. 1 (August 25, 2010): 3–16. http://dx.doi.org/10.1038/jcbfm.2010.143.
Full textAbstract:
Intracellular Ca2+ release events (‘Ca2+ sparks’) and transient activation of large-conductance Ca2+-activated potassium (BK) channels represent an important vasodilator pathway in the cerebral vasculature. Considering the frequent occurrence of cerebral artery constriction after subarachnoid hemorrhage (SAH), our objective was to determine whether Ca2+ spark and BK channel activity were reduced in cerebral artery myocytes from SAH model rabbits. Using laser scanning confocal microscopy, we observed ∼50% reduction in Ca2+ spark activity, reflecting a decrease in the number of functional Ca2+ spark discharge sites. Patch-clamp electrophysiology showed a similar reduction in Ca2+ spark-induced transient BK currents, without change in BK channel density or single-channel properties. Consistent with a reduction in active Ca2+ spark sites, quantitative real-time PCR and western blotting revealed decreased expression of ryanodine receptor type 2 (RyR-2) and increased expression of the RyR-2-stabilizing protein, FKBP12.6, in the cerebral arteries from SAH animals. Furthermore, inhibitors of Ca2+ sparks (ryanodine) or BK channels (paxilline) constricted arteries from control, but not from SAH animals. This study shows that SAH-induced decreased subcellular Ca2+ signaling events disable BK channel activity, leading to cerebral artery constriction. This phenomenon may contribute to decreased cerebral blood flow and poor outcome after aneurysmal SAH.
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Bankhead, Peter, C. Norman Scholfield, Tim M. Curtis, and J. Graham McGeown. "Detecting Ca2+ sparks on stationary and varying baselines." American Journal of Physiology-Cell Physiology 301, no. 3 (September 2011): C717—C728. http://dx.doi.org/10.1152/ajpcell.00032.2011.
Full textAbstract:
Studies concerning the physiological significance of Ca2+ sparks often depend on the detection and measurement of large populations of events in noisy microscopy images. Automated detection methods have been developed to quickly and objectively distinguish potential sparks from noise artifacts. However, previously described algorithms are not suited to the reliable detection of sparks in images where the local baseline fluorescence and noise properties can vary significantly, and risk introducing additional bias when applied to such data sets. Here, we describe a new, conceptually straightforward approach to spark detection in linescans that addresses this issue by combining variance stabilization with local baseline subtraction. We also show that in addition to greatly increasing the range of images in which sparks can be automatically detected, the use of a more accurate noise model enables our algorithm to achieve similar detection sensitivities with fewer false positives than previous approaches when applied both to synthetic and experimental data sets. We propose, therefore, that it might be a useful tool for improving the reliability and objectivity of spark analysis in general, and describe how it might be further optimized for specific applications.
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Zhang, Wei-Min, Kay-Pong Yip, Mo-Jun Lin, Larissa A. Shimoda, Wen-Hong Li, and James S. K. Sham. "ET-1 activates Ca2+ sparks in PASMC: local Ca2+ signaling between inositol trisphosphate and ryanodine receptors." American Journal of Physiology-Lung Cellular and Molecular Physiology 285, no. 3 (September 2003): L680—L690. http://dx.doi.org/10.1152/ajplung.00067.2003.
