Dissertations / Theses: 'Channel selectivity'

1

Ranatunga, Kishani M. "Computational studies of ion channel permeation and selectivity." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325774.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Livesey, Matthew Robert. "Molecular determinants of single channel conductance and ion selectivity in cationic Cys-loop receptor channels." Thesis, University of Dundee, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510623.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Thomson, Andrew Shane. "Voltage-dependent gating at the selectivity filter of the MthK K+ channel." Diss., Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/214824.

Full text

Abstract:

Biochemistry
Ph.D.
Voltage-dependent K+ channels can undergo a gating process known as C-type inactivation. This type of gating consists of entry into a nonconducting state that may involve conformational changes near the channel's selectivity filter. However, the details of the underlying mechanisms are not clear. Here, I report on a form of voltage-dependent inactivation gating observed in MthK, a prokaryotic K+ channel that lacks a canonical voltage sensor. In single-channel recordings, I observed that open probability (Po) decreases with depolarization, with a half-maximal voltage of 96 ± 3 mV. This gating is kinetically distinct from blockade by internal Ca2+ or Ba2+, suggesting that it may arise from an intrinsic inactivation mechanism. Inactivation gating was shifted toward more positive voltages by increasing external [K+] (47 mV per 10-fold increase in [K+]), suggesting that K+ binding at the extracellular side of the channel stabilizes the open-conductive state. The open-conductive state was stabilized by other external cations, and selectivity of the stabilizing site followed the sequence: K+ ≈ Rb+ > Cs+ > Na+ > Li+ ≈ NMG+. Selectivity of the stabilizing site is somewhat weaker than that of sites that determine permeability of these ions, consistent with the idea that the site may lie toward the external end of the MthK selectivity filter. MthK gating was described over a wide range of positive voltages and external [K+] using kinetic schemes in which the open-conductive state is stabilized by K+ binding to a site that is not deep within the electric field, with the voltage-dependence of inactivation arising from both voltage-dependent K+ dissociation and transitions between nonconducting (inactivated) states. Studies of C-type inactivation in voltage-gated K+ channels have demonstrated that inactivation can be enhanced by quaternary ammonium (QA) derivatives, which block current through the channel by binding to a site at the cytoplasmic side of the pore. Enhancement of inactivation is thought to occur through a mechanism in which QA blockade leads to depletion of K+ ions in the pore, thus driving the channel toward the inactivated state. I tested this model by using divalent cations to block the current through the MthK channel, and then quantifying the effects on inactivation. I observed that the voltage-dependence of blockade by Ca2+, Mg2+, and Sr2+ was approximately equal (zδ ≈ 0.4 e0 for blockade by each of the divalent cations), suggesting a similar location for the site of blockade. However, Ca2+ and Sr2+ were found to enhance inactivation, whereas Mg2+ does not. Molecular dynamics (MD) simulations suggested that Ca2+ and Sr2+ bind to a site (S5) closer to the selectivity filter than Mg2+, consistent with the idea that binding of a divalent cation to S5 enhances inactivation; the bound cation may in turn electrostatically interact with K+ ions in the selectivity filter to break the K+ conduction cycle. Previous studies on inactivation in KcsA have identified a critical residue involved in the mechanism of C-type inactivation in this channel. This residue, E71, is located in a region known as the pore helix, and is involved in a hydrogen bonding network involving a tryptophan residue also in the pore helix, as well as an aspartic acid residue in the selectivity filter, which drives the channel toward the inactivated state. However, mutation to alanine breaks the hydrogen bonding network and effectively prevents inactivation. To determine whether a similar mechanism may enhance inactivation in MthK, I performed mutagenesis at the MthK residue analogous to KcsA E71 (V55). In single channel recordings, I observed that mutation to glutamate (V55E) destabilized the open state of the channel, consistent with the idea that a hydrogen bonding network that drives the channel toward the inactivated state may be formed in MthK to enhance inactivation, similar to the mechanism proposed for KcsA. These results, along with previous findings, suggest that inactivation gating is linked to the selectivity filter of the channel. In most K+ selective channels, the selectivity filter is composed of a sequence of highly-conserved residues (TVGYG). Within this sequence, the sidechain of the conserved threonine residue determines the entry to the selectivity filter, and may thus be a key regulator of the K+ conduction cycle. Interestingly, the rapidly inactivating voltage-gated K+ channel, HERG, contains a serine at this position instead of a threonine. To determine the impact of a change from threonine to serine, I quantified effects of the mutation T59S in MthK on conduction and inactivation, and further probed these effects using blockade by divalent cations. I observed that this mutation reduces channel conductance and enhances inactivation, compared to the wild type channel, and enhanced blockade by Sr2+. MD simulations suggested an increased energy barrier for K+ ions to enter the selectivity filter, which may account for the decreased conductance. In addition, the serine sidechain may effect a redistribution of K+ within the selectivity filter, which may impact stability of the conducting state. Overall, my results suggest that several mechanisms contribute to K+ channel inactivation, involving a combination of ion-ion interactions in the pore, structural interactions among residues in the selectivity filter that may affect the stability of the conducting state, and interactions between ions and a key sidechain at the entry to the selectivity filter. Further understanding of these components of the inactivation process may provide a clearer picture of the mechanisms that generate diversity in gating properties among K+ channels.
Temple University--Theses

APA, Harvard, Vancouver, ISO, and other styles

4

Bukovnik, Urska. "Biophysical studies of m2glyr modified sequences: The effect of electrostatics on ion channel selectivity." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/13101.

Full text

Abstract:

Doctor of Philosophy
Department of Biochemistry
John M. Tomich
Channel replacement therapy represents a new treatment modality that could augment existing therapies against cystic fibrosis. It is based on designing synthetic channel-forming peptides (CFPs) with desirable selectivity, high ion transport rates and overall ability to supersede defective endogenous chloride channels. We derived synthetic CFPs from a peptide initially reconstituted from the second transmembrane segment of the α-subunit of Glycine receptor (M2GlyR). Our best candidate peptide NK4-M2GlyR T19R, S22W (p22-T19R, S22W) is soluble in aqueous solutions, has the ability to deliver itself to the epithelial cell membranes without the use of a delivery system, is non-immunogenic, but when assembled into a pore, lacks the structural properties for anion selectivity. Previous findings suggested that threonine residues at positions 13, 17 and 20 line the pore of assembled p22-T19R, S22W and recent studies indicated that an introduction of positively charged 2, 3-diaminopropionic acid (Dap) at either T13 or T17 in the sequence increases transepithelial ion transport rates across the apical membranes of Madin-Darby canine kidney (MDCK) epithelial cells. This study focused on further structural modifications of the pore-lining interface of p22-T19R, S22W assembled pore. It was hypothesized that singly, doubly or triply introduced Dap residues modify the pore geometry and that their positively charged side chains impact discrimination for anions. Dap-substituted p22-T19R, S22W peptides retain the α-helical secondary structure characteristic for their parent p22-T19R, S22W. The sequences containing multiple Dap-substituted residues induce higher short circuit current across the epithelial MDCK cells compared to peptides with single Dap-substitutions or no Dap-substitutions. Whole-cell voltage clamp recordings using Xenopus oocytes indicate that Dap-substituted peptide assemblies induce higher levels of voltage-dependent but non-selective ion current relative to p22-T19R, S22W. Studies using the D-enantiomer of p22-T19R, S22W and shorter truncated sequences of a full length L-p22-T19R, S22W and L-Dap-substituted peptides provided evidence that peptide-induced ion transport rates can be attributed to formation of de novo pathways. Results of preliminary computer modeling studies indicate that Dap residues affect the pore geometry but not ion selectivity. Future studies focusing on modifying the existing electrostatic environment towards anion selectivity will focus on staggering the charged residues of Dap at various locations inside synthetic pores.

