Artigos de revistas: "Transverse tubules"

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Jorgensen, A. O., W. Arnold, A. C. Shen, S. H. Yuan, M. Gaver e K. P. Campbell. "Identification of novel proteins unique to either transverse tubules (TS28) or the sarcolemma (SL50) in rabbit skeletal muscle." Journal of Cell Biology 110, n.º 4 (1 de abril de 1990): 1173–85. http://dx.doi.org/10.1083/jcb.110.4.1173.

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Novel proteins unique to either transverse tubules (TS28) or the sarcolemma (SL50) have been identified and characterized, and their in situ distribution in rabbit skeletal muscle has been determined using monoclonal antibodies. TS28, defined by mAb IXE112, was shown to have an apparent relative molecular mass of 28,000 D. Biochemical studies showed that TS28 is a minor membrane protein in isolated transverse tubular vesicles. Immunofluorescence and immunoelectron microscopical studies showed that TS28 is localized to the transverse tubules and in some subsarcolemmal vesicles possibly corresponding to the subgroup of caveolae connecting the transverse tubules with the sarcolemma. In contrast, TS28 is absent from the lateral portion of the sarcolemma. Immunofluorescence studies also showed that TS28 is more densely distributed in type II (fast) than in type I (slow) myofibers. Although TS28 and the 1,4-dihydropyridine receptor are both localized to transverse tubules and subsarcolemmal vesicles, TS28 is not a wheat germ agglutinin (WGA)-binding glycoprotein and does not appear to copurify with the 1,4-dihydropyridine receptor after detergent solubilization of transverse tubular membranes. SL50, defined by mAb IVD31, was shown to have an apparent relative molecular mass of 50,000 D. Biochemical studies showed that SL50 is not related to the 52,000-D (beta subunit) of the dihydropyridine receptor but does bind to WGA-Sepharose. Immunofluorescence labeling imaged by standard and confocal microscopy showed that SL50 is associated with the sarcolemma but apparently absent from the transverse tubules. Immunofluorescence labeling also showed that the density of SL50 in type II (fast) myofibers is indistinguishable from that of type I (slow) myofibers. The functions of TS28 and SL50 are presently unknown. However, the distinct distribution of TS28 to the transverse tubules and subsarcolemmal vesicles as determined by immunocytochemical labeling suggests that TS28 may be directly involved in excitation-contraction coupling. Our results demonstrate that, although transverse tubules are continuous with the sarcolemma, each of these membranes contain one or more unique proteins, thus supporting the idea that they each have a distinct protein composition.

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Dolber, P. C., R. P. Bauman, J. C. Rembert e J. C. Greenfield. "Regional changes in myocyte structure in model of canine right atrial hypertrophy". American Journal of Physiology-Heart and Circulatory Physiology 267, n.º 4 (1 de outubro de 1994): H1279—H1287. http://dx.doi.org/10.1152/ajpheart.1994.267.4.h1279.

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To investigate regional variation of myocyte response to atrial hypertrophy, control dogs were compared with dogs with right atrial hypertrophy created by induction of tricuspid regurgitation; after 1 yr, right atrial-to-body weight ratio increased 122% over controls. One section from the interatrial band, appendage and nonappendage roofs, and nonappendage side of each atrium of each dog was stained to reveal myocyte outlines and transverse tubules; myocyte cross-sectional areas were measured and transverse tubule prevalence was estimated. In control dogs, interatrial band myocytes were significantly larger and had more transverse tubules than other atrial myocytes. With atrial hypertrophy, right interatrial band myocytes did not increase significantly in size, whereas other right atrial myocytes nearly doubled in size, approaching the size of interatrial band myocytes without approaching the content of transverse tubules. Left atrial myocytes did not increase in size. Thus hypertrophic response of atrial myocytes to hemodynamic stress depends on the region in which the myocytes are found, and atrial hypertrophy does not demand transverse tubule proliferation.

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Dibb, Katharine M., William E. Louch e Andrew W. Trafford. "Cardiac Transverse Tubules in Physiology and Heart Failure". Annual Review of Physiology 84, n.º 1 (10 de fevereiro de 2022): 229–55. http://dx.doi.org/10.1146/annurev-physiol-061121-040148.

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In mammalian cardiac myocytes, the plasma membrane includes the surface sarcolemma but also a network of membrane invaginations called transverse (t-) tubules. These structures carry the action potential deep into the cell interior, allowing efficient triggering of Ca2+ release and initiation of contraction. Once thought to serve as rather static enablers of excitation-contraction coupling, recent work has provided a newfound appreciation of the plasticity of the t-tubule network's structure and function. Indeed, t-tubules are now understood to support dynamic regulation of the heartbeat across a range of timescales, during all stages of life, in both health and disease. This review article aims to summarize these concepts, with consideration given to emerging t-tubule regulators and their targeting in future therapies.

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Hong, TingTing, e Robin M. Shaw. "Cardiac T-Tubule Microanatomy and Function". Physiological Reviews 97, n.º 1 (janeiro de 2017): 227–52. http://dx.doi.org/10.1152/physrev.00037.2015.

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Unique to striated muscle cells, transverse tubules (t-tubules) are membrane organelles that consist of sarcolemma penetrating into the myocyte interior, forming a highly branched and interconnected network. Mature t-tubule networks are found in mammalian ventricular cardiomyocytes, with the transverse components of t-tubules occurring near sarcomeric z-discs. Cardiac t-tubules contain membrane microdomains enriched with ion channels and signaling molecules. The microdomains serve as key signaling hubs in regulation of cardiomyocyte function. Dyad microdomains formed at the junctional contact between t-tubule membrane and neighboring sarcoplasmic reticulum are critical in calcium signaling and excitation-contraction coupling necessary for beat-to-beat heart contraction. In this review, we provide an overview of the current knowledge in gross morphology and structure, membrane and protein composition, and function of the cardiac t-tubule network. We also review in detail current knowledge on the formation of functional membrane subdomains within t-tubules, with a particular focus on the cardiac dyad microdomain. Lastly, we discuss the dynamic nature of t-tubules including membrane turnover, trafficking of transmembrane proteins, and the life cycles of membrane subdomains such as the cardiac BIN1-microdomain, as well as t-tubule remodeling and alteration in diseased hearts. Understanding cardiac t-tubule biology in normal and failing hearts is providing novel diagnostic and therapeutic opportunities to better treat patients with failing hearts.

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5

Yuan, S., W. Arnold e A. O. Jorgensen. "Biogenesis of transverse tubules: immunocytochemical localization of a transverse tubular protein (TS28) and a sarcolemmal protein (SL50) in rabbit skeletal muscle developing in situ." Journal of Cell Biology 110, n.º 4 (1 de abril de 1990): 1187–98. http://dx.doi.org/10.1083/jcb.110.4.1187.