Full textAbstract:
Ca+ sparks originating from ryanodine receptors (RyRs) are known to cause membrane hyperpolarization and vasorelaxation in systemic arterial myocytes. By contrast, we have found that Ca2+ sparks of pulmonary arterial smooth muscle cells (PASMCs) are associated with membrane depolarization and activated by endothelin-1 (ET-1), a potent vasoconstrictor that mediates/modulates acute and chronic hypoxic pulmonary vasoconstriction. In this study, we characterized the effects of ET-1 on the physical properties of Ca2+ sparks and probed the signal transduction mechanism for spark activation in rat intralobar PASMCs. Application of ET-1 at 0.1-10 nM caused concentration-dependent increases in frequency, duration, and amplitude of Ca2+ sparks. The ET-1-induced increase in spark frequency was inhibited by BQ-123, an ETA-receptor antagonist; by U-73122, a PLC inhibitor; and by xestospongin C and 2-aminoethyl diphenylborate, antagonists of inositol trisphosphate (IP3) receptors (IP3Rs). However, it was unrelated to sarcoplasmic reticulum Ca2+ content, activation of L-type Ca2+ channels, PKC, or cADP ribose. Photorelease of caged-IP3 indicated that Ca2+ release from IP3R could cross-activate RyRs to generate Ca2+ sparks. Immunocytochemistry showed that the distributions of IP3Rs and RyRs were similar in PASMCs. Moreover, inhibition of Ca2+ sparks with ryanodine caused a significant rightward shift in the ET-1 concentration-tension relationship in pulmonary arteries. These results suggest that ET-1 activation of Ca2+ sparks is mediated via the ETA receptor-PLC-IP3 pathway and local Ca2+ cross-signaling between IP3Rs and RyRs; in addition, this novel signaling mechanism contributes significantly to the ET-1-induced vasoconstriction in pulmonary arteries.
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Bonev, Adrian D., Jonathan H. Jaggar, Michael Rubart, and Mark T. Nelson. "Activators of protein kinase C decrease Ca2+ spark frequency in smooth muscle cells from cerebral arteries." American Journal of Physiology-Cell Physiology 273, no. 6 (December 1, 1997): C2090—C2095. http://dx.doi.org/10.1152/ajpcell.1997.273.6.c2090.
Full textAbstract:
Local Ca2+ transients (“Ca2+ sparks”) caused by the opening of one or the coordinated opening of a number of tightly clustered ryanodine-sensitive Ca2+-release (RyR) channels in the sarcoplasmic reticulum (SR) activate nearby Ca2+-dependent K+(KCa) channels to cause an outward current [referred to as a “spontaneous transient outward current” (STOC)]. These KCa currents cause membrane potential hyperpolarization of arterial myocytes, which would lead to vasodilation through decreasing Ca2+ entry through voltage-dependent Ca2+ channels. Therefore, modulation of Ca2+spark frequency should be a means to regulation of KCa channel currents and hence membrane potential. We examined the frequency modulation of Ca2+ sparks and STOCs by activation of protein kinase C (PKC). The PKC activators, phorbol 12-myristate 13-acetate (PMA; 10 nM) and 1,2-dioctanoyl- sn-glycerol (1 μM), decreased Ca2+ spark frequency by 72% and 60%, respectively, and PMA reduced STOC frequency by 83%. PMA also decreased STOC amplitude by 22%, which could be explained by an observed reduction (29%) in KCa channel open probability in the absence of Ca2+ sparks. The reduction in STOC frequency occurred in the presence of an inorganic blocker (Cd2+) of voltage-dependent Ca2+ channels. The reduction in Ca2+ spark frequency did not result from SR Ca2+ depletion, since caffeine-induced Ca2+ transients did not decrease in the presence of PMA. These results suggest that activators of PKC can modulate the frequency of Ca2+ sparks, through an effect on the RyR channel, which would decrease STOC frequency (i.e., KCa channel activity).
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Caruso, Angelo, and Carmela Strangio. "Statistical ignition of high density D-T fuel." Laser and Particle Beams 16, no. 1 (March 1998): 83–90. http://dx.doi.org/10.1017/s0263034600011794.
Full textAbstract:
In energy-oriented ICF, a nondeterministic ignition process can be acceptable, provided the ignition probability be large enough. We present fuel gain calculations for D-T assemblies ignited by a supercritical spark, statistically created within a cluster of many subcritical ones, at the end of an implosion process. It is assigned the total number of sparks and the probability of having at least one of them supercritical. Comparatively to the central, single-spark approach, the multi-spark scheme is characterized by relaxed symmetry requirements. This allows to consider as realistic the achievement of higher fuel densities and gains comparable (or higher) to those typical of the single-spark approach, as evaluated for currently accepted spark convergence ratios.
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Gusev, Konstantin, and Ernst Niggli. "Modulation of the Local SR Ca2+ Release by Intracellular Mg2+ in Cardiac Myocytes." Journal of General Physiology 132, no. 6 (November 24, 2008): 721–30. http://dx.doi.org/10.1085/jgp.200810119.
