scholarly journals Molecular Pathology of Sodium Channel Beta-Subunit Variants

2021 ◽  
Vol 12 ◽  
Author(s):  
Paweorn Angsutararux ◽  
Wandi Zhu ◽  
Taylor L. Voelker ◽  
Jonathan R. Silva
Keyword(s):  
Sodium Channel ◽  
Time Course ◽  
Macromolecular Complex ◽  
Excitable Cells ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Channel Expression ◽  
Familial Atrial Fibrillation ◽  
Voltage Sensing Domain ◽  
Pore Domain

The voltage-gated Na+ channel regulates the initiation and propagation of the action potential in excitable cells. The major cardiac isoform NaV1.5, encoded by SCN5A, comprises a monomer with four homologous repeats (I-IV) that each contain a voltage sensing domain (VSD) and pore domain. In native myocytes, NaV1.5 forms a macromolecular complex with NaVβ subunits and other regulatory proteins within the myocyte membrane to maintain normal cardiac function. Disturbance of the NaV complex may manifest as deadly cardiac arrhythmias. Although SCN5A has long been identified as a gene associated with familial atrial fibrillation (AF) and Brugada Syndrome (BrS), other genetic contributors remain poorly understood. Emerging evidence suggests that mutations in the non-covalently interacting NaVβ1 and NaVβ3 are linked to both AF and BrS. Here, we investigated the molecular pathologies of 8 variants in NaVβ1 and NaVβ3. Our results reveal that NaVβ1 and NaVβ3 variants contribute to AF and BrS disease phenotypes by modulating both NaV1.5 expression and gating properties. Most AF-linked variants in the NaVβ1 subunit do not alter the gating kinetics of the sodium channel, but rather modify the channel expression. In contrast, AF-related NaVβ3 variants directly affect channel gating, altering voltage-dependent activation and the time course of recovery from inactivation via the modulation of VSD activation.

The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Nav1.6 voltage-dependent sodium channel

2007 ◽  
Vol 293 (2) ◽  
pp. C783-C789 ◽  
Author(s):  
Christian Rosker ◽  
Birgit Lohberger ◽  
Doris Hofer ◽  
Bibiane Steinecker ◽  
Stefan Quasthoff ◽  
...  
Keyword(s):  
Steady State ◽  
Sodium Channels ◽  
Therapeutic Intervention ◽  
Time Course ◽  
Specific Interaction ◽  
Xenopus Laevis Oocytes ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Invaluable Tool

The blocking efficacy of 4,9-anhydro-TTX (4,9-ah-TTX) and TTX on several isoforms of voltage-dependent sodium channels, expressed in Xenopus laevis oocytes, was tested (Nav1.2, Nav1.3, Nav1.4, Nav1.5, Nav1.6, Nav1.7, and Nav1.8). Generally, TTX was 40–231 times more effective, when compared with 4,9-ah-TTX, on a given isoform. An exception was Nav1.6, where 4,9-ah-TTX in nanomole per liter concentrations sufficed to result in substantial block, indicating that 4,9-ah-TTX acts specifically at this peculiar isoform. The IC50 values for TTX/4,9-ah-TTX were as follows (in nmol/l): 7.8 ± 1.3/1,260 ± 121 (Nav1.2), 2.8 ± 2.3/341 ± 36 (Nav1.3), 4.5 ± 1.0/988 ± 62 (Nav1.4), 1,970 ± 565/78,500 ± 11,600 (Nav1.5), 3.8 ± 1.5/7.8 ± 2.3 (Nav1.6), 5.5 ± 1.4/1,270 ± 251 (Nav1.7), and 1,330 ± 459/>30,000 (Nav1.8). Analysis of approximal half-maximal doses of both compounds revealed minor effects on voltage-dependent activation only, whereas steady-state inactivation was shifted to more negative potentials by both TTX and 4,9-ah-TTX in the case of the Nav1.6 subunit, but not in the case of other TTX-sensitive ones. TTX shifted steady-state inactivation also to more negative potentials in case of the TTX-insensitive Nav1.5 subunit, where it also exerted profound effects on the time course of recovery from inactivation. Isoform-specific interaction of toxins with ion channels is frequently observed in the case of proteinaceous toxins. Although the sensitivity of Nav1.1 to 4,9-ah-TTX is not known, here we report evidence on a highly isoform-specific TTX analog that may well turn out to be an invaluable tool in research for the identification of Nav1.6-mediated function, but also for therapeutic intervention.

