scholarly journals Differential Effects of Modified Batrachotoxins on Voltage-gated Sodium Channel Fast and Slow Inactivation

2021 ◽  
Author(s):  
Tim M. G. MacKenzie ◽  
Fayal Abderemane-Ali ◽  
Catherine E. Garrison ◽  
Daniel L. Minor Jr. ◽  
Justin Du Bois
Keyword(s):  
De Novo ◽  
Protein Complexes ◽  
Transmembrane Protein ◽  
Ion Selectivity ◽  
Allosteric Modulators ◽  
Slow Inactivation ◽  
Voltage Gated ◽  
Functional Studies ◽  
Voltage Gated Sodium Channels ◽  
Initiation And Propagation

Voltage-gated sodium channels (Na<sub>V</sub>s), large transmembrane protein complexes responsible for the initiation and propagation of action potentials, are targets for a number of acute poisons. Many of these agents act as allosteric modulators of channel activity and serve as powerful chemical tools for understanding channel function. Batrachotoxin (BTX) is a steroidal amine derivative most commonly associated with poison dart frogs and is unique as a Na<sub>V</sub> ligand in that it alters every property of the channel, including threshold potential of activation, inactivation, ion selectivity, and ion conduction. Structure-function studies with BTX are limited, however, by the inability to access preparative quantities of this compound from natural sources. We have addressed this problem through <i>de novo</i> synthesis of BTX, which gives access to modified toxin structures. In this report, we detail electrophysiology studies of three BTX C20-ester derivatives against recombinant Na<sub>V</sub> subtypes (rat Na<sub>V</sub>1.4 and human Na<sub>V</sub>1.5). Two of these compounds, BTX-B and BTX-<sup>c</sup>Hx, are functionally equivalent to BTX, hyperpolarizing channel activation and blocking both fast and slow inactivation. BTX-yne—a C20-<i>n</i>-heptynoate ester—is a conspicuous outlier, eliminating fast but not slow inactivation. This unique property qualifies BTX-yne as the first reported Na<sub>V</sub> modulator that separates inactivation processes. These findings are supported by functional studies with bacterial Na<sub>V</sub>s (BacNa<sub>V</sub>s) that lack a fast inactivation gate. The availability of BTX-yne should advance future efforts aimed at understanding Na<sub>V</sub> gating mechanisms and designing allosteric regulators of Na<sub>V</sub> activity.

scholarly journals Differential Effects of Modified Batrachotoxins on Voltage-gated Sodium Channel Fast and Slow Inactivation

2021 ◽  
Author(s):  
Tim M. G. MacKenzie ◽  
Fayal Abderemane-Ali ◽  
Catherine E. Garrison ◽  
Daniel L. Minor Jr. ◽  
Justin Du Bois
Keyword(s):  
De Novo ◽  
Protein Complexes ◽  
Transmembrane Protein ◽  
Ion Selectivity ◽  
Allosteric Modulators ◽  
Slow Inactivation ◽  
Voltage Gated ◽  
Functional Studies ◽  
Voltage Gated Sodium Channels ◽  
Initiation And Propagation

Voltage-gated sodium channels (Na<sub>V</sub>s), large transmembrane protein complexes responsible for the initiation and propagation of action potentials, are targets for a number of acute poisons. Many of these agents act as allosteric modulators of channel activity and serve as powerful chemical tools for understanding channel function. Batrachotoxin (BTX) is a steroidal amine derivative most commonly associated with poison dart frogs and is unique as a Na<sub>V</sub> ligand in that it alters every property of the channel, including threshold potential of activation, inactivation, ion selectivity, and ion conduction. Structure-function studies with BTX are limited, however, by the inability to access preparative quantities of this compound from natural sources. We have addressed this problem through <i>de novo</i> synthesis of BTX, which gives access to modified toxin structures. In this report, we detail electrophysiology studies of three BTX C20-ester derivatives against recombinant Na<sub>V</sub> subtypes (rat Na<sub>V</sub>1.4 and human Na<sub>V</sub>1.5). Two of these compounds, BTX-B and BTX-<sup>c</sup>Hx, are functionally equivalent to BTX, hyperpolarizing channel activation and blocking both fast and slow inactivation. BTX-yne—a C20-<i>n</i>-heptynoate ester—is a conspicuous outlier, eliminating fast but not slow inactivation. This unique property qualifies BTX-yne as the first reported Na<sub>V</sub> modulator that separates inactivation processes. These findings are supported by functional studies with bacterial Na<sub>V</sub>s (BacNa<sub>V</sub>s) that lack a fast inactivation gate. The availability of BTX-yne should advance future efforts aimed at understanding Na<sub>V</sub> gating mechanisms and designing allosteric regulators of Na<sub>V</sub> activity.

scholarly journals Voltage Gated Sodium Channel Genes in Epilepsy: Mutations, Functional Studies, and Treatment Dimensions