Full textAbstract:
In cardiac muscle, Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR) defines the amplitude and time course of the Ca2+ transient. The global elevation of the intracellular Ca2+ concentration arises from the spatial and temporal summation of elementary Ca2+ release events, Ca2+ sparks. Ca2+ sparks represent the concerted opening of a group of ryanodine receptors (RYRs), which are under the control of several modulatory proteins and diffusible cytoplasmic factors (e.g., Ca2+, Mg2+, and ATP). Here, we examined by which mechanism the free intracellular Mg2+ ([Mg2+]free) affects various Ca2+ spark parameters in permeabilized mouse ventricular myocytes, such as spark frequency, duration, rise time, and full width, at half magnitude and half maximal duration. Varying the levels of free ATP and Mg2+ in specifically designed solutions allowed us to separate the inhibition of RYRs by Mg2+ from the possible activation by ATP and Mg2+-ATP via the adenine binding site of the channel. Changes in [Mg2+]free generally led to biphasic alterations of the Ca2+ spark frequency. For example, lowering [Mg2+]free resulted in an abrupt increase of spark frequency, which slowly recovered toward the initial level, presumably as a result of SR Ca2+ depletion. Fitting the Ca2+ spark inhibition by [Mg2+]free with a Hill equation revealed a Ki of 0.1 mM. In conclusion, our results support the notion that local Ca2+ release and Ca2+ sparks are modulated by Mg2+ in the intracellular environment. This seems to occur predominantly by hindering Ca2+-dependent activation of the RYRs through competitive Mg2+ occupancy of the high-affinity activation site of the channels. These findings help to characterize CICR in cardiac muscle under normal and pathological conditions, where the levels of Mg2+ and ATP can change.
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Zhao, Guiling, Adebowale Adebiyi, Qi Xi, and Jonathan H. Jaggar. "Hypoxia reduces KCa channel activity by inducing Ca2+ spark uncoupling in cerebral artery smooth muscle cells." American Journal of Physiology-Cell Physiology 292, no. 6 (June 2007): C2122—C2128. http://dx.doi.org/10.1152/ajpcell.00629.2006.
Full textAbstract:
Arterial smooth muscle cell large-conductance Ca2+-activated potassium (KCa) channels have been implicated in modulating hypoxic dilation of systemic arteries, although this is controversial. KCa channel activity in arterial smooth muscle cells is controlled by localized intracellular Ca2+ transients, termed Ca2+ sparks, but hypoxic regulation of Ca2+ sparks and KCa channel activation by Ca2+ sparks has not been investigated. We report here that in voltage-clamped (−40 mV) cerebral artery smooth muscle cells, a reduction in dissolved O2 partial pressure from 150 to 15 mmHg reversibly decreased Ca2+ spark-induced transient KCa current frequency and amplitude to 61% and 76% of control, respectively. In contrast, hypoxia did not alter Ca2+ spark frequency, amplitude, global intracellular Ca2+ concentration, or sarcoplasmic reticulum Ca2+ load. Hypoxia reduced transient KCa current frequency by decreasing the percentage of Ca2+ sparks that activated a transient KCa current from 89% to 63%. Hypoxia reduced transient KCa current amplitude by attenuating the amplitude relationship between Ca2+ sparks that remained coupled and the evoked transient KCa currents. Consistent with these data, in inside-out patches at −40 mV hypoxia reduced KCa channel apparent Ca2+ sensitivity and increased the Kd for Ca2+ from ∼17 to 32 μM, but did not alter single-channel amplitude. In summary, data indicate that hypoxia reduces KCa channel apparent Ca2+ sensitivity via a mechanism that is independent of cytosolic signaling messengers, and this leads to uncoupling of KCa channels from Ca2+ sparks. Transient KCa current inhibition due to uncoupling would oppose hypoxic cerebrovascular dilation.
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Abdul Karim, Zainal Ambri, Muhammad Abdul Halim Mohammad Mursal, and Mohd Hanafiah Mat Jamlus. "High-Frequency Electromagnetic Waves for Diesel Soot Oxidation Strategy." Advanced Materials Research 875-877 (February 2014): 1382–86. http://dx.doi.org/10.4028/www.scientific.net/amr.875-877.1382.