Regulation of Voltage-Dependent Sodium Channel Expression in Adrenal Chromaffin Cells

2002 ◽  
Vol 971 (1) ◽  
pp. 127-134 ◽  
Author(s):  
HIDEYUKI KOBAYASHI ◽  
SEIJI SHIRAISHI ◽  
TOSHIHIKO YANAGITA ◽  
HIROKI YOKOO ◽  
RYUICHI YAMAMOTO ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Chromaffin Cells ◽  
Adrenal Chromaffin Cells ◽  
Voltage Dependent ◽  
Channel Expression ◽  
Adrenal Chromaffin

scholarly journals A new mechanism of voltage-dependent gating exposed by KV10.1 channels interrupted between voltage sensor and pore

2017 ◽  
Vol 149 (5) ◽  
pp. 577-593 ◽  
Author(s):  
Adam P. Tomczak ◽  
Jorge Fernández-Trillo ◽  
Shashank Bharill ◽  
Ferenc Papp ◽  
Gyorgy Panyi ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Voltage Sensor ◽  
Ion Flow ◽  
Gating Model ◽  
Cryo Electron Microscopy ◽  
Channel Gate ◽  
Voltage Dependent ◽  
Voltage Gated Ion Channels ◽  
Voltage Sensing Domain ◽  
Pore Domain

Voltage-gated ion channels couple transmembrane potential changes to ion flow. Conformational changes in the voltage-sensing domain (VSD) of the channel are thought to be transmitted to the pore domain (PD) through an α-helical linker between them (S4–S5 linker). However, our recent work on channels disrupted in the S4–S5 linker has challenged this interpretation for the KCNH family. Furthermore, a recent single-particle cryo-electron microscopy structure of KV10.1 revealed that the S4–S5 linker is a short loop in this KCNH family member, confirming the need for an alternative gating model. Here we use “split” channels made by expression of VSD and PD as separate fragments to investigate the mechanism of gating in KV10.1. We find that disruption of the covalent connection within the S4 helix compromises the ability of channels to close at negative voltage, whereas disconnecting the S4–S5 linker from S5 slows down activation and deactivation kinetics. Surprisingly, voltage-clamp fluorometry and MTS accessibility assays show that the motion of the S4 voltage sensor is virtually unaffected when VSD and PD are not covalently bound. Finally, experiments using constitutively open PD mutants suggest that the presence of the VSD is structurally important for the conducting conformation of the pore. Collectively, our observations offer partial support to the gating model that assumes that an inward motion of the C-terminal S4 helix, rather than the S4–S5 linker, closes the channel gate, while also suggesting that control of the pore by the voltage sensor involves more than one mechanism.

scholarly journals Insights into the molecular mechanism for hyperpolarization-dependent activation of HCN channels

2018 ◽  
Vol 115 (34) ◽  
pp. E8086-E8095 ◽  
Author(s):  
Galen E. Flynn ◽  
William N. Zagotta
Keyword(s):  
Ion Channels ◽  
Cyclic Nucleotide ◽  
Electromechanical Coupling ◽  
Canonical Model ◽  
Hcn Channels ◽  
Voltage Gated ◽  
Kv Channels ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Pore Domain