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To study the biogenesis of transverse tubules, the temporal appearance and distribution of TS28 (a specific marker of transverse tubules absent from the sarcolemma in adult skeletal muscle; 28,000 Mr) and SL50 (specifically associated with the sarcolemma and absent from the region of the transverse tubules in adult rabbit skeletal muscle) (Jorgensen, A.O., W. Arnold, A. C.-Y. Shen, S. Yuan, M. Gaver, and K.P. Campbell. 1990. J. Cell Biol. 110:1173-1185) were determined in rabbit skeletal muscle developing in situ (day 17 of gestation to day 15 newborn) by indirect immunofluorescence labeling. The results presented show that the temporal appearance and subcellular distribution of TS28 is distinct from that of SL50 at the developmental stages examined. TS28 was first detected in some, but not all, multinucleated myotubes on day 17 of gestation. At this stage of development, SL50 and the Ca2(+)-ATPase of the sarcoplasmic reticulum were already present in all myotubes. TS28 first appeared in discrete foci mostly confined to the cell periphery of the myotubes. At subsequent stages of development (days 19-24 of gestation), TS28 was also found in shoft finger-like structures extending obliquely and transversely from the cell periphery towards the center of the myotubes. 1-2 d after birth, TS28 was observed in an anastomosing network composed of transversely oriented chickenwire-like networks extending throughout the cytoplasm and interconnected by longitudinally oriented fiber-like structures. As development proceeded, the transversely oriented network became increasingly dominant. By day 10 of postnatal development, the longitudinally oriented component of the tubular network was not regularly observed. At none of the developmental stages examined was TS28 observed to be uniformly distributed at the cell periphery. SL50, like TS28, first appeared in discrete foci at the cell periphery. However, shortly after its first appearance it appeared to be distributed along the entire cell periphery. Although the intensity of SL50 labeling increased with development, it remained confined to the sarcolemma and was absent from the interior regions of the myofibers, where transverse tubules were present at all subsequent developmental stages examined. Immunoblotting of cell extracts from skeletal muscle tissue at various stages of development showed that SL50 was first detected on day 24 of gestation, while TS28 was not detected until days 1-2 after birth. Comparison of these results with previous ultrastructural studies of the formation of transverse tubules supports the idea that the temporal appearance and subcellular distribution of TS28 correspond very closely to that of the distribution of forming transverse tubules in rabbit skeletal muscle developing in situ.(ABSTRACT TRUNCATED AT 400 WORDS)

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Wang, W., P. A. Hansen, B. A. Marshall, J. O. Holloszy e M. Mueckler. "Insulin unmasks a COOH-terminal Glut4 epitope and increases glucose transport across T-tubules in skeletal muscle." Journal of Cell Biology 135, n.º 2 (15 de outubro de 1996): 415–30. http://dx.doi.org/10.1083/jcb.135.2.415.

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An improved immunogold labeling procedure was used to examine the subcellular distribution of glucose transporters in Lowricryl HM20-embedded skeletal muscle from transgenic mice overexpressing either Glut1 or Glut4. In basal muscle, Glut4 was highly enriched in membranes of the transverse tubules and the terminal cisternae of the triadic junctions. Less than 10% of total muscle Glut4 was present in the vicinity of the sarcolemmal membrane. Insulin treatment increased the number of gold particles associated with the transverse tubules and the sarcolemma by three-fold. However, insulin also increased the total Glut4 immunogold reactivity in muscle ultrathin sections by up to 1.8-fold and dramatically increased the amount of Glut4 in muscle sections as observed by laser confocal immunofluorescence microscopy. The average diameter of transverse tubules observed in longitudinal sections increased by 50% after insulin treatment. Glut1 was highly enriched in the sarcolemma, both in the basal state and after insulin treatment. Disruption of transverse tubule morphology by in vitro glycerol shock completely abolished insulin-stimulated glucose transport in isolated rat epitrochlearis muscles. These data indicate that: (a) Glut1 and Glut4 are targeted to distinct plasma membrane domains in skeletal muscle; (b) Glut1 contributes to basal transport at the sarcolemma and the bulk of insulin-stimulated transport is mediated by Glut4 localized in the transverse tubules; (c) insulin increases the apparent surface area of transverse tubules in skeletal muscle; and (d) insulin causes the unmasking of a COOH-terminal antigenic epitope in skeletal muscle in much the same fashion as it does in rat adipocytes.

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Richards, M. A., J. D. Clarke, P. Saravanan, N. Voigt, D. Dobrev, D. A. Eisner, A. W. Trafford e K. M. Dibb. "Transverse tubules are a common feature in large mammalian atrial myocytes including human". American Journal of Physiology-Heart and Circulatory Physiology 301, n.º 5 (novembro de 2011): H1996—H2005. http://dx.doi.org/10.1152/ajpheart.00284.2011.

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Transverse (t) tubules are surface membrane invaginations that are present in all mammalian cardiac ventricular cells. The apposition of L-type Ca2+ channels on t tubules with the sarcoplasmic reticulum (SR) constitutes a “calcium release unit” and allows close coupling of excitation to the rise in systolic Ca2+. T tubules are virtually absent in the atria of small mammals, and therefore Ca2+ release from the SR occurs initially at the periphery of the cell and then propagates into the interior. Recent work has, however, shown the occurrence of t tubules in atrial myocytes from sheep. As in the ventricle, Ca2+ release in these cells occurs simultaneously in central and peripheral regions. T tubules in both the atria and the ventricle are lost in disease, contributing to cellular dysfunction. The aim of this study was to determine if the occurrence of t tubules in the atrium is restricted to sheep or is a more general property of larger mammals including humans. In atrial tissue sections from human, horse, cow, and sheep, membranes were labeled using wheat germ agglutinin. As previously shown in sheep, extensive t-tubule networks were present in horse, cow, and human atrial myocytes. Analysis shows half the volume of the cell lies within 0.64 ± 0.03, 0.77 ± 0.03, 0.84 ± 0.03, and 1.56 ± 0.19 μm of t-tubule membrane in horse, cow, sheep, and human atrial myocytes, respectively. The presence of t tubules in the human atria may play an important role in determining the spatio-temporal properties of the systolic Ca2+ transient and how this is perturbed in disease.

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8

Stephenson, Elizabeth W. "Mechanisms of stimulated 45Ca efflux in skinned skeletal muscle fibers". Canadian Journal of Physiology and Pharmacology 65, n.º 4 (1 de abril de 1987): 632–41. http://dx.doi.org/10.1139/y87-106.

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Excitation–contraction (E–C) coupling in skeletal muscle can be studied in skinned fibers by direct assay of 45Ca efflux and simultaneous isometric force, under controlled conditions. Recent work provides evidence that such studies can address major current questions about the mechanisms of signal transmission between transverse tubules and sarcoplasmic reticulum and sarcoplasmic reticulum calcium release, as well as operation of the sarcoplasmic reticulum active Ca transport system in situ. Stimulation by imposed ion gradients at constant [K+][Cl−] product results in 45Ca release with two components: a large Ca2+-dependent efflux, responsible for contractile activation, and a small Ca2+-insensitive efflux. The Ca2+-insensitive stimulation is sustained, consistent with sustained depolarization, and appears to gradate the Ca2+-dependent stimulation; this component is likely to reflect intermediate steps in E–C coupling. Several lines of evidence suggest that the depolarizing stimulus acts on the transverse tubules. It is inhibited by the impermeant glycoside ouabain applied before skinning, which should specifically inhibit polarization of subsequently sealed transverse tubules. Sealed polarized transverse tubules also are the only plausible target for stimulation of 45Ca release by monensin and gramicidin D, which can rapidly dissipate Na+ and K+ gradients; a protonophore and the K+-specific ionophore valinomycin are ineffective, lonophore stimulation is prevented by the permeant glycoside digitoxin; it is also highly Ca2+ dependent. Stimulation of 45Ca release by imposed ion gradients is potentiated by perchlorate, which potentiates charge movements and activation in intact fibers, and is inhibited selectively in highly stretched fibers, presumably by transverse tubule – sarcoplasmic reticulum uncoupling. These results relate the Ca2+-dependent sarcoplasmic reticulum efflux channel to the physiological transverse tubule – sarcoplasmic reticulum coupling pathway, which also could involve Ca2+.