Full textAbstract:
Results from an experimental investigation for diesel soot oxidation strategy using high-frequency electromagnetic waves in producing metal sparks is provided in this paper. It is envisaged that the micro plasma develop by metal when subjected to high-frequency electromagnetic waves, produces heat that enables soot oxidation process. The work attempts to investigate the relationship between spark inception of metals and micro plasma temperatures at different microwaves intensity. Various metal specimens were exposed to high-frequency electromagnetic waves at different power levels at a specific duration of time. The sparks temperatures or micro plasmas produced by the metals were measured using a high-range infrared thermometer. It was found that aluminum and brass have high spark temperatures when compared to mild steel at lower microwaves power levels. However, both aluminum and brass have lower melting point temperatures than mild steel. This makes the material unsuitable for prolong exposure to high-frequency electromagnetic waves. Mild steel was found the suitable metal to be used as the spark inceptor in the soot oxidation reaction chamber.
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ZhuGe, Ronghua, Richard A. Tuft, Kevin E. Fogarty, Karl Bellve, Fredric S. Fay, and John V. Walsh. "The Influence of Sarcoplasmic Reticulum Ca2+ Concentration on Ca2+ Sparks and Spontaneous Transient Outward Currents in Single Smooth Muscle Cells." Journal of General Physiology 113, no. 2 (February 1, 1999): 215–28. http://dx.doi.org/10.1085/jgp.113.2.215.
Full textAbstract:
Localized, transient elevations in cytosolic Ca2+, known as Ca2+ sparks, caused by Ca2+ release from sarcoplasmic reticulum, are thought to trigger the opening of large conductance Ca2+-activated potassium channels in the plasma membrane resulting in spontaneous transient outward currents (STOCs) in smooth muscle cells. But the precise relationships between Ca2+ concentration within the sarcoplasmic reticulum and a Ca2+ spark and that between a Ca2+ spark and a STOC are not well defined or fully understood. To address these problems, we have employed two approaches using single patch-clamped smooth muscle cells freshly dissociated from toad stomach: a high speed, wide-field imaging system to simultaneously record Ca2+ sparks and STOCs, and a method to simultaneously measure free global Ca2+ concentration in the sarcoplasmic reticulum ([Ca2+]SR) and in the cytosol ([Ca2+]CYTO) along with STOCs. At a holding potential of 0 mV, cells displayed Ca2+ sparks and STOCs. Ca2+ sparks were associated with STOCs; the onset of the sparks coincided with the upstroke of STOCs, and both had approximately the same decay time. The mean increase in [Ca2+]CYTO at the time and location of the spark peak was ∼100 nM above a resting concentration of ∼100 nM. The frequency and amplitude of spontaneous Ca2+ sparks recorded at −80 mV were unchanged for a period of 10 min after removal of extracellular Ca2+ (nominally Ca2+-free solution with 50 μM EGTA), indicating that Ca2+ influx is not necessary for Ca2+sparks. A brief pulse of caffeine (20 mM) elicited a rapid decrease in [Ca2+]SR in association with a surge in [Ca2+]CYTO and a fusion of STOCs, followed by a fast restoration of [Ca2+]CYTO and a gradual recovery of [Ca2+]SR and STOCs. The return of global [Ca2+]CYTO to rest was an order of magnitude faster than the refilling of the sarcoplasmic reticulum with Ca2+. After the global [Ca2+]CYTO was fully restored, recovery of STOC frequency and amplitude were correlated with the level of [Ca2+]SR, even though the time for refilling varied greatly. STOC frequency did not recover substantially until the [Ca2+]SR was restored to 60% or more of resting levels. At [Ca2+]SR levels above 80% of rest, there was a steep relationship between [Ca2+]SR and STOC frequency. In contrast, the relationship between [Ca2+]SR and STOC amplitude was linear. The relationship between [Ca2+]SR and the frequency and amplitude was the same for Ca2+ sparks as it was for STOCs. The results of this study suggest that the regulation of [Ca2+]SR might provide one mechanism whereby agents could govern Ca2+ sparks and STOCs. The relationship between Ca2+ sparks and STOCs also implies a close association between a sarcoplasmic reticulum Ca2+ release site and the Ca2+-activated potassium channels responsible for a STOC.