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) ion channels are both voltage- and ligand-activated membrane proteins that contribute to electrical excitability and pace-making activity in cardiac and neuronal cells. These channels are members of the voltage-gated Kv channel superfamily and cyclic nucleotide-binding domain subfamily of ion channels. HCN channels have a unique feature that distinguishes them from other voltage-gated channels: the HCN channel pore opens in response to hyperpolarizing voltages instead of depolarizing voltages. In the canonical model of electromechanical coupling, based on Kv channels, a change in membrane voltage activates the voltage-sensing domains (VSD) and the activation energy passes to the pore domain (PD) through a covalent linker that connects the VSD to the PD. In this investigation, the covalent linkage between the VSD and PD, the S4-S5 linker, and nearby regions of spHCN channels were mutated to determine the functional role each plays in hyperpolarization-dependent activation. The results show that: (i) the S4-S5 linker is not required for hyperpolarization-dependent activation or ligand-dependent gating; (ii) the S4 C-terminal region (S4C-term) is not necessary for ligand-dependent gating but is required for hyperpolarization-dependent activation and acts like an autoinhibitory domain on the PD; (iii) the S5N-term region is involved in VSD–PD coupling and holding the pore closed; and (iv) spHCN channels have two voltage-dependent processes, a hyperpolarization-dependent activation and a depolarization-dependent recovery from inactivation. These results are inconsistent with the canonical model of VSD–PD coupling in Kv channels and elucidate the mechanism for hyperpolarization-dependent activation of HCN channels.

Slow inward Ca current in frog heart: theoretical evidence against a voltage-dependent inactivation

1982 ◽  
Vol 60 (9) ◽  
pp. 1185-1192 ◽  
Author(s):  
Rodolphe Fischmeister ◽  
Magda Horackova
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Frog Heart ◽  
Type Model ◽  
Actual Behavior ◽  
Ca Current ◽  
Recovery From Inactivation ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Theoretical Evidence

The validity of a Hodgkin–Huxley type voltage-dependent inactivation of slow inward Ca current (Isi) was tested in frog heart using a computer simulation. The time course of Isi, was calculated during the development of a frog atrial action potential (AP). With a time constant of inactivation (τf) of 55 ms at a membrane potential (Em) of –15 mV, the variation of Isi was biphasic; after a transient increase followed by a decrease to zero, Isi partially "reactivated" (at the beginning of the AP repolarization phase) and then fully deactivated. The "reactivation" phase of Isi developed whether τf was an increasing, decreasing, U-shaped, or bell-shaped function of Em. The addition of an independent and slower process responsible for the recovery from inactivation only partly suppressed the "reactivation" phase. However, until now there was no experimental evidence supporting such a biphasic variation of Isi during AP repolarization. Thus our results indicate that the Hodgkin–Huxley type model of the voltage-dependence of Isi-inactivation process may not correctly represent the actual behavior of frog cardiac muscle.

scholarly journals Augmentation of Recovery from Inactivation by Site-3 Na Channel Toxins

1999 ◽  
Vol 113 (2) ◽  
pp. 333-346 ◽  
Author(s):  
G. Richard Benzinger ◽  
Gayle S. Tonkovich ◽  
Dorothy A. Hanck
Keyword(s):  
Time Course ◽  
Genetic Diseases ◽  
Low Frequency ◽  
Periodic Paralysis ◽  
Na Channel ◽  
Na Channels ◽  
Cell Recovery ◽  
Reverse Transcription Pcr ◽  
Recovery From Inactivation ◽  
Voltage Dependent

Site-3 toxins isolated from several species of scorpion and sea anemone bind to voltage-gated Na channels and prolong the time course of INa by interfering with inactivation with little or no effect on activation, effects that have similarities to those produced by genetic diseases in skeletal muscle (myotonias and periodic paralysis) and heart (long QT syndrome). Some published reports have also reported the presence of a noninactivating persistent current in site-3 toxin-treated cells. We have used the high affinity site-3 toxin Anthopleurin B to study the kinetics of this current and to evaluate kinetic differences between cardiac (in RT4-B8 cells) and neuronal (in N1E-115 cells) Na channels. By reverse transcription–PCR from N1E-115 cell RNA multiple Na channel transcripts were detected; most often isolated were sequences homologous to rBrII, although at low frequency sequences homologous to rPN1 and rBrIII were also detected. Toxin treatment induced a voltage-dependent plateau current in both isoforms for which the relative amplitude (plateau current/peak current) approached a constant value with depolarization, although the magnitude was much greater for neuronal (17%) than cardiac (5%) INa. Cell-attached patch recordings revealed distinct quantitative differences in open times and burst durations between isoforms, but for both isoforms the plateau current comprised discrete bursts separated by quiescent periods, consistent with toxin induction of an increase in the rate of recovery from inactivation rather than a modal failure of inactivation. In accord with this hypothesis, toxin increased the rate of whole-cell recovery at all tested voltages. Moreover, experimental data support a model whereby recovery at negative voltages is augmented through closed states rather than through the open state. We conclude that site-3 toxins produce qualitatively similar effects in cardiac and neuronal channels and discuss implications for channel kinetics.