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Laflamme, Michael A., e Peter L. Becker. "Gs and adenylyl cyclase in transverse tubules of heart: implications for cAMP-dependent signaling". American Journal of Physiology-Heart and Circulatory Physiology 277, n.º 5 (1 de novembro de 1999): H1841—H1848. http://dx.doi.org/10.1152/ajpheart.1999.277.5.h1841.

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The transverse tubules are highly specialized invaginations of the cardiac sarcolemmal membrane involved in excitation-contraction (EC) coupling. Several proteins directly involved in EC coupling have been shown to reside either in the transverse tubular membrane or in closely associated structures. With the use of immunofluorescence microscopy, we have found that GS and adenylyl cyclase, key elements in the β-adrenergic signal transduction cascade, are essentially homogeneously distributed throughout the transverse tubular network of isolated rat ventricular myocytes. GS, in particular, was much more abundant within the transverse tubular membrane than in the peripheral sarcolemma. Furthermore, both proteins are also present in the intercalated disk region. The location of these elements of the cAMP-signaling cascade within a few micrometers of every inotropic target suggests that control and action of this second messenger are quite local. Furthermore, a similar distribution is likely for negatively inotropic receptor systems that oppose GS-linked receptors at the level of adenylyl cyclase. Thus, in addition to their role in EC coupling, transverse tubules appear to be the primary site for signaling by inotropic agents.

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Frisk, Michael, Jussi T. Koivumäki, Per A. Norseng, Mary M. Maleckar, Ole M. Sejersted e William E. Louch. "Variable t-tubule organization and Ca2+ homeostasis across the atria". American Journal of Physiology-Heart and Circulatory Physiology 307, n.º 4 (15 de agosto de 2014): H609—H620. http://dx.doi.org/10.1152/ajpheart.00295.2014.

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Although t-tubules have traditionally been thought to be absent in atrial cardiomyocytes, recent studies have suggested that t-tubules exist in the atria of large mammals. However, it is unclear whether regional differences in t-tubule organization exist that define cardiomyocyte function across the atria. We sought to investigate regional t-tubule density in pig and rat atria and the consequences for cardiomyocyte Ca2+ homeostasis. We observed t-tubules in approximately one-third of rat atrial cardiomyocytes, in both tissue cryosections and isolated cardiomyocytes. In a minority (≈10%) of atrial cardiomyocytes, the t-tubular network was well organized, with a transverse structure resembling that of ventricular cardiomyocytes. In both rat and pig atrial tissue, we observed higher t-tubule density in the epicardium than in the endocardium. Consistent with high variability in the distribution of t-tubules and Ca2+ channels among cells, L-type Ca2+ current amplitude was also highly variable and steeply dependent on capacitance and t-tubule density. Accordingly, Ca2+ transients showed great variability in Ca2+ release synchrony. Simultaneous imaging of the cell membrane and Ca2+ transients confirmed t-tubule functionality. Results from mathematical modeling indicated that a transmural gradient in t-tubule organization and Ca2+ release kinetics supports synchronization of contraction across the atrial wall and may underlie transmural differences in the refractory period. In conclusion, our results indicate that t-tubule density is highly variable across the atria. We propose that higher t-tubule density in cells localized in the epicardium may promote synchronization of contraction across the atrial wall.

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Kong, Cherrie H. T., Eva A. Rog-Zielinska, Peter Kohl, Clive H. Orchard e Mark B. Cannell. "Solute movement in the t-tubule system of rabbit and mouse cardiomyocytes". Proceedings of the National Academy of Sciences 115, n.º 30 (10 de julho de 2018): E7073—E7080. http://dx.doi.org/10.1073/pnas.1805979115.

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Cardiac transverse (t-) tubules carry both electrical excitation and solutes toward the cell center but their ability to transport small molecules is unclear. While fluorescence recovery after photobleaching (FRAP) can provide an approach to measure local solute movement, extraction of diffusion coefficients is confounded by cell and illumination beam geometries. In this study, we use measured cellular geometry and detailed computer modeling to derive the apparent diffusion coefficient of a 1-kDa solute inside the t-tubular system of rabbit and mouse ventricular cardiomyocytes. This approach shows that diffusion within individual t-tubules is more rapid than previously reported. T-tubule tortuosity, varicosities, and the presence of longitudinal elements combine to substantially reduce the apparent rate of solute movement. In steady state, large (>4 kDa) solutes did not freely fill the t-tubule lumen of both species and <50% of the t-tubule volume was available to solutes >70 kDa. Detailed model fitting of FRAP data suggests that solute diffusion is additionally restricted at the t-tubular entrance and this effect was larger in mouse than in rabbit. The possible structural basis of this effect was investigated using electron microscopy and tomography. Near the cell surface, mouse t-tubules are more tortuous and filled with an electron-dense ground substance, previously identified as glycocalyx and a polyanionic mesh. Solute movement in the t-tubule network of rabbit and mouse appears to be explained by their different geometric properties, which impacts the use of these species for understanding t-tubule function and the consequences of changes associated with t-tubule disease.

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Shepherd, Neal, e Holly B. McDonough. "Ionic diffusion in transverse tubules of cardiac ventricular myocytes". American Journal of Physiology-Heart and Circulatory Physiology 275, n.º 3 (1 de setembro de 1998): H852—H860. http://dx.doi.org/10.1152/ajpheart.1998.275.3.h852.

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We have estimated the rate of diffusion of calcium ions in the transverse tubules of isolated cardiocytes by recording changes in peak calcium current ( I Ca) caused by rapid changes of the extracellular calcium concentration ([Ca]o) at various intervals just preceding activation of I Ca. Isolated ventricular cells of guinea pig heart and atrial cells from rabbit heart were voltage-clamped (whole cell patch), superfused at a high flow rate, and stimulated continuously with depolarizing pulses (0.5 Hz, 200- or 20-ms pulses from a holding potential of −45 or −75 mV to 0 mV). In ventricular cells, the change in peak I Ca following a sudden change of [Ca]oincreased rapidly as the delay between the solution change and depolarization was increased, up to a delay of ∼75 ms [time constant (τ) ≈ 20 ms, 30–40% of total current change), and then increased more slowly (τ ≈ 200 ms, 60–70% of total current change); 400–500 ms were needed to achieve 90% of the total current increase. In atrial cells, a clear separation into two phases was not possible and 90% of the current change occurred within 85 ms. The slow phase of current change, which was unique to the ventricular cells, presumably reflects the slow equilibration of ions between the bulk perfusate and the lumina of the transverse tubules. If the lengths of the transverse tubules were equal to the cell thickness, the slow rate of change of current would be consistent with an apparent diffusion coefficient for calcium ions of 0.95 × 10−6cm2/s, considerably smaller than the value in bulk solution (7.9 × 10−6cm2/s). Most likely, this discrepancy is due to a high degree of tortuosity in the transverse tubular system in guinea pig ventricular cells or possibly to ion binding sites within the tubular membranes and glycocalyx.