APA, Harvard, Vancouver, ISO, and other styles

5

Lam, Andy Ka Ming. "Electrophysiological characterization of the human two-pore channel 2." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:3a16d16e-f692-40d7-87f7-920151896038.

Full text

Abstract:

The Two-pore channel (TPC1-3) family represents a recently identified class of endolysosomal ion channels. TPCs were originally proposed to be promising candidate channels for NAADP-induced Ca²⁺ release. However, subsequent studies have emerged to propose an alternative view where TPCs may be Na+-selective channels regulated by the lysosome-specific phosphoinositide PI(3,5)P2 or voltage in an isoform-dependent manner. This thesis asks the question of whether pharmacological and ion permeation properties of TPCs, in particular the human TPC2, may satisfy or may be consistent with the requirement of a potential NAADP-sensitive Ca²⁺-release channel. These fundamental properties of hTPC2 were approached using patch-clamp electrophysiology and confocal fluorescence microscopy, and were analysed quantitatively to extract relevant physical parameters important to our understanding of their physiological and functional significance. Chapter 2 presents the basic electrophysiological characterisation of hTPC2. It follows a logical way by first determining the ion permeation properties, followed by the investigation of its physical relation with fractional Ca²⁺ current and Ca²⁺ nanodomains to rigorously prove that this Na⁺ selectivity is sufficient to ensure negligible Ca²⁺ leakage both experimentally and theoretically. This follows the logic that matter must not be created nor destroyed so that a Na+-selective channel that poses a physiologically significant energy barrier to Ca²⁺ permeation from one side would not lead to the creation of Ca²⁺ on the other side. Chapter 3 represents a natural progression from Chapter 2 and is aimed at investigating the underlying mechanisms responsible for the electrophysiological ion selectivity observed. This chapter also follows a logical way by first identifying spermine as a high valence intracellular blocker, its mutual antagonism with different external ionic species that allows the determination of ion-binding affinity, followed by the determination of the concentration dependence of ion conduction to identify possible lower affinity binding. By considering all the above qualities, the outcome is a coherent description and connection of ion binding selectivity, kinetic selectivity and ion binding configuration with the observed electrophysiological selectivity. Chapter 4 discusses the missing puzzles and how these questions might be addressed.

APA, Harvard, Vancouver, ISO, and other styles

6

Firth, Jahn Michael. "Structural mechanisms of gating at the selectivity filter of the human cardiac ryanodine receptor (hRyR2) channel." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/89098/.

Full text

Abstract:

The cardiac ryanodine receptor (RyR2) contains structural elements within the channel pore that function as gates to regulate the release of intracellular calcium, initiating cardiac muscle contraction. The precise regulation of these gates is critical in maintaining normal cardiac function, and channel dysfunction, resulting in altered calcium handling, underlies the mechanisms of arrhythmia and sudden cardiac death. The enormous size of RyR2 has impeded the gathering of detailed structural information, hence the structural determinants for channel gating remain unknown. Structural modelling studies have revealed similarities between the RyR2 pore and the K+ channel, KcsA, providing a framework in which to test channel gating mechanisms. A region termed the selectivity filter is a gating component in K+ channels, involved in inactivation and flicker closings, and its conformation is maintained by a transient hydrogen-bonding network. This project examined the role of the RyR2 selectivity filter in channel gating by generating mutants at analogous positions to KcsA that either disrupted (Y4813A, D4829A and Y4839A) or maintained (Y4813W, D4829E and Y4839W) a proposed hydrogen-bonding network, and assessed their intracellular Ca2+ release, ryanodine modification and biophysical properties. Y4813A and D4829A had drastic effects on channel function, whereas retaining physicochemical properties of conservative mutations, Y4813W and Y4839W, maintained the functional characteristics of WT RyR2. Flicker closings were affected by Y4839A mutation however, in general, single-channel gating for Y4813W, Y4839A and Y4839W was comparable to WT RyR2. Interestingly, monitoring single-channels for prolonged periods revealed novel insights into channel behaviour, characterised by inherent fluctuations in channel activity under steady-state conditions. This thesis reveals that the selectivity filter region is an important component for RyR2 channel function. However, it remains unclear whether the selectivity filter regulates channel gating, as the proposed hydrogen-bonding network would not be possible due to altered residue distances revealed from recent high-resolution RyR structural models.

APA, Harvard, Vancouver, ISO, and other styles

7

Abrams, Christopher John. "Studies of the molecular basis of selectivity and gating in the inward rectifier potassium channel Kir2.1." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/29921.

Full text

Abstract:

1. The molecular basis of selectivity and gating were investigated in wild-type and mutant forms of the inward rectifier K+ channel Kir2.1 (IRK1). 2. Kir2.1 channels show characteristic time-dependent gating kinetics due to a reversible voltage-dependent channel block by cytoplasmic polyamines. Mutations at Asp 172 in the M2 domain revealed that a negative charge at this position is the main criterion of time-dependent gating kinetics in Kir2.1. 3. Kir channels are blocked by Cs+ and Rb+ in a voltage-dependent manner, characteristic of many Kir channels. Rb+ and Cs+ block in Kir2.1 was abolished by replacing Asp 172 by Asn, but was re-established by a change to Gln, narrowing the pore. However, blocking affinity was reduced by the mutation to Gln. 4. When Asp 172 was mutated to Glu, narrowing the pore but retaining the negative charge, block by both Cs+ and Rb+ was increased relative to wild-type. 5. Replacing Gly 168 in M2 by Ala was suggested to widen the pore at position 172. The effect of this mutation on Cs+ and Rb+ block was relatively small. 6. There appears to be a balance between charge and pore size in determining whether icons block or permeate. A major part of the selectivity of Kir2.1 is associated with Asp 172 in the M2 domain. This site also determines the time-dependent activation gating of the channel. 7. Mutation of Asp 172 to Ser were predicted to abolish both Cs+ and Rb+ block in Kir2.1, but blocking affinity was similar to WT. Therefore, other properties of the pore must contribute to Cs+ and Rb+ block at position 172 in addition to the electrostatic and steric effects identified in this study.