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Ritter, Michael, Zhi Su, Kenneth W. Spitzer, Hideyuki Ishida, and William H. Barry. "Caffeine-induced Ca2+ sparks in mouse ventricular myocytes." American Journal of Physiology-Heart and Circulatory Physiology 278, no. 2 (February 1, 2000): H666—H669. http://dx.doi.org/10.1152/ajpheart.2000.278.2.h666.
Full textAbstract:
Ca2+ sparks are spatially localized intracellular Ca2+ release events that were first described in 1993. Sparks have been ascribed to sarcoplasmic reticulum Ca2+ release channel (ryanodine receptor, RyR) opening induced by Ca2+ influx via L-type Ca2+ channels or by spontaneous RyR openings and have been thought to reflect Ca2+ release from a cluster of RyR. Here we describe a pharmacological approach to study sparks by exposing ventricular myocytes to caffeine with a rapid solution-switcher device. Sparks under these conditions have properties similar to naturally occurring sparks in terms of size and intracellular Ca2+ concentration ([Ca2+]i) amplitude. However, after the diffusion of caffeine, sparks first appear close to the cell surface membrane before coalescing to produce a whole cell transient. Our results support the idea that a whole cell [Ca2+]i transient consists of the summation of sparks and that Ca2+ sparks consist of the opening of a cluster of RyR and confirm that characteristics of the cluster rather than the L-type Ca2+ channel-RyR relation determine spark properties.
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Chandler, W. K., S. Hollingworth, and S. M. Baylor. "Simulation of Calcium Sparks in Cut Skeletal Muscle Fibers of the Frog." Journal of General Physiology 121, no. 4 (March 17, 2003): 311–24. http://dx.doi.org/10.1085/jgp.200308787.
Full textAbstract:
Spark mass, the volume integral of ΔF/F, was investigated theoretically and with simulations. These studies show that the amount of Ca2+ bound to fluo-3 is proportional to mass times the total concentration of fluo-3 ([fluo-3T]); the proportionality constant depends on resting Ca2+ concentration ([Ca2+]R). In the simulation of a Ca2+ spark in an intact frog fiber with [fluo-3T] = 100 μM, fluo-3 captures approximately one-fourth of the Ca2+ released from the sarcoplasmic reticulum (SR). Since mass in cut fibers is several times that in intact fibers, both with similar values of [fluo-3T] and [Ca2+]R, it seems likely that SR Ca2+ release is larger in cut fiber sparks or that fluo-3 is able to capture a larger fraction of the released Ca2+ in cut fibers, perhaps because of reduced intrinsic Ca2+ buffering. Computer simulations were used to identify these and other factors that may underlie the differences in mass and other properties of sparks in intact and cut fibers. Our spark model, which successfully simulates calcium sparks in intact fibers, was modified to reflect the conditions of cut fiber measurements. The results show that, if the protein Ca2+-buffering power of myoplasm is the same as that in intact fibers, the Ca2+ source flux underlying a spark in cut fibers is 5–10 times that in intact fibers. Smaller source fluxes are required for less buffer. In the extreme case in which Ca2+ binding to troponin is zero, the source flux needs to be 3–5 times that in intact fibers. An increased Ca2+ source flux could arise from an increase in Ca2+ flux through one ryanodine receptor (RYR) or an increase in the number of active RYRs per spark, or both. These results indicate that the gating of RYRs, or their apparent single channel Ca2+ flux, is different in frog cut fibers—and, perhaps, in other disrupted preparations—than in intact fibers.
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Jackson-Weaver, Olan, Jessica M. Osmond, Melissa A. Riddle, Jay S. Naik, Laura V. Gonzalez Bosc, Benjimen R. Walker, and Nancy L. Kanagy. "Hydrogen sulfide dilates rat mesenteric arteries by activating endothelial large-conductance Ca2+-activated K+ channels and smooth muscle Ca2+ sparks." American Journal of Physiology-Heart and Circulatory Physiology 304, no. 11 (June 1, 2013): H1446—H1454. http://dx.doi.org/10.1152/ajpheart.00506.2012.