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Harada, Hime, Katsumasa Yamashita e Toshitada Yoshioka. "Swelling of transverse tubules (T-tubules) resulting from reperfusion-induced arrythmias". Journal of Molecular and Cellular Cardiology 24 (maio de 1992): 53. http://dx.doi.org/10.1016/0022-2828(92)90185-3.

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Frank, J. S., G. Mottino, F. Chen, V. Peri, P. Holland e B. S. Tuana. "Subcellular distribution of dystrophin in isolated adult and neonatal cardiac myocytes". American Journal of Physiology-Cell Physiology 267, n.º 6 (1 de dezembro de 1994): C1707—C1716. http://dx.doi.org/10.1152/ajpcell.1994.267.6.c1707.

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The subcellular localization of dystrophin was examined in adult rabbit and rat cardiac myocytes with immunofluorescence and at higher resolution with immunogold. The aim was to resolve the conflicting reports on the presence of dystrophin in the transverse tubules (T tubules) of cardiac muscle and to determine its distribution in neonatal myocytes before and during the development of the T tubules. Dystrophin was localized to the peripheral sarcolemma and the T-tubular membrane and was absent from the intercalated disk membranes. In addition, dystrophin localization was followed with immunofluorescence in developing rabbit myocytes at 4 days, 1 wk, and 1 mo after birth. At 4 days of age, T tubules are absent and dystrophin was localized only in the peripheral sarcolemma. Dystrophin was present in the developing T tubules at 1 wk and 1 mo. These results imply that dystrophin is expressed in the T tubules as soon as they develop and confirm the different distribution of dystrophin in the T tubules of cardiac and skeletal muscle.

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Flucher, B. E., S. B. Andrews e M. P. Daniels. "Molecular organization of transverse tubule/sarcoplasmic reticulum junctions during development of excitation-contraction coupling in skeletal muscle." Molecular Biology of the Cell 5, n.º 10 (outubro de 1994): 1105–18. http://dx.doi.org/10.1091/mbc.5.10.1105.

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The relationship between the molecular composition and organization of the triad junction and the development of excitation-contraction (E-C) coupling was investigated in cultured skeletal muscle. Action potential-induced calcium transients develop concomitantly with the first expression of the dihydropyridine receptor (DHPR) and the ryanodine receptor (RyR), which are colocalized in clusters from the time of their earliest appearance. These DHPR/RyR clusters correspond to junctional domains of the transverse tubules (T-tubules) and sarcoplasmic reticulum (SR), respectively. Thus, at first contact T-tubules and SR form molecularly and structurally specialized membrane domains that support E-C coupling. The earliest T-tubule/SR junctions show structural characteristics of mature triads but are diverse in conformation and typically are formed before the extensive development of myofibrils. Whereas the initial formation of T-tubule/SR junctions is independent of association with myofibrils, the reorganization into proper triads occurs as junctions become associated with the border between the A band and the I band of the sarcomere. This final step in triad formation manifests itself in an increased density and uniformity of junctions in the cytoplasm, which in turn results in increased calcium release and reuptake rates.

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Gross, Polina, Jaslyn Johnson, Carlos M. Romero, Deborah M. Eaton, Claire Poulet, Jose Sanchez-Alonso, Carla Lucarelli et al. "Interaction of the Joining Region in Junctophilin-2 With the L-Type Ca 2+ Channel Is Pivotal for Cardiac Dyad Assembly and Intracellular Ca 2+ Dynamics". Circulation Research 128, n.º 1 (8 de janeiro de 2021): 92–114. http://dx.doi.org/10.1161/circresaha.119.315715.

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Rationale: Ca 2+ -induced Ca 2+ release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules) and RyR (ryanodine receptors) within the junctional sarcoplasmic reticulum. CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. JPH (junctophilin) 2 enables close association between T-tubules and the junctional sarcoplasmic reticulum to ensure efficient CICR. JPH2 has a so-called joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown. Objective: To determine if the joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR. Methods and Results: Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult feline and rat ventricular myocytes. Protein-protein interaction studies showed that the joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the joining region (mut PG1 JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mut PG1 JPH2 caused asynchronous Ca 2+ -release with impaired excitation-contraction coupling after β-adrenergic stimulation. The disturbed Ca 2+ regulation in mut PG1 JPH2 overexpressing myocytes caused calcium/calmodulin-dependent kinase II activation and altered myocyte bioenergetics. Conclusions: The interaction between LTCC and the joining region in JPH2 facilitates dyad assembly and maintains normal CICR in cardiomyocytes.

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Ferrantini, Cecilia, Raffaele Coppini, Leonardo Sacconi, Benedetta Tosi, Mei Luo Zhang, Guo Liang Wang, Ewout de Vries et al. "Impact of detubulation on force and kinetics of cardiac muscle contraction". Journal of General Physiology 143, n.º 6 (26 de maio de 2014): 783–97. http://dx.doi.org/10.1085/jgp.201311125.

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Action potential–driven Ca2+ currents from the transverse tubules (t-tubules) trigger synchronous Ca2+ release from the sarcoplasmic reticulum of cardiomyocytes. Loss of t-tubules has been reported in cardiac diseases, including heart failure, but the effect of uncoupling t-tubules from the sarcolemma on cardiac muscle mechanics remains largely unknown. We dissected intact rat right ventricular trabeculae and compared force, sarcomere length, and intracellular Ca2+ in control trabeculae with trabeculae in which the t-tubules were uncoupled from the plasma membrane by formamide-induced osmotic shock (detubulation). We verified disconnection of a consistent fraction of t-tubules from the sarcolemma by two-photon fluorescence imaging of FM4-64–labeled membranes and by the absence of tubular action potential, which was recorded by random access multiphoton microscopy in combination with a voltage-sensitive dye (Di-4-AN(F)EPPTEA). Detubulation reduced the amplitude and prolonged the duration of Ca2+ transients, leading to slower kinetics of force generation and relaxation and reduced twitch tension (1 Hz, 30°C, 1.5 mM [Ca2+]o). No mechanical changes were observed in rat left atrial trabeculae after formamide shock, consistent with the lack of t-tubules in rodent atrial myocytes. Detubulation diminished the rate-dependent increase of Ca2+-transient amplitude and twitch force. However, maximal twitch tension at high [Ca2+]o or in post-rest potentiated beats was unaffected, although contraction kinetics were slower. The ryanodine receptor (RyR)2 Ca-sensitizing agent caffeine (200 µM), which increases the velocity of transverse Ca2+ release propagation in detubulated cardiomyocytes, rescued the depressed contractile force and the slower twitch kinetics of detubulated trabeculae, with negligible effects in controls. We conclude that partial loss of t-tubules leads to myocardial contractile abnormalities that can be rescued by enhancing and accelerating the propagation of Ca2+-induced Ca2+ release to orphan RyR2 clusters.

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Ibrahim, Michael, Julia Gorelik, Magdi H. Yacoub e Cesare M. Terracciano. "The structure and function of cardiac t-tubules in health and disease". Proceedings of the Royal Society B: Biological Sciences 278, n.º 1719 (22 de junho de 2011): 2714–23. http://dx.doi.org/10.1098/rspb.2011.0624.