APA, Harvard, Vancouver, ISO, and other styles

8

Mikušević, Vedrana [Verfasser], Inga [Akademischer Betreuer] Hänelt, Inga [Gutachter] Hänelt, and Klaus [Gutachter] Fendler. "Ion selectivity of the unusual K+ channel KtrAB / Vedrana Mikušević ; Gutachter: Inga Hänelt, Klaus Fendler ; Betreuer: Inga Hänelt." Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2020. http://d-nb.info/1212930231/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Moffat, Jeffrey C. "Properties of Conductance and Inhibition of Proton Channels: M2 from Influenza A Virus and Fo from Escherichia coli ATP Synthase." BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/479.

Full text

Abstract:

Proton channels are essential for many of the processes of life. The influenza A viral protein M2 is responsible for sensing the conditions necessary for viral RNA release. The proton-translocating FoF1 ATPase (ATP synthase) uses a proton gradient to drive adenosine triphosphate (ATP) synthesis. We have directly measured proton uptake in vesicles containing reconstituted M2 or FO by monitoring external pH after addition of valinomycin to vesicles with 100-fold diluted external [K+]. This proton flux assay was utilized to quantify proton flux through single M2 and Fo channels. Contrary to previous reports, proton uptake by M2 was not significantly altered by acidification of the extravesicular pH. We conclude that pH only weakly affects proton flux through M2 in the pH range of 5.4 - 7.0. Theoretical analysis utilized for such vesicle uptake assays illuminates the appropriate time scale of the initial slope and an important limitation that must be placed on inferences about channel ion selectivity. The rise in pH over 10 seconds after ionophore addition yielded time-averaged single channel conductances of 0.35±0.2 aS and 0.72±0.4 aS at pH 5.4 and 7.0 respectively. Such a low time-average conductance implies that M2 is only conductive 10^-6 to 10^-4 of the time. M2 selectivity for hydrogen over potassium is ~10^7. Fo translocates protons across membranes, converting electrochemical energy to rotational inertia. Previous experiments have been partially confounded by a contaminating channel, CL, which co-purifies with Fo and leaks cations. CL activity is shown to not decrease following deletion of the previously uncharacterized yraM open reading frame of E. coli. Fo purified from a deletion strain lacking yraM is just as active as Fo purified from the wild-type strain. Using Fo from the deletion strain, the single-hit hypothesis of DCCD inhibition of passive proton flux through Fo was examined. A DCCD-induced reduction in ATP synthase activity correlates with a reduction in the total initial slope, the number of functional Fo per µg protein, and the single channel proton flux. At least 2 DCCD per Fo are required to totally inactivate passive proton flux. M2 and Fo have similar single channel conductances but different open probabilities.

APA, Harvard, Vancouver, ISO, and other styles

10

Yücek, Tevfik. "Self-interference Handling in OFDM Based Wireless Communication Systems." Scholar Commons, 2003. https://scholarcommons.usf.edu/etd/1511.

Full text

Abstract:

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation scheme that provides efficient bandwidth utilization and robustness against time dispersive channels. This thesis deals with self-interference, or the corruption of desired signal by itself, in OFDM systems. Inter-symbol Interference (ISI) and Inter-carrier Interference (ICI) are two types of self-interference in OFDM systems. Cyclic prefix is one method to prevent the ISI which is the interference of the echoes of a transmitted signal with the original transmitted signal. The length of cyclic prefix required to remove ISI depends on the channel conditions, and usually it is chosen according to the worst case channel scenario. Methods to find the required parameters to adapt the length of the cyclic prefix to the instantaneous channel conditions are investigated. Frequency selectivity of the channel is extracted from the instantaneous channel frequency estimates and methods to estimate related parameters, e.g. coherence bandwidth and Root-mean-squared (RMS) delay spread, are given. These parameters can also be used to better utilize the available resources in wireless systems through transmitter and receiver adaptation. Another common self-interference in OFDM systems is the ICI which is the power leakage among different sub-carriers that degrades the performance of both symbol detection and channel estimation. Two new methods are proposed to reduce the effect of ICI in symbol detection and in channel estimation. The first method uses the colored nature of ICI to cancel it in order to decrease the error rate in the detection of transmitted symbols, and the second method reduces the effect of ICI in channel estimation by jointly estimating the channel and frequency offset, a major source of ICI.

APA, Harvard, Vancouver, ISO, and other styles

11

Macri, Vincenzo S. "The unique pore and selectivity filter of HCN channels." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/26833.

Full text

Abstract:

Hyperpolarization-activated Cyclic Nucleotide-modulated (HCN) channels are similar in structure and function to potassium channels. In both, changes in membrane voltage produce directionally similar movement of positively charged residues in the voltage sensor to alter the pore structure at the intracellular side and gate ion flow. Both classes of channels also allow mainly potassium ions to flow, are blocked by cesium ions, and are activated by extracellular potassium. However, HCN channels open when hyperpolarized, whereas most potassium channels open when depolarized. Thus, electromechanical coupling between the voltage sensor and gate is opposite. A key determinant of this coupling is the intrinsic stability of the pore. In potassium channels, the closed, and not the open, pore is more stable, however this it not known for HCN channels. HCN channels are also significantly permeable to sodium despite containing the GYG potassium channel signature selectivity filter sequence. In potassium channels, the selectivity filter sequence is ‘T/S-V/I/L/T-GYG’, which forms a row of four binding sites through which dehydrated potassium ions flow. In HCN channels, the equivalent residues are ‘C-I-GYG’, but whether they form four similarly arrayed cation binding sites is not known. In this thesis, we show using the mammalian HCN2 channel, that the stabilities of the open and closed pore are similar, the voltage sensor must apply force to close the pore, and that the interactions between the pore and voltage-sensor are weak. Furthermore, our data suggest that the conserved cysteine of the selectivity filter does not form a fourth binding site for permeating ions, which prevents it from contributing to either permeation or associated gating functions of the selectivity filter.

APA, Harvard, Vancouver, ISO, and other styles

12

Blockley, Alix Dawn. "Investigating the molecular basis of resistance and pyrethroid selectivity at acarine sodium channels." Thesis, Birkbeck (University of London), 2017. http://bbktheses.da.ulcc.ac.uk/252/.