Full textAbstract:
We have previously shown that hydrogen sulfide (H2S) reduces myogenic tone and causes relaxation of phenylephrine (PE)-constricted mesenteric arteries. This effect of H2S to cause vasodilation and vascular smooth muscle cell (VSMC) hyperpolarization was mediated by large-conductance Ca2+-activated potassium channels (BKCa). Ca2+ sparks are ryanodine receptor (RyR)-mediated Ca2+-release events that activate BKCa channels in VSMCs to cause membrane hyperpolarization and vasodilation. We hypothesized that H2S activates Ca2+ sparks in small mesenteric arteries. Ca2+ sparks were measured using confocal microscopy in rat mesenteric arteries loaded with the Ca2+ indicator fluo-4. VSMC membrane potential ( Em) was measured in isolated arteries using sharp microelectrodes. In PE-constricted arteries, the H2S donor NaHS caused vasodilation that was inhibited by ryanodine (RyR blocker), abluminal or luminal iberiotoxin (IbTx, BKCa blocker), endothelial cell (EC) disruption, and sulfaphenazole [cytochrome P-450 2C (Cyp2C) inhibitor]. The H2S donor NaHS (10 μmol/l) increased Ca2+ sparks but only in the presence of intact EC and this was blocked by sulfaphenazole or luminal IbTx. Inhibiting cystathionine γ-lyase (CSE)-derived H2S with β-cyano-l-alanine (BCA) also reduced VSMC Ca2+ spark frequency in mesenteric arteries, as did EC disruption. However, excess CSE substrate homocysteine did not affect spark activity. NaHS hyperpolarized VSMC Em in PE-depolarized mesenteric arteries with intact EC and also hyperpolarized EC E m in arteries cut open to expose the lumen. This hyperpolarization was prevented by ryanodine, sulfaphenazole, and abluminal or luminal IbTx. BCA reduced IbTx-sensitive K+ currents in freshly dispersed mesenteric ECs. These results suggest that H2S increases Ca2+ spark activity in mesenteric artery VSMC through activation of endothelial BKCa channels and Cyp2C, a novel vasodilatory pathway for this emerging signaling molecule.
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Ruiz-Hurtado, Gema, Linwei Li, María Fernández-Velasco, Angélica Rueda, Florence Lefebvre, Yueyi Wang, Philippe Mateo, et al. "Reconciling depressed Ca2+ sparks occurrence with enhanced RyR2 activity in failing mice cardiomyocytes." Journal of General Physiology 146, no. 4 (September 14, 2015): 295–306. http://dx.doi.org/10.1085/jgp.201511366.
Full textAbstract:
Abnormalities in cardiomyocyte Ca2+ handling contribute to impaired contractile function in heart failure (HF). Experiments on single ryanodine receptors (RyRs) incorporated into lipid bilayers have indicated that RyRs from failing hearts are more active than those from healthy hearts. Here, we analyzed spontaneous Ca2+ sparks (brief, localized increased in [Ca2+]i) to evaluate RyR cluster activity in situ in a mouse post-myocardial infarction (PMI) model of HF. The cardiac ejection fraction of PMI mice was reduced to ∼30% of that of sham-operated (sham) mice, and their cardiomyocytes were hypertrophied. The [Ca2+]i transient amplitude and sarcoplasmic reticulum (SR) Ca2+ load were decreased in intact PMI cardiomyocytes compared with those from sham mice, and spontaneous Ca2+ sparks were less frequent, whereas the fractional release and the frequency of Ca2+ waves were both increased, suggesting higher RyR activity. In permeabilized cardiomyocytes, in which the internal solution can be controlled, Ca2+ sparks were more frequent in PMI cells (under conditions of similar SR Ca2+ load), confirming the enhanced RyR activity. However, in intact cells from PMI mice, the Ca2+ sparks frequency normalized by the SR Ca2+ load in that cell were reduced compared with those in sham mice, indicating that the cytosolic environment in intact cells contributes to the decrease in Ca2+ spark frequency. Indeed, using an internal “failing solution” with less ATP (as found in HF), we observed a dramatic decrease in Ca2+ spark frequency in permeabilized PMI and sham myocytes. In conclusion, our data show that, even if isolated RyR channels show more activity in HF, concomitant alterations in intracellular media composition and SR Ca2+ load may mask these effects at the Ca2+ spark level in intact cells. Nonetheless, in this scenario, the probability of arrhythmogenic Ca2+ waves is enhanced, and they play a potential role in the increase in arrhythmia events in HF patients.