2021 ◽  
Vol 12 ◽  
Author(s):  
Ibitayo Abigail Ademuwagun ◽  
Solomon Oladapo Rotimi ◽  
Steffen Syrbe ◽  
Yvonne Ukamaka Ajamma ◽  
Ezekiel Adebiyi
Keyword(s):  
Ion Channel ◽  
Sodium Channel ◽  
Sodium Channels ◽  
De Novo ◽  
Single Gene ◽  
Voltage Gated ◽  
Functional Studies ◽  
Voltage Gated Sodium Channels ◽  
Genomic Studies ◽  
The Brain

Genetic epilepsy occurs as a result of mutations in either a single gene or an interplay of different genes. These mutations have been detected in ion channel and non-ion channel genes. A noteworthy class of ion channel genes are the voltage gated sodium channels (VGSCs) that play key roles in the depolarization phase of action potentials in neurons. Of huge significance are SCN1A, SCN1B, SCN2A, SCN3A, and SCN8A genes that are highly expressed in the brain. Genomic studies have revealed inherited and de novo mutations in sodium channels that are linked to different forms of epilepsies. Due to the high frequency of sodium channel mutations in epilepsy, this review discusses the pathogenic mutations in the sodium channel genes that lead to epilepsy. In addition, it explores the functional studies on some known mutations and the clinical significance of VGSC mutations in the medical management of epilepsy. The understanding of these channel mutations may serve as a strong guide in making effective treatment decisions in patient management.

Voltage-gated sodium channels and pain-related disorders

2016 ◽  
Vol 130 (24) ◽  
pp. 2257-2265 ◽  
Author(s):  
Alexandros H. Kanellopoulos ◽  
Ayako Matsuyama
Keyword(s):  
Sodium Channels ◽  
Protein Complexes ◽  
Transmembrane Protein ◽  
Kinetic Properties ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Wide Range ◽  
Neuronal Types ◽  
Firing Properties

Voltage-gated sodium channels (VGSCs) are heteromeric transmembrane protein complexes. Nine homologous members, SCN1A–11A, make up the VGSC gene family. Sodium channel isoforms display a wide range of kinetic properties endowing different neuronal types with distinctly varied firing properties. Among the VGSCs isoforms, Nav1.7, Nav1.8 and Nav1.9 are preferentially expressed in the peripheral nervous system. These isoforms are known to be crucial in the conduction of nociceptive stimuli with mutations in these channels thought to be the underlying cause of a variety of heritable pain disorders. This review provides an overview of the current literature concerning the role of VGSCs in the generation of pain and heritable pain disorders.

scholarly journals A gating charge interaction required for late slow inactivation of the bacterial sodium channel NavAb

2013 ◽  
Vol 142 (3) ◽  
pp. 181-190 ◽  
Author(s):  
Tamer M. Gamal El-Din ◽  
Gilbert Q. Martinez ◽  
Jian Payandeh ◽  
Todd Scheuer ◽  
William A. Catterall
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Late Phase ◽  
Membrane Potentials ◽  
Charge Movement ◽  
Slow Inactivation ◽  
Functional Studies ◽  
Voltage Gated Sodium Channels ◽  
Gating Charge ◽  
Charge Interaction

Voltage-gated sodium channels undergo slow inactivation during repetitive depolarizations, which controls the frequency and duration of bursts of action potentials and prevents excitotoxic cell death. Although homotetrameric bacterial sodium channels lack the intracellular linker-connecting homologous domains III and IV that causes fast inactivation of eukaryotic sodium channels, they retain the molecular mechanism for slow inactivation. Here, we examine the functional properties and slow inactivation of the bacterial sodium channel NavAb expressed in insect cells under conditions used for structural studies. NavAb activates at very negative membrane potentials (V1/2 of approximately −98 mV), and it has both an early phase of slow inactivation that arises during single depolarizations and reverses rapidly, and a late use-dependent phase of slow inactivation that reverses very slowly. Mutation of Asn49 to Lys in the S2 segment in the extracellular negative cluster of the voltage sensor shifts the activation curve ∼75 mV to more positive potentials and abolishes the late phase of slow inactivation. The gating charge R3 interacts with Asn49 in the crystal structure of NavAb, and mutation of this residue to Cys causes a similar positive shift in the voltage dependence of activation and block of the late phase of slow inactivation as mutation N49K. Prolonged depolarizations that induce slow inactivation also cause hysteresis of gating charge movement, which results in a requirement for very negative membrane potentials to return gating charges to their resting state. Unexpectedly, the mutation N49K does not alter hysteresis of gating charge movement, even though it prevents the late phase of slow inactivation. Our results reveal an important molecular interaction between R3 in S4 and Asn49 in S2 that is crucial for voltage-dependent activation and for late slow inactivation of NavAb, and they introduce a NavAb mutant that enables detailed functional studies in parallel with structural analysis.