Full text

Abstract:

Many acarine (tick and mite) species are ectoparasites of humans, livestock and domestic pets, where they spread disease and impact adversely on health. They are normally controlled through the application of acaricides; however, the prolonged use of individual compounds has resulted in many species developing resistance to specific pesticides. This thesis describes investigations into the molecular properties that determine the resistance to and selectivity of pyrethroids, an important class of pesticides that act on the voltage-gated sodium channels (VGSCs) of arthropod neurons. Comparison of insect and acarine VGSC sequences, coupled with molecular modelling studies, have identified a residue at amino-acid position 933 (M. domestica numbering) found within a putative pyrethroid binding pocket that may contribute to a greater selectivity of pyrethroids with comparatively larger halogenated groups for acarine VGSCs compared to those of insects. This is due to the presence of a smaller glycine residue at position 933 in acarine channels, compared to a cysteine residue in insect channels, which may enhance the binding of such pyrethroids (O'Reilly et al., 2014). This model is supported by the findings of Jonsson et al 2010, that R. microplus cattle ticks carrying the amino acid substitution G933V, are resistant to the pyrethroid flumethrin, which has a comparatively larger halogenated group, but not the pyrethroid cypermethrin, which has a comparatively smaller halogenated group. Work in this thesis describes progress made in the investigation of such specificity; involving sequencing studies, two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes involving insect and acarine VGSCs, and whole arthropod bioassays. While this work cannot conclusively disprove the model proposed by O’Reilly et al 2014, it suggests that the mechanisms of selectivity for pyrethroids in arthropods may involve the interplay of several factors, rather than being solely based upon structural variations in their VGSCs.

APA, Harvard, Vancouver, ISO, and other styles

13

Gibby, William Alexander Thomas. "Statistical theory of selectivity and conductivity in narrow biological ion channels : studies of KcsA." Thesis, Lancaster University, 2018. http://eprints.lancs.ac.uk/124053/.

Full text

Abstract:

Biological ion channels are essential for maintaining life, and appear as a seemingly paradoxical combination of both large conductivity and strong selection between ionic species. This process involves many complicated interactions, and their inclusion in a multi-species conduction model remains a fundamental theoretical challenge. In this thesis, we derive the theory of multi-species ionic conduction through narrow biological channels, taking into account ion-ion, ion-water and ion-channel interactions. The theories we derive lead to new results that describe multi-species conduction in and far from equilibrium in KcsA, including the resolution of the conductivity-selectivity paradox. The thesis builds on existing research on the physiological properties and structures of biological ion channels in deriving a first-principles, multi-species statistical and kinetic theory. The development of the statistical theory includes the derivation of the free energy, distribution and partition functions, as well as the statistical properties within the grand canonical ensemble. The conductivity of the channels is also derived using linear response theory and the generalised Einstein relation. The development of the kinetic theory involves the analysis of the transition rates, and the calculation of current and selectivity ratios. The kinetic model is then validated by comparing the theoretical currents with the currents measured experimentally for the Shaker and KcsA potassium channels in five different external data sets. The main results of this thesis are: a derivation of the grand canonical ensemble for narrow channels with multiple binding sites and mixed-species bulk solutions; a derivation of the linear response theory of multi-species conduction in such channels; development of non-equilibrium multi-species kinetic equations, that describe the conductivity; the validation of the kinetic theory through comparison with experimental data sets; and the joint application of these derived theories to the multi-species conduction of KcsA in and far from equilibrium, which demonstrates the resolution of the conductivity-selectivity paradox. These results should be applicable to other narrow voltage-gated ion channels, and can describe multi-species conduction of neutral particles through zeolites.

APA, Harvard, Vancouver, ISO, and other styles

14

Lindberg, Diana. "Exploring Selectivity and Hysteresis : Kinetic Studies on a Potato Epoxide Hydrolase." Doctoral thesis, Uppsala universitet, Institutionen för biokemi och organisk kemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-112285.

Full text

Abstract:

The kinetic mechanism of an α/β hydrolase fold epoxide hydrolase from potato, StEH1, has been studied with the aims of explaining the underlying causes for enantio- and regioselectivity, both being important for product purity. Further effort has been laid upon understanding the causes of a hysteretic behavior discovered in the measurements leading to Paper I. The enantioselectivity was investigated with substrates differing only in substituent size at one carbon of the oxirane ring structure. In catalysis with trans-stilbene oxide and styrene oxide, enantioselectivity is the result of differences in alkylation rates. In pre-steady state measurement with trans-2-methylstyrene oxide (2-MeSO), a rate-limiting step involving slow transitions, referred to as hysteresis, was discovered. With this substrate enantioselectivity is proposed to be a consequence of the catalytic rate of (1R,2R)-enantiomer being more influenced by the hysteretic behavior than was the rate of the other enantiomer. In steady-state measurements with (1R,2R)-2-MeSO, at different temperatures and pH, hysteretic cooperativity was displayed. It can be concluded that this behavior is dependent on the relationship between kcat and the rate of transition between two Michaelis complexes. From the differences in pH dependence of kcat/KM in formation of the two diols resulting from low regioselectivity in catalysis of (1R,2R)-2-MeSO, it is suggested that hysteresis is a result of the substrates placed in different conformational modes within the active site cavity. Regioselectivity is proposed to be the result of specific interactions between the catalytically important Tyr and the substrate, with a link between KM-values and degree of regioselectivity. Furthermore, the hysteretic kinetic model proposed can explain hysteresis, cooperativity and regioselectivity resulting from StEH1 catalyzed hydrolysis of (1R,2R)-2-MeSO.

APA, Harvard, Vancouver, ISO, and other styles

15

Reincke, Momsen [Verfasser]. "Inactivation and anion selectivity of volume-regulated anion channels depend on C-terminal residues of the first extracellular loop / Momsen Reincke." Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2017. http://d-nb.info/1140486772/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Gleissner, Filip. "Koexistence mobilních komunikačních systémů GSM-EDGE a UMTS." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233470.

Full text

Abstract:

The dissertation thesis deals with the investigation of the coexistence of GSM–EDGE and UMTS systems with focus on the physical layer of the systems. The aim is to provide a set of recommendations for practical cooperation while the systems operate in both the separated and the common radio bands. A detailed description of signal processing of both the systems on the physical layer is presented. On the basis of this description, models of both systems were created and implemented in the MATLAB environment. The simulations are focused on the physical layer quality parameters, especially the bit error ratio evaluation for various ratios of useful signal power to noise power during the transmission over the radio channel. Simulation is also used to examine the quality of received useful signal while it is interfered by signals from the same and adjacent channels. The purpose is to determine the isolation between these adjacent channels, when the bit error ratio of the useful signal does not exceed a certain reference value. The simulation results are subsequently subjected to comparison with the results of the experimental measurements in laboratory conditions. Before the measurements are carried out, a study of possible interference types is performed. Consequently, the crucial parameters of the measuring equipment used are verified. From the results of simulations and measurements, the proposal of a minimum and recommended carrier separation between both the systems is presented in order to efficiently utilize the assigned frequency spectrum. Furthermore, for the cooperation in both the separated and the common radio bands, the necessary precautions are given for reaching the required isolation and thereby inter-system interference minimization.