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The transverse tubules (t-tubules) are invaginations of the cell membrane rich in several ion channels and other proteins devoted to the critical task of excitation–contraction coupling in cardiac muscle cells (cardiomyocytes). They are thought to promote the synchronous activation of the whole depth of the cell despite the fact that the signal to contract is relayed across the external membrane. However, recent work has shown that t-tubule structure and function are complex and tightly regulated in healthy cardiomyocytes. In this review, we outline the rapidly accumulating knowledge of its novel roles and discuss the emerging evidence of t-tubule dysfunction in cardiac disease, especially heart failure. Controversy surrounds the t-tubules' regulatory elements, and we draw attention to work that is defining these elements from the genetic and the physiological levels. More generally, this field illustrates the challenges in the dissection of the complex relationship between cellular structure and function.

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19

Huang, C. L., e L. D. Peachey. "Anatomical distribution of voltage-dependent membrane capacitance in frog skeletal muscle fibers." Journal of General Physiology 93, n.º 3 (1 de março de 1989): 565–84. http://dx.doi.org/10.1085/jgp.93.3.565.

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Components of nonlinear capacitance, or charge movement, were localized in the membranes of frog skeletal muscle fibers by studying the effect of 'detubulation' resulting from sudden withdrawal of glycerol from a glycerol-hypertonic solution in which the muscles had been immersed. Linear capacitance was evaluated from the integral of the transient current elicited by imposed voltage clamp steps near the holding potential using bathing solutions that minimized tubular voltage attenuation. The dependence of linear membrane capacitance on fiber diameter in intact fibers was consistent with surface and tubular capacitances and a term attributable to the capacitance of the fiber end. A reduction in this dependence in detubulated fibers suggested that sudden glycerol withdrawal isolated between 75 and 100% of the transverse tubules from the fiber surface. Glycerol withdrawal in two stages did not cause appreciable detubulation. Such glycerol-treated but not detubulated fibers were used as controls. Detubulation reduced delayed (q gamma) charging currents to an extent not explicable simply in terms of tubular conduction delays. Nonlinear membrane capacitance measured at different voltages was expressed normalized to accessible linear fiber membrane capacitance. In control fibers it was strongly voltage dependent. Both the magnitude and steepness of the function were markedly reduced by adding tetracaine, which removed a component in agreement with earlier reports for q gamma charge. In contrast, detubulated fibers had nonlinear capacitances resembling those of q beta charge, and were not affected by adding tetracaine. These findings are discussed in terms of a preferential localization of tetracaine-sensitive (q gamma) charge in transverse tubule membrane, in contrast to a more even distribution of the tetracaine-resistant (q beta) charge in both transverse tubule and surface membranes. These results suggest that q beta and q gamma are due to different molecules and that the movement of q gamma in the transverse tubule membrane is the voltage-sensing step in excitation-contraction coupling.

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20

SONG, LONG-SHENG, SILVIA GUATIMOSIM, LETICIA GÓMEZ-VIQUEZ, ERIC A. SOBIE, ANDREW ZIMAN, HALI HARTMANN e W. J. LEDERER. "Calcium Biology of the Transverse Tubules in Heart". Annals of the New York Academy of Sciences 1047, n.º 1 (junho de 2005): 99–111. http://dx.doi.org/10.1196/annals.1341.009.

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Yarom, R., G. E. Morris, R. Froede e J. Schaper. "Myocardial dystrophin immunolocalization at sarcolemma and transverse tubules". Experientia 48, n.º 6 (junho de 1992): 614–16. http://dx.doi.org/10.1007/bf01920250.

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22

Kieval, R. S., R. J. Bloch, G. E. Lindenmayer, A. Ambesi e W. J. Lederer. "Immunofluorescence localization of the Na-Ca exchanger in heart cells". American Journal of Physiology-Cell Physiology 263, n.º 2 (1 de agosto de 1992): C545—C550. http://dx.doi.org/10.1152/ajpcell.1992.263.2.c545.

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We investigated the localization of the Na-Ca exchanger in fixed, isolated heart cells from rat and guinea pig using immunocytochemical methods with epifluorescence and confocal microscopy. We found that the Na-Ca exchanger is distributed throughout all membranes in contact with the extracellular space, including the sarcolemma, the transverse tubules (T-tubules), and the intercalated disks. Microscopic nonuniformities in the fluorescent labeling appear to reflect varying views of the membranes containing Na-Ca exchanger protein. Confocal thin-section imaging reveals a regular grid of discrete foci of fluorescence, which represent Na-Ca exchanger in T-tubules viewed en face. These foci are 1.80 +/- 0.01 microns apart from sarcomere to sarcomere and are aligned with the Z-line. Along each Z-line, these foci are spaced at 1.22 +/- 0.11-microns intervals. Longitudinal sections of the sarcolemma-T-tubule junction show a comblike appearance, with T-tubules extending inward from the heavily labeled sarcolemma. Our finding that the Na-Ca exchanger is widely distributed over the cell surface may provide further insight into the role of Na-Ca exchange in the heart.

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23

Toutant, M., J. Barhanin, J. Bockaert e B. Rouot. "G-proteins in skeletal muscle. Evidence for a 40 kDa pertussis-toxin substrate in purified transverse tubules". Biochemical Journal 254, n.º 2 (1 de setembro de 1988): 405–9. http://dx.doi.org/10.1042/bj2540405.

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In muscle, it has been established that guanosine 5′-[gamma-thio]triphosphate (GTP[S]), a non-hydrolysable GTP analogue, elicits a rise in tension in chemically skinned fibres, and that pretreatment with Bordetella pertussis toxin (PTX) decreases GTP[S]-induced tension development [Di Virgilio, Salviati, Pozzan & Volpe (1986) EMBO J. 5, 259-262]. In the present study, G-proteins were analysed by PTX-catalysed ADP-ribosylation and by immunoblotting experiments at cellular and subcellular levels. First, the nature of the G-proteins present in neural and aneural zones of rat diaphragm muscle was investigated. PTX, known to catalyse the ADP-ribosylation of the alpha subunit of several G-proteins, was used to detect G-proteins. Three sequential extractions (low-salt-soluble, detergent-soluble and high-salt-soluble) were performed, and PTX was found to label two substrates of 41 and 40 kDa only in the detergent-soluble fraction. The addition of pure beta gamma subunits of G-proteins to the low-salt-soluble extract did not provide a way to detect PTX-catalysed ADP-ribosylation of G-protein alpha subunits in this hydrophilic fraction. In neural as well as in aneural zones, the 39 kDa PTX substrate, very abundant in the nervous system (Go alpha), was not observed. We then studied the nature of the G alpha subunits present in membranes from transverse tubules (T-tubules) purified from rabbit skeletal muscle. Only one 40 kDa PTX substrate was found in T-tubules, known to be the key element of excitation-contraction coupling. The presence of a G-protein in T-tubule membranes was further confirmed by the immunoreactivity detected with an anti-beta-subunit antiserum. A 40 kDa protein was also detected in T-tubule membranes with an antiserum raised against a purified bovine brain Go alpha. The presence of two PTX substrates (41 and 40 kDa) in equal amounts in total muscle extracts, compared with only one (40 kDa) found in purified T-tubule membranes, suggests that this 40 kDa PTX substrate might be involved in excitation-contraction coupling.

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24

Dunn, S. M. "Voltage-dependent Calcium Channels in Skeletal Muscle Transverse Tubules". Journal of Biological Chemistry 264, n.º 19 (julho de 1989): 11053–60. http://dx.doi.org/10.1016/s0021-9258(18)60425-9.