scholarly journals New Structures and Gating of Voltage-Dependent Potassium (Kv) Channels and Their Relatives: A Multi-Domain and Dynamic Question

2019 ◽  
Vol 20 (2) ◽  
pp. 248 ◽  
Author(s):  
Francisco Barros ◽  
Luis Pardo ◽  
Pedro Domínguez ◽  
Luisa Sierra ◽  
Pilar de la Peña
Keyword(s):  
General Structure ◽  
Cell Excitability ◽  
Kv Channels ◽  
Transmembrane Voltage ◽  
Voltage Dependent ◽  
Opening And Closing ◽  
Allosteric Mechanisms ◽  
Voltage Sensing Domain ◽  
Pore Domain

Voltage-dependent potassium channels (Kv channels) are crucial regulators of cell excitability that participate in a range of physiological and pathophysiological processes. These channels are molecular machines that display a mechanism (known as gating) for opening and closing a gate located in a pore domain (PD). In Kv channels, this mechanism is triggered and controlled by changes in the magnitude of the transmembrane voltage sensed by a voltage-sensing domain (VSD). In this review, we consider several aspects of the VSD–PD coupling in Kv channels, and in some relatives, that share a common general structure characterized by a single square-shaped ion conduction pore in the center, surrounded by four VSDs located at the periphery. We compile some recent advances in the knowledge of their architecture, based in cryo-electron microscopy (cryo-EM) data for high-resolution determination of their structure, plus some new functional data obtained with channel variants in which the covalent continuity between the VSD and PD modules has been interrupted. These advances and new data bring about some reconsiderations about the use of exclusively a classical electromechanical lever model of VSD–PD coupling by some Kv channels, and open a view of the Kv-type channels as allosteric machines in which gating may be dynamically influenced by some long-range interactional/allosteric mechanisms.

scholarly journals Voltage-dependent regulation of modal gating in the rat SkM1 sodium channel expressed in Xenopus oocytes.

1994 ◽  
Vol 104 (4) ◽  
pp. 625-643 ◽  
Author(s):  
S Ji ◽  
W Sun ◽  
A L George ◽  
R Horn ◽  
R L Barchi
Keyword(s):  
Sodium Channel ◽  
Xenopus Oocytes ◽  
Voltage Dependence ◽  
Alpha Subunit ◽  
Inactivation Kinetics ◽  
Voltage Range ◽  
Relative Contribution ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Two State Model

The TTX-sensitive rat skeletal muscle sodium channel (rSkM1) exhibits two modes of inactivation (fast vs slow) when the alpha subunit is expressed alone in Xenopus oocytes. In this study, two components are found in the voltage dependence of normalized current inactivation, one having a V1/2 in the expected voltage range (approximately -50 mV, I(N)) and the other with a more hyperpolarized V1/2 (approximately -130 mV, IH) at a holding potential of -90 mV. The I(N) component is associated with the gating mode having rapid inactivation and recovery from inactivation of the macroscopic current (N-mode), while IH corresponds to the slow inactivation and recovery mode (H-mode). These two components are interconvertible and their relative contribution to the total current varies with the holding potential: I(N) is favored by hyperpolarization. The interconversion between the two modes is voltage dependent and is well fit to a first-order two-state model with a voltage dependence of e-fold/8.6 mV and a V1/2 of -62 mV. When the rat sodium channel beta 1-subunit is coinjected with rSkM1, IH is essentially eliminated and the inactivation kinetics of macroscopic current becomes rapid. These two current components and their associated gating modes may represent two conformations of the alpha subunit, one of which can be stabilized either by hyperpolarization or by binding of the beta 1 subunit.