APA, Harvard, Vancouver, ISO, and other styles

17

Vierock, Johannes Tobias Theodor. "Molekularer Mechanismus protonenleitender Kanalrhodopsine und protonengekoppelte Zwei-Komponenten-Optogenetik." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21617.

Full text

Abstract:

Kanalrhodopsine (ChRs) sind lichtaktivierte Ionenkanäle motiler Algen. Heterolog exprimiert erlauben sie es, Ionenflüsse durch Licht zu steuern. Bevorzugt geleitet werden von den meisten ChRs Protonen. Ausprägung und Wirkung lichtaktivierter Protonenflüsse sowie der molekulare Mechanismus protonenselektiver ChRs werden in vorliegender Arbeit untersucht und zur Entwicklung neuer optogenetischer Werkzeuge genutzt. Eine besonders hohe Protonenselektivität zeigten die grün- und rotlicht-aktivierten Kanäle CsChR und Chrimson aus den Algen Chloromonas subdivisa und Chlamydomonas noctigama. Im spektroskopisch detailliert untersuchten CrChR2 aus Chlamydomonas reinhardtii änderte sich die Protonenselektivität nach Anregung mit einem ns-Laserblitz sogar innerhalb eines Aktivierungszyklus und war insbesondere nach Öffnung des Kanals sowie in Folge der Lichtadaptation hoch. Als unentbehrlich für eine effiziente Protonenleitung erwiesen sich in allen drei Kanälen konservierte, titrierbare Reste entlang der Pore, deren individuelle Bedeutung für die Protonenleitung sich je nach Protein wesentlich unterschied. Entsprechend genügte in Chrimson der Austausch einzelner Glutaminsäuren des extrazellulären Halbkanals, dieses in einen grün- oder rotlichtaktivierten Natriumkanal zu transformieren. Aminosäuresubstitutionen der unmittelbaren Retinalumgebung verschoben hingegen das Aktionsmaximum von Chrimson röter als 600 nm und damit röter als in allen bisher beschriebenen ChRs. In Chrimson versperrt hierbei ein zusätzliches äußeres Tor den extrazellulär Halbkanal, während die Retinalbindetasche in Struktur und funktionaler Bedeutung der einzelnen Reste wesentlich jener der Protonenpumpe Bacteriorhodopsin ähnelt. Als Zwei-Komponenten-Optogenetik wurden schließlich protonen-, kationen- und anionenleitende ChRs unterschiedlicher Farbsensitivität fusioniert sowie lichtgetriebene Protonenpumpen mit protonenaktivierten Ionenkanälen kombiniert und neue optogenetische Perspektiven eröffnet.
Channelrhodopsins (ChRs) are light-gated ion channels from green algae. Expressed in host cells they are used to control ion fluxes by light and are widely applied in Neurosciences. Although generally classified as either cation or anion channels, most ChRs preferentially conduct protons. This thesis compares proton conductance of different ChRs, examines the molecular mechanism of proton selective ChRs and explores the usage of light regulated proton fluxes in two-component-optogenetics. Proton selectivity varied strongly among different ChRs and was most pronounced for the green- and red-light activated channels CsChR and Chrimson from the algae Chloromonas subdivisa and Chlamydomonas noctigama, that conducted predominantly protons even at high pH. In CrChR2 from Chlamydomonas reinhardtii proton selectivity also changed during a single activation cycle and was especially high directly after channel opening and later on following light adaptation. In all three channels efficient proton conductance depended on conserved titratable residues along the pore with different contribution of the individual side chains in each protein. The substitution of single glutamic acids in the extracellular half pore converted Chrimson into a green or red-light activated sodium channel. A single point mutation close to the retinal chromophore shifted peak absorption of Chrimson beyond 600 nm - further red than all other cation conducting ChRs. Whereas the retinal binding pocket of Chrimson resembles the proton pump Bacteriorhodpsin, the overall pore structure corresponds to other ChRs, but features an additional outer gate, that occludes the extracellular half pore and is important for both, proton selectivity and red light absorption. Finally different Two-Component-Optogenetic approaches combined proton and anion selective ChRs of distinct colour as well as light-driven proton pumps and proton-activated ion channels with major prospect for future optogenetic applications.

APA, Harvard, Vancouver, ISO, and other styles

18

Capistrano, Maria de F?tima Pessoa. "Papel da localiza??o da carga em determina??o dos par?metros do canal i?nico." Universidade Federal do Rio Grande do Norte, 2007. http://repositorio.ufrn.br:8080/jspui/handle/123456789/13124.

Full text

Abstract:

Made available in DSpace on 2014-12-17T14:13:23Z (GMT). No. of bitstreams: 1 MariaFPC.pdf: 4835234 bytes, checksum: 942393c30ace33adf0d4efd21ae5bc99 (MD5) Previous issue date: 2007-11-05
To aureus α-HL channel, we used the cysteine-scanning mutagenesis technique. Twenty-four mutants were produced from the substitution of a single aminoacid of the primary structure of the α-HL pro this yzed after the incorporation of a mutant channel in planar lipid bilayer membranes. The modified proteins were studied in the absence and presence of watersoluble specific sulphydryl-specific reagents, in order to introduce a strong positive or negative harge at positions of substitution. The introduction of a negative charge in the stem region onverted the selectivity of the channel from weak anionic to more cationic. However, the troduction of a positive charge increased its selectivity to the anion. The degree of these alterations was inversely dependent on the channel radius at the position of the introduced harge (selectivity). As to the asymmetry of the conductance-voltage, the influence of the harge was more complex. The introduction of the negative charge in the stem region (the trans art of the pore) provoked a decrease. The intensity of these alterations depended on the radius, and on the type of free charge at the pore entrance. These results suggest that the free charge at surrounds the pore wall is responsible for the cation-anion selectivity of the channel. The istribution of the charges between the entrances is crucial for determining the asymmetry of e conductance-voltage curves. We hope that these results serve as a model for studies with other nanometric channels, in biological or planar lipid bilayer membranes or in iotechnological applications
Para investigar as influ?ncias das cargas sobre as propriedades do canal formado pela α-HL do Staphylococcus aureus, foi empregada a t?cnica de Escaneamento Mutagenese da Ciste?na . Vinte e quatro mutantes foram produzidos a partir da substitui??o de um ?nico amino?cido da estrutura prim?ria da prote?na α-HL pela ciste?na, em v?rias posi??es. As altera??es eletrofisiol?gicas, em decorr?ncia dessa modifica??o, foram analisadas, ap?s a incorpora??o do canal mutante em bicamada lip?dica plana. As prote?nas modificadas foram investigadas na aus?ncia e na presen?a de reagentes espec?ficos para sulfidrila, visando introduzir uma forte carga positiva ou negativa na posi??o da substitui??o. A introdu??o de uma carga negativa, na regi?o troncular (parte trans do poro) do canal formado pela α-HL, converteu a seletividade do canal de pouco ani?nico para mais cati?nico, entretanto a introdu??o de uma carga positiva aumentou, sua seletividade ao anion. A intensidade dessas altera??es foi inversamente dependente do raio do poro na posi??o da carga introduzida. Quanto ao par?metro assimetria da depend?ncia da condut?ncia-voltagem, a influ?ncia da carga foi mais complexa: a incorpora??o de uma carga negativa na regi?o troncular induziu aumento da assimetria, j? a incorpora??o ? regi?o copal (parte cis do poro) provocou uma diminui??o. A intensidade destas altera??es dependeu do raio, do tipo da carga m?vel introduzida sobre o eixo longitudinal do canal, sendo maior nas posi??es das cargas pr?xima das entradas do poro. Esses resultados sugerem que a carga livre que reveste a parede do lume do poro seja respons?vel pela seletividade c?tion-anion do canal. Considerando que a distribui??o das cargas entre as entradas seja fundamental, para determinar a assimetria da curva de depend?ncia condut?ncia-voltagem. N?s esperamos que esses resultados sirvam de modelo para estudos com outros canais de dimens?es nanom?tricas, em membranas biol?gicas ou bicamadas lip?dicas planas e para aplica??es biotecnol?gicas