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25

Flucher, Bernhard E., Mark Terasaki, Hemin Chin, Troy J. Beeler e Mathew P. Daniels. "Biogenesis of transverse tubules in skeletal muscle in vitro". Developmental Biology 145, n.º 1 (maio de 1991): 77–90. http://dx.doi.org/10.1016/0012-1606(91)90214-n.

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26

Crossman, D., X. Shen, M. Jüllig, D. Baddeley, P. Ruygrok e C. Soeller. "Fibrosis of the Transverse Tubules in human heart failure". Heart, Lung and Circulation 24 (2015): S206. http://dx.doi.org/10.1016/j.hlc.2015.06.226.

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27

Murphy, Brian J., e Balwant S. Tuana. "Calcium ions inhibit the allosteric interaction between the dihydropyridine and phenylalkylamine binding site on the voltage-gated calcium channel in heart sarcolemma but not in skeletal muscle transverse tubules". Canadian Journal of Physiology and Pharmacology 68, n.º 11 (1 de novembro de 1990): 1389–95. http://dx.doi.org/10.1139/y90-211.

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Calcium channel blockers bind with high affinity to sites on the voltage-sensitive Ca2+ channel. Radioligand binding studies with various Ca2+ channel blockers have facilitated identification and characterization of binding sites on the channel structure. In the present study we evaluated the relationship between the binding sites for the Ca2+ channel blockers on the voltage-sensitive Ca2+ channel from rabbit heart sarcolemma and rabbit skeletal muscle transverse tubules. [3H]PN200-110 binds with high affinity to a single population of sites on the voltage-sensitive Ca2+ channel in both rabbit heart sarcolemma and skeletal muscle transverse tubules. [3H]PN200-110 binding was not affected by added Ca2+ whereas EGTA and EDTA noncompetitively inhibited binding in both types of membrane preparations. EDTA was a more potent inhibitor of [3H]PN200-110 binding than EGTA. Diltiazem stimulates the binding of [3H]PN200-110 in a temperature-sensitive manner. Verapamil inhibited binding of [3H]PN200-110 to both types of membrane preparations in a negative manner, although this effect was of a complex nature in skeletal muscle transverse tubules. The negative effect of verapamil on [3H]PN200-110 binding in cardiac muscle was completely reversed by Ca2+. On the other hand, Ca2+ was without effect on the negative cooperativity seen between verapamil and [3H]PN200-110 binding in skeletal muscle transverse tubules. Since Ca2+ did not affect [3H]PN200-110 binding to membranes, we would like to suggest that Ca2+ is modulating the negative effect of verapamil on [3H]PN200-110 binding through a distinct Ca2+ binding site. The differential effect of Ca2+ on the negative cooperativity between verapamil and [3H]PN200-110 binding in rabbit heart and skeletal muscle membrane may reflect molecular and functional differences between voltage-sensitive Ca2+ channels in these two types of tissue.Key words: Ca2+ channel, sarcolemma, calcium channel blockers.

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28

Dombrowski, L., D. Roy, B. Marcotte e A. Marette. "A new procedure for the isolation of plasma membranes, T tubules, and internal membranes from skeletal muscle". American Journal of Physiology-Endocrinology and Metabolism 270, n.º 4 (1 de abril de 1996): E667—E676. http://dx.doi.org/10.1152/ajpendo.1996.270.4.e667.

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A new subcellular fractionation procedure for the simultaneous isolation of plasma membranes and transverse (T) tubule membranes from a rat skeletal muscle was developed. This new technique allows the isolation and separation of plasma membranes and T tubules in distinct subcellular fractions, as revealed by the membrane distribution of enzymatic and immunologic markers of both cell surface compartments. The procedure also yields a novel membrane fraction that is devoid of markers of both surface domains but is markedly enriched with GLUT-4 glucose transporters, thus strongly suggesting that it represents an intracellular pool of GLUT-4. Using this new procedure, we found that acute in vivo insulin administration (30 min) increased GLUT-4 protein content in the plasma membrane and a T tubule fraction (by approximately 80%), whereas a smaller elevation (35%) was observed in another fraction enriched with T tubules. Insulin induced a concomitant reduction (approximately 40%) in GLUT-4 abundance in the intracellular fraction. These results further support the hypothesis that T tubules are involved in the regulation of glucose transport in skeletal muscle. This novel fractionation method will be useful in investigating the regulation of muscle GLUT-4 transporters in other physiological and disease states such as diabetes, where defective translocation of the transporter protein to either one or both cell surface domains is suspected to occur.

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29

Crossman, David J., Xin Shen, Mia Jüllig, Michelle Munro, Yufeng Hou, Martin Middleditch, Darshan Shrestha et al. "Increased collagen within the transverse tubules in human heart failure". Cardiovascular Research 113, n.º 8 (20 de abril de 2017): 879–91. http://dx.doi.org/10.1093/cvr/cvx055.

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30

Dibb, Katharine M., Jessica D. Clarke, David A. Eisner, Mark A. Richards e Andrew W. Trafford. "A functional role for transverse (t-) tubules in the atria". Journal of Molecular and Cellular Cardiology 58 (maio de 2013): 84–91. http://dx.doi.org/10.1016/j.yjmcc.2012.11.001.

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Hagen, Brian M., Marcel A. Lauterbach, Eva Wagner, Stefan W. Hell, Stephan E. Lehnart e W. Jonathan Lederer. "Solute Transport in the Transverse Tubules of Cardiac Ventricular Myocytes". Biophysical Journal 98, n.º 3 (janeiro de 2010): 361a. http://dx.doi.org/10.1016/j.bpj.2009.12.1948.

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32

Hidalgo, Cecilia, M. Elena González e Ana M. García. "Calcium transport in transverse tubules isolated from rabbit skeletal muscle". Biochimica et Biophysica Acta (BBA) - Biomembranes 854, n.º 2 (janeiro de 1986): 279–86. http://dx.doi.org/10.1016/0005-2736(86)90121-5.

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Dohm, G. Lynis, Patricia L. Dolan, Wilhelm R. Frisell e Ronald W. Dudek. "Role of transverse tubules in insulin stimulated muscle glucose transport". Journal of Cellular Biochemistry 52, n.º 1 (maio de 1993): 1–7. http://dx.doi.org/10.1002/jcb.240520102.

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Parton, R. G., A. Carozzi e J. Gustavsson. "Caves and labyrinths: caveolae and transverse tubules in skeletal muscle". Protoplasma 212, n.º 1-2 (março de 2000): 15–23. http://dx.doi.org/10.1007/bf01279343.

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35

Sonoda, Masaki, Hideshige Moriya e Yutaka Shimada. "Intermediate voltage electron microscopy of transverse tubules at myotendinous junctions". Microscopy Research and Technique 24, n.º 5 (1 de abril de 1993): 423–28. http://dx.doi.org/10.1002/jemt.1070240507.

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Quinn, Callum, Yatong Li, Andrew Trafford e Katharine Dibb. "Understanding the relationship between dysferlin, transverse (t)-tubules & arrhythmias". Journal of Molecular and Cellular Cardiology 173 (dezembro de 2022): 82. http://dx.doi.org/10.1016/j.yjmcc.2022.08.164.