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Copello, Julio A., Aleksey V. Zima, Paula L. Diaz-Sylvester, Michael Fill, and Lothar A. Blatter. "Ca2+ entry-independent effects of L-type Ca2+ channel modulators on Ca2+ sparks in ventricular myocytes." American Journal of Physiology-Cell Physiology 292, no. 6 (June 2007): C2129—C2140. http://dx.doi.org/10.1152/ajpcell.00437.2006.
Full textAbstract:
During the cardiac action potential, Ca2+ entry through dyhidropyridine receptor L-type Ca2+ channels (DHPRs) activates ryanodine receptors (RyRs) Ca2+-release channels, resulting in massive Ca2+ mobilization from the sarcoplasmic reticulum (SR). This global Ca2+ release arises from spatiotemporal summation of many localized elementary Ca2+-release events, Ca2+ sparks. We tested whether DHPRs modulate Ca2+sparks in a Ca2+ entry-independent manner. Negative modulation by DHPR of RyRs via physical interactions is accepted in resting skeletal muscle but remains controversial in the heart. Ca2+ sparks were studied in cat cardiac myocytes permeabilized with saponin or internally perfused via a patch pipette. Bathing and pipette solutions contained low Ca2+ (100 nM). Under these conditions, Ca2+ sparks were detected with a stable frequency of 3–5 sparks·s−1·100 μm−1. The DHPR blockers nifedipine, nimodipine, FS-2, and calciseptine decreased spark frequency, whereas the DHPR agonists Bay-K8644 and FPL-64176 increased it. None of these agents altered the spatiotemporal characteristics of Ca2+ sparks. The DHPR modulators were also without effect on SR Ca2+ load (caffeine-induced Ca2+ transients) or sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity (Ca2+ loading rates of isolated SR microsomes) and did not change cardiac RyR channel gating (planar lipid bilayer experiments). In summary, DHPR modulators affected spark frequency in the absence of DHPR-mediated Ca2+ entry. This action could not be attributed to a direct action of DHPR modulators on SERCA or RyRs. Our results suggest that the activity of RyR Ca2+-release units in ventricular myocytes is modulated by Ca2+ entry-independent conformational changes in neighboring DHPRs.
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Michiels, Nico K., Victoria C. Seeburger, Nadine Kalb, Melissa G. Meadows, Nils Anthes, Amalia A. Mailli, and Colin B. Jack. "Controlled iris radiance in a diurnal fish looking at prey." Royal Society Open Science 5, no. 2 (February 2018): 170838. http://dx.doi.org/10.1098/rsos.170838.
Full textAbstract:
Active sensing using light, or active photolocation, is only known from deep sea and nocturnal fish with chemiluminescent ‘search’ lights. Bright irides in diurnal fish species have recently been proposed as a potential analogue. Here, we contribute to this discussion by testing whether iris radiance is actively modulated. The focus is on behaviourally controlled iris reflections, called ‘ocular sparks’. The triplefin Tripterygion delaisi can alternate between red and blue ocular sparks, allowing us to test the prediction that spark frequency and hue depend on background hue and prey presence. In a first experiment, we found that blue ocular sparks were significantly more often ‘on’ against red backgrounds, and red ocular sparks against blue backgrounds, particularly when copepods were present. A second experiment tested whether hungry fish showed more ocular sparks, which was not the case. However, background hue once more resulted in a significant differential use of ocular sparks. We conclude that iris radiance through ocular sparks in T. delaisi is not a side effect of eye movement, but adaptively modulated in response to the context under which prey are detected. We discuss the possible alternative functions of ocular sparks, including an as yet speculative role in active photolocation.