APA, Harvard, Vancouver, ISO, and other styles

19

Schreiber, Susanne. "Frequency preference and reliability of signal integration." Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972577084.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Kun-ChengLin and 林坤正. "Channel Selectivity Mitigated Complementary CodedMIMO-CDMA Systems." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/82396671144527012485.

Full text

Abstract:

碩士
國立成功大學
工程科學系碩博士班
101
Perfect orthogonality is always an important feature for complementary code. The system based on this feature can use both time domain and frequency domain to resist interference. In the past proofs of [1] and [7], equal gains assumption is used to prove the perfect orthogonality of complementary code but in the practical transmission, signal will face different channel gains, and it will break the orthogonality of code. In this thesis, we prove the orthogonality of complete complementary code under different channel gains and propose a new system to deal with it. By using the feature of complete complementary code, this system can estimate channel gains and use the information of channel to compensate signal, the usage of code’s orthogonality will be optimal and the system’s performance will be enhanced as well.

APA, Harvard, Vancouver, ISO, and other styles

21

Cordero-Morales, Julio F. "Molecular determinants of gating at the potassium channel selectivity filter." 2008. http://proquest.umi.com/pqdweb?did=1801444121&sid=3&Fmt=2&clientId=3507&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Ahrari, Sajjad. "Structural dynamics of the selectivity filter in HCN1 ion channel." Thesis, 2020. http://hdl.handle.net/1866/24514.

Full text

Abstract:

Les canaux HCN (cycliques nucléotidiques) activés par hyperpolarisation appartiennent à la superfamille des canaux cationiques voltage-dépendants et sont responsables de la génération de courant drôle (If) dans les cellules cardiaques et neuronales. Malgré la similitude structurelle globale avec le potassium voltage-dépendant (Kv) et les canaux ioniques cycliques nucléotidiques (CNG), ils montrent un modèle de sélectivité distinctif pour les ions K+ et Na+. Plus précisément, leur perméabilité accrue aux ions Na+ est essentielle à son rôle dans la dépolarisation des membranes cellulaires. Ils sont également l'une des seules protéines connues à sélectionner entre les ions Na+ et Li+, faisant des HCN des canaux semi-sélectifs. Ici, nous étudions les propriétés de sélectivité uniques des canaux HCN à l'aide de simulations de dynamique moléculaire. Nos simulations suggèrent que le pore HCN1 est très flexible et dilaté par rapport aux canaux Kv et qu'il n'y a qu'un seul site de liaison ionique stable dans le filtre de sélectivité qui les distingue des canaux Kv et CNG. Nous observons également que la coordination et l'hydratation des ions diffèrent dans le filtre de sélectivité de HCN1 par rapport aux canaux Kv et CNG. De plus, la coordination des ions K+ par les groupes carbonyle du filtre de sélectivité est plus stable par rapport aux ions Na+ et Li+, ce qui peut expliquer les propriétés de sélectivité distinctes du canal.
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels belong to the voltage-gated cation channel superfamily and are responsible for the generation of funny current (If) in cardiac and neuronal cells. Despite the overall structural similarity to voltage-gated potassium (Kv) and cyclic nucleotide-gated (CNG) ion channels, they show distinctive selectivity pattern for K+ and Na+ ions. Specifically, their increased permeability to Na+ ions is critical to its role in depolarizing cellular membranes. They are also one of the only known proteins to select between Na+ and Li+ ions, making HCNs semi-selective channels. Here we investigate the unique selectivity properties of HCN channels using molecular dynamics simulations. Our simulations suggest that the HCN1 pore is very flexible and dilatated compared to Kv channels and that there is only one stable ion binding site within the selectivity filter which discriminates them from both Kv and CNG channels. We also observe that ion co-ordination and hydration differ within the selectivity filter of HCN1 compared to Kv and CNG channels. Additionally, the co-ordination of K+ ions by the carbonyl groups of the selectivity filter is more stable compared to Na+ and Li+ ions, which may explain the channel's distinct selectivity properties.

APA, Harvard, Vancouver, ISO, and other styles

23

Pessoa, João Pedro Abreu. "Cyclic nucleotide regulation in a potassium channel: ligand selectivity and conformational change." Tese, 2014. https://repositorio-aberto.up.pt/handle/10216/80883.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Pessoa, João Pedro Abreu. "Cyclic nucleotide regulation in a potassium channel: ligand selectivity and conformational change." Doctoral thesis, 2014. https://repositorio-aberto.up.pt/handle/10216/80883.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Lindy, Amanda Sue. "Functional Analysis of Ion Selectivity and Permeation Mechanisms of the C. elegans TRPV Channel OSM-9." Diss., 2011. http://hdl.handle.net/10161/5643.

Full text

Abstract:

For all organisms, the ability to sense and react to noxious environments is fundamental to their survival. For multi-celled organisms this process generally involves a nervous system and an extensive network of signal transduction pathways. TRPV ion channels have been shown to participate in signal transduction in response to noxious stimuli. At the cellular level these channels function in sensing of mechanical, thermal, and osmotic stimuli, and at the organismal level they function in homeostasis and nociception. TRPV ion channels participate in nociceptive signal transduction via cation influx, but exactly how these channels function at a mechanistic level and lead to activation of the cell or induction of a specific behavior is elusive. Previous research has shown that the pore-forming unit of an ion channel is critical for channel regulation, gating, ion selectivity, and ion permeation. Various regulatory domains have been identified to date in the pore-forming unit of TRP channels and a clearer picture of channel gating is beginning to emerge, but less is known about ion permeation.