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37

Fill, M. D., e P. M. Best. "Block of contracture in skinned frog skeletal muscle fibers by calcium antagonists." Journal of General Physiology 93, n.º 3 (1 de março de 1989): 429–49. http://dx.doi.org/10.1085/jgp.93.3.429.

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The ability of a number of calcium antagonistic drugs including nitrendipine, D600, and D890 to block contractures in single skinned (sarcolemma removed) muscle fibers of the frog Rana pipiens has been characterized. Contractures were initiated by ionic substitution, which is thought to depolarize resealed transverse tubules in this preparation. Depolarization of the transverse tubules is the physiological trigger for the release of calcium ion from the sarcoplasmic reticulum and thus of contractile protein activation. Since the transverse tubular membrane potential cannot be measured in this preparation, tension development is used as a measure of activation. Once stimulated, fibers become inactivated and do not respond to a second stimulus unless allowed to recover or reprime (Fill and Best, 1988). Fibers exposed to calcium antagonists while fully inactivated do not recover from inactivation (became blocked or paralyzed). The extent of drug-induced block was quantified by comparing the height of individual contractures. Reprimed fibers were significantly less sensitive to block by both nitrendipine (10 degrees C) and D600 (10 and 22 degrees C) than were inactivated fibers. Addition of D600 to fibers recovering from inactivation stopped further recovery, confirming preferential interaction of the drug with the inactivated state. A concerted model that assumed coupled transitions of independent drug-binding sites from the reprimed to the inactivated state adequately described the data obtained from reprimed fibers. Photoreversal of drug action left fibers inactivated even though the drug was initially added to fibers in the reprimed state. This result is consistent with the prediction from the model. The estimated KI for D600 (at 10 degrees and 22 degrees C) and for D890 (at 10 degrees C) was approximately 10 microM. The estimated KI for nitrendipine paralysis of inactivated fibers at 10 degrees C was 16 nM. The sensitivity of reprimed fibers to paralysis by D600 and D890 was similar. However, inactivated fibers were significantly less sensitive to the membrane-impermeant derivative (D890) than to the permeant species (D600), which suggests a change in the drug-binding site or its environment during the inactivation process. The enantomeric dihydropyridines (+) and (-) 202-791, reported to be calcium channel agonists and antagonists, respectively, both caused paralysis, which suggests that blockade of a transverse tubular membrane calcium flux is not the mechanism responsible for antagonist-induced paralysis. The data support a model of excitation-contraction coupling involving transverse tubular proteins that bind calcium antagonists.

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38

Jorgensen, A. O., A. C. Shen, W. Arnold, A. T. Leung e K. P. Campbell. "Subcellular distribution of the 1,4-dihydropyridine receptor in rabbit skeletal muscle in situ: an immunofluorescence and immunocolloidal gold-labeling study." Journal of Cell Biology 109, n.º 1 (1 de julho de 1989): 135–47. http://dx.doi.org/10.1083/jcb.109.1.135.

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The subcellular distribution of the 1,4-dihydropyridine receptor was determined in rabbit skeletal muscle in situ by immunofluorescence and immunoelectron microscopy. Longitudinal and transverse cryosections (5-8 microns) of rabbit gracilis muscle were labeled with monoclonal antibodies specific against either the alpha 1-subunit (170,000-D polypeptide) or the beta-subunit (52,000-D polypeptide) of the 1,4-dihydropyridine receptor by immunofluorescence labeling. In longitudinal sections, specific labeling was present only near the interface between the A- and I-band regions of the sarcomeres. In transverse sections, specific labeling showed a hexagonal staining pattern within each myofiber however, the relative staining intensity of the type II (fast) fibers was judged to be three- to fourfold higher than that of the type I (slow) fibers. Specific immunofluorescence labeling of the sarcolemma was not observed in either longitudinal or transverse sections. These results are consistent with the idea that the alpha 1-subunit and the beta-subunit of the purified 1,4-dihydropyridine receptor are densely distributed in the transverse tubular membrane. Immunoelectron microscopical localization with a monoclonal antibody to the alpha 1-subunit of the 1,4-dihydropyridine receptor showed that the 1,4-dihydropyridine receptor is densely distributed in the transverse tubular membrane. Approximately half of these were distributed in close proximity to the junctional region between the transverse tubules and the terminal cisternae. Specific labeling was also present in discrete foci in the subsarcolemmal region of the myofibers. The size and the nonrandom distribution of these foci in the subsarcolemmal region support the possibility that they correspond to invaginations from the sarcolemma called caveolae. In conclusion, our results demonstrate that the 1,4-dihydropyridine receptor in skeletal muscle is localized to the transverse tubular membrane and discrete foci in the subsarcolemmal region, possibly caveolae but absent from the lateral portion of the sarcolemma.

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39

Volpe, P., e E. W. Stephenson. "Ca2+ dependence of transverse tubule-mediated calcium release in skinned skeletal muscle fibers." Journal of General Physiology 87, n.º 2 (1 de fevereiro de 1986): 271–88. http://dx.doi.org/10.1085/jgp.87.2.271.

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Isometric force and 45Ca efflux from the sarcoplasmic reticulum were measured at 19 degrees C in frog skeletal muscle fibers skinned by microdissection. After Ca2+ loading, application of the ionophores monensin, an Na+(K+)/H+ exchanger, or gramicidin D, an H+ greater than K+ greater than Na+ channel-former, evoked rapid force development and stimulated release of approximately 30% of the accumulated 45Ca within 1 min, whereas CCCP (carbonyl cyanide pyruvate p-trichloromethoxyphenylhydrazone), a protonophore, and valinomycin, a neutral, K+-specific ionophore, did not. When monensin was present in all bathing solutions, i.e., before and during Ca2+ loading, subsequent application failed to elicit force development and to stimulate 45Ca efflux. 5 min pretreatment of the skinned fibers with 50 microM digitoxin, a permeant glycoside that specifically inhibits the Na+,K+ pump, inhibited monensin and gramicidin D stimulation of 45Ca efflux; similar pretreatment with 100 microM ouabain, an impermeant glycoside, was ineffective. Monensin stimulation of 45Ca efflux was abolished by brief pretreatment with 5 mM EGTA, which chelates myofilament-space calcium. These results suggest that: monensin and gramicidin D stimulate Ca2+ release from the sarcoplasmic reticulum that is mediated by depolarization of the transverse tubules, which seal off after sarcolemma removal and form closed compartments; a transverse tubule membrane potential (myofilament space-negative) is maintained and/or established by the operation of the Na+,K+ pump in the transverse tubule membranes and is sensitive to the permeant inhibitor digitoxin; the transverse tubule-mediated stimulation of 45Ca efflux appears to be entirely Ca2+ dependent.

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40

O'Connell, Kristen M. S., Jennifer D. Whitesell e Michael M. Tamkun. "Localization and mobility of the delayed-rectifer K+ channel Kv2.1 in adult cardiomyocytes". American Journal of Physiology-Heart and Circulatory Physiology 294, n.º 1 (janeiro de 2008): H229—H237. http://dx.doi.org/10.1152/ajpheart.01038.2007.