scholarly journals Fluorine-19 NMR and computational quantification of isoflurane binding to the voltage-gated sodium channel NaChBac

2016 ◽  
Vol 113 (48) ◽  
pp. 13762-13767 ◽  
Author(s):  
Monica N. Kinde ◽  
Vasyl Bondarenko ◽  
Daniele Granata ◽  
Weiming Bu ◽  
Kimberly C. Grasty ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Binding Sites ◽  
Ion Selectivity ◽  
Selectivity Filter ◽  
Inactivation Kinetics ◽  
Voltage Gated Sodium Channel ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Binding Data ◽  
Quantitative Analyses

Voltage-gated sodium channels (NaV) play an important role in general anesthesia. Electrophysiology measurements suggest that volatile anesthetics such as isoflurane inhibit NaVby stabilizing the inactivated state or altering the inactivation kinetics. Recent computational studies suggested the existence of multiple isoflurane binding sites in NaV, but experimental binding data are lacking. Here we use site-directed placement of19F probes in NMR experiments to quantify isoflurane binding to the bacterial voltage-gated sodium channel NaChBac.19F probes were introduced individually to S129 and L150 near the S4–S5 linker, L179 and S208 at the extracellular surface, T189 in the ion selectivity filter, and all phenylalanine residues. Quantitative analyses of19F NMR saturation transfer difference (STD) spectroscopy showed a strong interaction of isoflurane with S129, T189, and S208; relatively weakly with L150; and almost undetectable with L179 and phenylalanine residues. An orientation preference was observed for isoflurane bound to T189 and S208, but not to S129 and L150. We conclude that isoflurane inhibits NaChBac by two distinct mechanisms: (i) as a channel blocker at the base of the selectivity filter, and (ii) as a modulator to restrict the pivot motion at the S4–S5 linker and at a critical hinge that controls the gating and inactivation motion of S6.

scholarly journals Ionic selectivity and thermal adaptations within the voltage-gated sodium channel family of alkaliphilic Bacillus

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Paul G DeCaen ◽  
Yuka Takahashi ◽  
Terry A Krulwich ◽  
Masahiro Ito ◽  
David E Clapham
Keyword(s):  
Divalent Cations ◽  
Ion Selectivity ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Ph Homeostasis ◽  
Ionic Selectivity ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Nav Channels ◽  
Alkaliphilic Bacillus

Entry and extrusion of cations are essential processes in living cells. In alkaliphilic prokaryotes, high external pH activates voltage-gated sodium channels (Nav), which allows Na+ to enter and be used as substrate for cation/proton antiporters responsible for cytoplasmic pH homeostasis. Here, we describe a new member of the prokaryotic voltage-gated Na+ channel family (NsvBa; Non-selective voltage-gated, Bacillus alcalophilus) that is nonselective among Na+, Ca2+ and K+ ions. Mutations in NsvBa can convert the nonselective filter into one that discriminates for Na+ or divalent cations. Gain-of-function experiments demonstrate the portability of ion selectivity with filter mutations to other Bacillus Nav channels. Increasing pH and temperature shifts their activation threshold towards their native resting membrane potential. Furthermore, we find drugs that target Bacillus Nav channels also block the growth of the bacteria. This work identifies some of the adaptations to achieve ion discrimination and gating in Bacillus Nav channels.

Voltage-Gated Sodium Channel β1 Gene: An Overview

2021 ◽  
pp. 1-9
Author(s):  
Hisham Al-Ward ◽  
Chun-Yang Liu ◽  
Ning Liu ◽  
Fahmi Shaher ◽  
Murad Al-Nusaif ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Brugada Syndrome ◽  
Protein Complexes ◽  
Sodium Ion ◽  
Dravet Syndrome ◽  
Β Subunit ◽  
Voltage Gated ◽  
Physiological Processes ◽  
Voltage Gated Sodium Channels

<b><i>Background:</i></b> Voltage-gated sodium channels are protein complexes composed of 2 subunits, namely, pore-forming α- and regulatory β-subunits. A β-subunit consists of 5 proteins encoded by 4 genes (i.e., <i>SCN1B–SCN4B</i>). <b><i>Summary:</i></b> β<sub>1</sub>-Subunits regulate sodium ion channel functions, including gating properties, subcellular localization, and kinetics. <b><i>Key Message:</i></b> Sodium channel β<sub>1</sub>- and its variant β<sub>1B</sub>-subunits are encoded by <i>SCN1B</i>. These variants are associated with many human diseases, such as epilepsy, Brugada syndrome, Dravet syndrome, and cancers. On the basis of previous research, we aimed to provide an overview of the structure, expression, and involvement of <i>SCN1B</i> in physiological processes and focused on its role in diseases.

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