To better understand the specific domains that are critical to ion capture, selectivity, and permeation in TRPV channels, we investigated the function of these regions using the C. elegans TRPV channel OSM-9 in vivo, and the mammalian TRPV channel TRPV4 in heterologous cell culture. OSM-9 is the functional ortholog of mammalian TRPV4 and it is likely that critical domains identified in OSM-9 are functionally conserved in TRPV4 and play a similar role in other TRPV channels. OSM-9 is expressed in the ASH neurons and is responsible for all of the behaviors initiated by that cell. The stereotypical avoidance behavior mediated by ASH, in response to noxious stimuli, serves as a model for nociception in vertebrates. As OSM-9 is necessary for all of these behavioral responses, activation of ASH acts as a read-out for OSM-9 function.

Through targeted mutagenesis of the OSM-9 loop domains and transgenic expression directed to the ASH head sensory neurons in an osm-9 null background, we discovered a critical role for the amino acids both N- and C- terminal to the pore helix in osmotic avoidance behavior. We confirmed the existence of a selectivity filter C-terminal to the pore helix and revealed that the turret is critical for channel function, possibly as a component of the inactivation gate.

We first identified the boundaries of the selectivity filter to be M601-F609. We also determined what properties of those residues were critical to Ca2+ and Na+ selectivity. In vivo Ca2+ imaging strongly suggested that residues Y604, D605, and F609 are critical for Ca2+ entry into the cell. Patch-clamp electrophysiology of a chimeric ion channel consisting largely of rat TRPV4, but encompassing transmembranes 5 through 6 of OSM-9, revealed that OSM-9 conducts both Ca2+ and Na+. Mutation Y604G disrupted both Ca2+ and Na+ conductance, whereas mutations Y604F and Y606A increased or maintained Na+ conductance and severely reduced Ca2+ conductance, while maintaining avoidance behavior. Homology modeling of OSM-9, based on an alignment of OSM-9 to Kv1.2, suggests that Y604 and F609 serve structural roles in maintaining filter constraints. Thus, aromatic and negative residues in the OSM-9 selectivity filter are critical to ion permeation and selectivity.

Our studies involving the selectivity filter support previous research that the selectivity filter is critical for TRP channel function. We also provide evidence that the selectivity filter is critical for nocifensive animal behavior. Fewer studies, however, have investigated the TM5-pore helix linker, known as the turret. The turret is believed to function in the binding of ligands and toxins in K+ channels, and more recently was suggested to be critical for temperature sensing in TRPV1. We investigated the function of the turret residues in several sensory submodalities of the OSM-9 channel and found that all deletions tested result in channel defects, including gain- and loss-of-function phenotypes. Several charge reversal mutations in the OSM-9 turret also resulted in partial defects. The discovery of a gain-of-function mutation indicates that the turret functions in gating. When the turret is mutated in this way, the channel is unable to enter into the inactivated state, allowing continued ion influx after repeated stimulation. The loss-of-function phenotypes indicate that the secondary structure of the turret is critical to the function of the channel, and perhaps gating. These findings, combined with the observed charge-reversal defects, support the conclusion that the turret is necessary for transducing conformational changes in response to stimuli.

Our in vivo findings on the external pore forming structures increase the understanding of ion permeation in TRP channels and clarify mechanisms of activation in nociceptor neurons in vivo. Furthermore, these studies enhance our insights into evolution of mammalian nociception in view of the established functional orthology of OSM-9 and TRPV4.

Dissertation

APA, Harvard, Vancouver, ISO, and other styles

26

Guan, Wendy. "Domain II (S5-P) region in Lymnaea T-type calcium channels and its role in determining biophysical properties, ion selectivity and drug sensitivity." Thesis, 2014. http://hdl.handle.net/10012/8507.

Full text

Abstract:

Invertebrate T-type calcium channels cloned from the great pond snail, Lymnaea Stagnalis (LCav3) possess highly sodium permeant ion channel currents by means of alternative splicing of exon 12. Exon 12 is located on the extracellular turret and the descending helix between segments 5 and segments 6, upstream of the ion selectivity filter in Domain II. Highly-sodium permeant T-type channels are generated without altering the selectivity filter locus, the primary regulatory domain known to govern ion selectivity for calcium and sodium channels. Comparisons of exon 12 sequences between invertebrates and vertebrate T-type channels reveals a conserved pattern of cysteine residues. Calcium-selective mammalian T-type channels possess a single cysteine in exon 12 in comparison to invertebrate T-type channels with either a tri- or penta- cysteine framework. Cysteine residues in exon 12 were substituted with a neutral amino acid, alanine in LCav3 channels harbouring exon 12a and 12b to mimic the turret structure of vertebrate T-type channels. The results generated T-type channels that were even more sodium-permeable than the native T-type channels in snails. Furthermore, permeant divalent ions similar in structure to calcium (eg. barium) were unable to sufficiently block the monovalent ion current of channels lacking cysteines in Domain II, suggesting that the pore is highly sodium permeant, and has weak affinity and block by permeant divalent ions other than calcium. Besides ion selectivity, the cysteine mutated T-type channels were 10 to 100 fold more sensitive to inhibition by nickel and zinc, respectively. The cysteine mutation data highly suggests that the cysteines form an extracellular structure that regulates ion selectivity and shields T-type channels from block by nickel and zinc. In addition, we replaced exon 12 from the sodium permeant snail T-type channel with exon 12 from human Cav3.2 channels. The snail T-type channel with exon 12 from human T-type channels produced a T-type channel that was modestly sodium permeable, but did not confer the high calcium permeability of Cav3.2 channels. These findings suggest that the cysteine containing extracellular domains in exon 12 are not sufficient to generate calcium selective channels similar to human Cav3.2 and likely work in concert with other extracellular domains to regulate the calcium or sodium selectivity of T-type channels.

APA, Harvard, Vancouver, ISO, and other styles

27

Sanders, Rachel Sarah. "Aminocyclodextrin ion channels : development of a model for ligand gating and investigations of the effects of channel structure on transport properties and ion selectivity /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3223711.

Full text

Abstract:

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006.
Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3809. Adviser: Mary S. Gin. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

APA, Harvard, Vancouver, ISO, and other styles

28

Madhavan, Nandita. "An anion selective aminocyclodextrin ion channel : ion selectivity, pH sensitivity and potential as a scaffold for light gating /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3223662.

Full text

Abstract:

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006.
Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3804. Adviser: Mary S. Gin. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

APA, Harvard, Vancouver, ISO, and other styles

29

Schmidt, Emily Grace. "Synthesis and study of biomimetic ion channels : (1) toward the development of a cyclic peptide-based redox-gated channel, and (2) investigations into the effect of pore size on the ion selectivity of an aminocyclodextrin channel /." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3270020.