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The delayed-rectifier voltage-gated K+ channel (Kv) 2.1 underlies the cardiac slow K+ current in the rodent heart and is particularly interesting in that both its function and localization are regulated by many stimuli in neuronal systems. However, standard immunolocalization approaches do not detect cardiac Kv2.1; therefore, little is known regarding its localization in the heart. In the present study, we used recombinant adenovirus to determine the subcellular localization and lateral mobility of green fluorescent protein (GFP)-Kv2.1 and yellow fluorescent protein-Kv1.4 in atrial and ventricular myocytes. In atrial myocytes, Kv2.1 formed large clusters on the cell surface similar to those observed in hippocampal neurons, whereas Kv1.4 was evenly distributed over both the peripheral sarcolemma and the transverse tubules. However, fluorescence recovery after photobleach (FRAP) experiments indicate that atrial Kv2.1 was immobile, whereas Kv1.4 was mobile (τ = 252 ± 42 s). In ventricular myocytes, Kv2.1 did not form clusters and was localized primarily in the transverse-axial tubules and sarcolemma. In contrast, Kv1.4 was found only in transverse tubules and sarcolemma. FRAP studies revealed that Kv2.1 has a higher mobility in ventricular myocytes (τ = 479 ± 178 s), although its mobility is slower than Kv1.4 (τ1 = 18.9 ± 2.3 s; τ2 = 305 ± 55 s). We also observed the movement of small, intracellular transport vesicles containing GFP-Kv2.1 within ventricular myocytes. These data are the first evidence of Kv2.1 localization in living myocytes and indicate that Kv2.1 may have distinct physiological roles in atrial and ventricular myocytes.

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Robu, Valentin G., Emily S. Pfeiffer, Seth L. Robia, Ravi C. Balijepalli, YeQing Pi, Timothy J. Kamp e Jeffery W. Walker. "Localization of Functional Endothelin Receptor Signaling Complexes in Cardiac Transverse Tubules". Journal of Biological Chemistry 278, n.º 48 (12 de setembro de 2003): 48154–61. http://dx.doi.org/10.1074/jbc.m304396200.

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Wagner, Eva, Marcel Lauterbach, Volker Westphal, Brian Hagen, W. J. Lederer, Stefan W. Hell e Stephan E. Lehnart. "Sted Based Super-Resolution Imaging of Transverse Tubules in Ventricular Myocytes". Biophysical Journal 98, n.º 3 (janeiro de 2010): 5a. http://dx.doi.org/10.1016/j.bpj.2009.12.034.

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Rajagopal, Vijay, Isuru D. Jayasinghe e Christian Soeller. "Modelling the Structure and Function of Cardiac Cell Transverse-Axial-Tubules". Biophysical Journal 100, n.º 3 (fevereiro de 2011): 293a. http://dx.doi.org/10.1016/j.bpj.2010.12.1801.

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McNary, Thomas G., Kenneth W. Spitzer, John H. B. Bridge, Hilary Holloway, Peter Kohl e Frank B. Sachse. "Geometric Changes of Transverse Tubules in Rabbit Cardiac Myocytes during Contraction". Biophysical Journal 102, n.º 3 (janeiro de 2012): 356a. http://dx.doi.org/10.1016/j.bpj.2011.11.1947.

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45

Donoso, Paulina, e Cecilia Hidalgo. "Sodium-calcium exchange in transverse tubules isolated from frog skeletal muscle". Biochimica et Biophysica Acta (BBA) - Biomembranes 978, n.º 1 (janeiro de 1989): 8–16. http://dx.doi.org/10.1016/0005-2736(89)90491-4.

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Romer, Shannon H., Melissa Bautista, Daniel E. Hutcherson, Robert J. Talmadge e Andrew A. Voss. "Architecture of Transverse Tubules and Triads in Huntington's Disease Skeletal Muscle". Biophysical Journal 114, n.º 3 (fevereiro de 2018): 469a. http://dx.doi.org/10.1016/j.bpj.2017.11.2583.

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47

Horgan, Douglas J., e Ronald Kuypers. "Biochemical properties of purified transverse tubules isolated from skeletal muscle triads". Archives of Biochemistry and Biophysics 260, n.º 1 (janeiro de 1988): 1–9. http://dx.doi.org/10.1016/0003-9861(88)90417-1.

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Brandt, Neil R., e Anthony H. Caswell. "Localization of Mitsugumin 29 to Transverse Tubules in Rabbit Skeletal Muscle". Archives of Biochemistry and Biophysics 371, n.º 2 (novembro de 1999): 348–50. http://dx.doi.org/10.1006/abbi.1999.1444.

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Rasmussen, Hanne Borger, Morten Møller, Hans-Günther Knaus, Bo Skaaning Jensen, Søren-Peter Olesen e Nanna Koschmieder Jørgensen. "Subcellular localization of the delayed rectifier K+ channels KCNQ1 and ERG1 in the rat heart". American Journal of Physiology-Heart and Circulatory Physiology 286, n.º 4 (abril de 2004): H1300—H1309. http://dx.doi.org/10.1152/ajpheart.00344.2003.

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In the heart, several K+ channels are responsible for the repolarization of the cardiac action potential, including transient outward and delayed rectifier K+ currents. In the present study, the cellular and subcellular localization of the two delayed rectifier K+ channels, KCNQ1 and ether- a- go- go-related gene-1 (ERG1), was investigated in the adult rat heart. Confocal immunofluorescence microscopy of atrial and ventricular cells revealed that whereas KCNQ1 labeling was detected in both the peripheral sarcolemma and a structure transversing the myocytes, ERG1 immunoreactivity was confined to the latter. Immunoelectron microscopy of atrial and ventricular myocytes showed that the ERG1 channel was primarily expressed in the transverse tubular system and its entrance, whereas KCNQ1 was detected in both the peripheral sarcolemma and in the T tubules. Thus, whereas ERG1 displays a very restricted subcellular localization pattern, KCNQ1 is more widely distributed within the cardiac cells. The localization of these K+ channels to the transverse tubular system close to the Ca2+ channels renders them with maximal repolarizing effect.

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50

Jones, Sandra A., Michael J. Morton, Malcolm Hunter e Mark R. Boyett. "Expression of TASK-1, a pH-sensitive twin-pore domain K+ channel, in rat myocytes". American Journal of Physiology-Heart and Circulatory Physiology 283, n.º 1 (1 de julho de 2002): H181—H185. http://dx.doi.org/10.1152/ajpheart.00963.2001.

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We have investigated the expression of TASK-1, a pH-sensitive, twin-pore domain K+channel in the rat heart. A mammalian cell line of Chinese hamster ovary cells (CHO), transfected with a plasmid containing mouse TASK-1, demonstrated the specificity of the anti-TASK-1 antibody. TASK-1 expression in cardiac tissue was initially demonstrated by Western blot and then localized by immunofluorescence. In single rat ventricular myocytes, strong staining of the TASK-1 protein was located at the intercalated disks and across the cell in a striated pattern, corresponding to the transverse axial tubular network (T tubules). In contrast, single rat atrial myocytes were stained at the intercalated disks with a weak punctate, striated pattern corresponding to underdeveloped T tubules. Also, formamide was used to induce the detubulation of ventricular myocytes, which enabled confirmation that TASK-1 protein expression occurs in T tubules. Consistent with this, RT-PCR revealed the expression of TASK-1 mRNA in total RNA from both the ventricles and atria. In this study, we conclusively demonstrated that TASK-1 protein and mRNA were expressed in rat atrial and ventricular tissue. The extensive distribution of TASK-1 shown to exist within myocyte membranes may provide a potential future target for antiarrhythmic drugs.

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