scholarly journals Voltage-Gated Sodium Channel Modulation by a New Spider Toxin Ssp1a Isolated From an Australian Theraphosid

2021 ◽  
Vol 12 ◽  
Author(s):  
Yashad Dongol ◽  
Phil M. Choi ◽  
David T. Wilson ◽  
Norelle L. Daly ◽  
Fernanda C. Cardoso ◽  
...  
Keyword(s):  
Rank Order ◽  
Structural Features ◽  
Docking Studies ◽  
Resonance Spectroscopy ◽  
Voltage Gated ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Dependent Inhibition ◽  
Voltage Sensing Domain ◽  
Subtype Selective

Given the important role of voltage-gated sodium (NaV) channel-modulating spider toxins in elucidating the function, pharmacology, and mechanism of action of therapeutically relevant NaV channels, we screened the venom from Australian theraphosid species against the human pain target hNaV1.7. Using assay-guided fractionation, we isolated a 33-residue inhibitor cystine knot (ICK) peptide (Ssp1a) belonging to the NaSpTx1 family. Recombinant Ssp1a (rSsp1a) inhibited neuronal hNaV subtypes with a rank order of potency hNaV1.7 > 1.6 > 1.2 > 1.3 > 1.1. rSsp1a inhibited hNaV1.7, hNaV1.2 and hNaV1.3 without significantly altering the voltage-dependence of activation, inactivation, or delay in recovery from inactivation. However, rSsp1a demonstrated voltage-dependent inhibition at hNaV1.7 and rSsp1a-bound hNaV1.7 opened at extreme depolarizations, suggesting rSsp1a likely interacted with voltage-sensing domain II (VSD II) of hNaV1.7 to trap the channel in its resting state. Nuclear magnetic resonance spectroscopy revealed key structural features of Ssp1a, including an amphipathic surface with hydrophobic and charged patches shown by docking studies to comprise the interacting surface. This study provides the basis for future structure-function studies to guide the development of subtype selective inhibitors.

Time- and voltage-dependent modulation of a Kv1.4 channel by a beta-subunit (Kv beta 3) cloned from ferret ventricle

1995 ◽  
Vol 269 (1) ◽  
pp. H385-H391 ◽  
Author(s):  
R. C. Castellino ◽  
M. J. Morales ◽  
H. C. Strauss ◽  
R. L. Rasmusson
Keyword(s):  
Time Course ◽  
Slow Component ◽  
Expression System ◽  
Beta Subunit ◽  
K Channel ◽  
Beta Subunits ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Current Activation ◽  
Oocyte Expression System

In mammals, voltage-gated K+ channels can be made of complexes containing alpha-subunits similar to the Shaker K+ channel and smaller cytoplasmic beta-subunits. Recent studies have suggested that these ancillary beta-subunits can modulate K+ channel gating properties. We studied the effects of a K+ channel beta-subunit, Kv beta 3, coexpressed with a Kv1.4 alpha-subunit, FK1, on the time and voltage dependence of channel activation, inactivation, recovery from inactivation, and deactivation, using an oocyte expression system. Kv beta 3 was found to accelerate both the fast and the slow component of Kv1.4 inactivation. Kv beta 3 also altered the relative contributions of the two components of inactivation by increasing the contribution of the slow component to the inactivation process. Kv beta 3 slowed recovery from inactivation for Kv1.4, but not for a Kv1.4 deletion mutant lacking N-type inactivation. Finally, steady-state activation and the time course of Kv1.4 current activation were not strongly influenced by Kv beta 3; however, deactivation was slowed in the presence of Kv beta 3. This study suggests that Kv beta 3 alters channel states which follow activation.

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