Full text

Abstract:

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2007.
Source: Dissertation Abstracts International, Volume: 68-06, Section: B, page: 3796. Adviser: Mary S. Gin. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

APA, Harvard, Vancouver, ISO, and other styles

30

Senatore, Adriano. "Alternative splicing of Lymnaea Cav3 and NALCN ion channel genes serves to alter biophysical properties, membrane expression, and ion selectivity." Thesis, 2012. http://hdl.handle.net/10012/6926.

Full text

Abstract:

Evidence is presented that Lymnaea contains homologues for mammalian Cav3 and NALCN 4-domain ion channels, which retain key amino acid sequence motifs that differentiate these channels from other 4-domain types. Molecular cloning and heterologous expression of the first invertebrate Cav3 channel cDNA from Lymnaea confirms that it indeed is a true homologue to mammalian Cav3 channels, retaining some hallmark biophysical and pharmacological features1. Interestingly, the Lymnaea Cav3 channel gene also exhibits alternative splicing that is conserved with mammalian Cav3.1 and Cav3.2 channels, with homologous exons 8b in the I-II linker (Cav3.1) and 25c in the III-IV linker (Cav3.1 and Cav3.2), that can selectively be included or omitted from the full length channel. We show that the developmental and spatial expression patterns of these splice variants are remarkably conserved, and that these splice variants produce analogous changes in membrane localization and biophysical properties when channels are expressed in HEK-293T cells. The Lymnaea Cav3 channel gene also undergoes alternative splicing in the domain II P-loop, with mutually exclusive exons 12A and 12B that code for a large portion of the P-loop just upstream of the selectivity filter. Such splicing is a novel discovery that is not conserved with vertebrates or any other deuterostome animal, all of which only contain 12A homologues of exon 12. However, protostome animals including Lymnaea stagnalis, Drosophila melanogaster, and C. elegans all have mutually exclusive 12A and 12B exons in their Cav3 channel genes. Evidence is presented that exon 12A is likely the ancestral exon for the domain II P-loop, and that alternate exon 12B evolved later. Furthermore, although the two Lymnaea variants possess the same selectivity filter motifs characteristic for Cav3 channels (i.e. EEDD), they exhibit dramatic differences in calcium vs. sodium selectivity, without significant differences in biophysical properties. This is the first account of alternative splicing used to modulate ion selectivity in a Cav3 channel homologue, and given that calcium is such an important electrogenic signaling molecule, these alterations are expected to have profound physiological implications. Amazingly, Lymnaea NALCN was also found to undergo alternative splicing in the domain II P-loop, but in this case, the entire P-loop is replaced by mutually exclusive exons 15a and 15b such that the selectivity filter is converted from the proposed non-selective sodium-permeable configuration (15b/EKEE; EEKE in mammals, nematodes and insects), to a calcium channel-like pore (15a/EEEE). Thorough phylogenetic analysis reveals that NALCN is extremely unconventional, in that alternative splicing has frequently and independently evolved to alter the selectivity filter in domains II or III, in multiple animal clades. Furthermore, the ancestral NALCN channel most likely contained an EEEE pore. This work brings into question NALCN???s proposed role as a major leak sodium conductance that depolarizes neurons to help set the resting membrane potential, since some species possess only an EEEE variant, and based on homology to other 4-domain ion channels, this should render the channel calcium-selective. Unfortunately, heterologous expression and electrophysiological characterization of the two Lymnaea NALCN isoforms was unsuccessful, corroborating with others the inability to record NALCN ionic currents in heterologous systems.

APA, Harvard, Vancouver, ISO, and other styles

31

Nayak, Tapan Kumar. "Biophysical Studies On The Plastic And Cooperative Properties Of Single Voltage Gated Na+ And Leak K+ Ion Channels." Thesis, 2009. http://hdl.handle.net/2005/1090.

Full text

Abstract:

Ion channels are fundamental molecules in the nervous system that catalyze the flux of ions across the cell membrane. There are mounting evidences suggesting that the kinetic properties of ion channels undergo activity-dependent changes in various pathophysiological conditions. Here such activity-dependent changes were studied in case of two different ion channels; the rat brain derived voltage-gated Na+ channel, rNav1.2 and the human background leak K+ channel, hTREK1 using the single channel patch-clamp technique. Our results on the voltage-gated Na+ channel (Chapter III) illustrated that sustained membrane depolarization, as seen in pathophysiological conditions like epilepsy, induced a defined non-linear variation in the unitary conductance, activation, inactivation and recovery kinetic properties of the channel. Signal processing tools attributed a pseudo-oscillatory nature to the non-linearity observed in the channel properties. Prolonged membrane depolarization also induced a “molecular memory” phenomenon, characterized by clustering of dwell time events and strong autocorrelation in the dwell time series. The persistence of such molecular memory was found to be dependent on the duration of depolarization. Similar plastic changes were observed in case of the hTREK1 channel in presence of saturating concentrations of agonist, trichloroethanol (TCE) (Chapter IV). TREK1 channel behaves similar to single enzyme molecules with a single binding site for the substrate K+ ion whereas TCE acts as an allosteric activator of the channel. We observed that with increasing concentration of TCE (10 M to 10 mM) the catalytic turnover rate exhibited progressive departure from monoexponential to multi-exponential distribution suggesting the presence of ‘dynamic disorder’ analogous to single enzyme molecules. In addition, we observed the induction of strong correlation in successive waiting times and flux intensities, exemplified by distinct mode switching between high and low flux activity, which implied the induction of memory in single ion channel. Our observation of such molecular memory in two different ion channels in different experimental conditions highlights the importance and generality of the phenomenon which is normally hidden under the ensemble behaviour of ion channels. In the final part of the work (chapter V) we observed strong negative cooperativity and half-of-sites saturation kinetics in the interaction of local anesthetic, lidocaine with hTREK1 channel. We also mapped the specific anesthetic binding site in the c-terminal domain of the channel. Further, single channel analysis and the heterodimer studies enabled us to propose a model for this interaction and provide a plausible paradigm for the inhibitory action of lidocaine on hTREK1.

APA, Harvard, Vancouver, ISO, and other styles

32

Hub, Jochen Sebastian. "Selectivity, Regulation, and Inhibition of Aquaporin Channels. A Molecular Dynamics Study." Doctoral thesis, 2008. http://hdl.handle.net/11858/00-1735-0000-000D-F11B-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Forenza, Antonio. "Antenna and algorithm design in MIMO communication systems: exploiting the spatial selectivity of wireless channels." Thesis, 2006. http://hdl.handle.net/2152/2457.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Hub, Jochen Sebastian [Verfasser]. "Selectivity, regulation, and inhibition of aquaporin channels : a molecular dynamics study / vorgelegt von Jochen Sebastian Hub." 2008. http://d-nb.info/989090450/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Pudi, Thabo Israel. "Teacher attitudes towards the implementation of the learning area technology." Thesis, 2002. http://hdl.handle.net/10500/835.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Channel selectivity'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles