scholarly journals Intrinsic Mechanisms in the Gating of Resurgent Na+ Currents

2021 ◽  
Author(s):  
Joseph L. Ransdell ◽  
Jonathan D. Moreno ◽  
Druv Bhagavan ◽  
Jonathan R. Silva ◽  
Jeanne M. Nerbonne
Keyword(s):  
Voltage Clamp ◽  
Sodium Current ◽  
Neuronal Cell ◽  
Purkinje Neurons ◽  
Relative Distribution ◽  
Membrane Hyperpolarization ◽  
Voltage Gated ◽  
Nav Channels ◽  
Cerebellar Purkinje Neurons ◽  
Kinetics Of

ABSTRACTThe resurgent component of the voltage-gated sodium current (INaR) is a depolarizing conductance, revealed on membrane hyperpolarizations following brief depolarizing voltage steps, which has been shown to contribute to regulating the firing properties of numerous neuronal cell types throughout the central and peripheral nervous systems. Although mediated by the same voltage-gated sodium (Nav) channels that underlie the transient and persistent Nav current components, the gating mechanisms that contribute to the generation of INaR remain unclear. Here, we characterized Nav currents in mouse cerebellar Purkinje neurons, and used tailored voltage-clamp protocols to define how the voltage and the duration of the initial membrane depolarization affect the amplitudes and kinetics of INaR. Using the acquired voltage-clamp data, we developed a novel Markov kinetic state model with parallel (fast and slow) inactivation pathways and, we show that this model reproduces the properties of the resurgent, as well as the transient and persistent, Nav currents recorded in (mouse) cerebellar Purkinje neurons. Based on the acquired experimental data and the simulations, we propose that resurgent Na+ influx occurs as a result of fast inactivating Nav channels transitioning into an open/conducting state on membrane hyperpolarization, and that the decay of INaR reflects the slow accumulation of recovered/opened Nav channels into a second, alternative and more slowly populated, inactivated state. Additional simulations reveal that extrinsic factors that affect the kinetics of fast or slow Nav channel inactivation and/or impact the relative distribution of Nav channels in the fast- and slow-inactivated states, such as the accessory Navβ4 channel subunit, can modulate the amplitude of INaR.SUMMARYThe resurgent component of the voltage-gated sodium current (INaR) is revealed on membrane hyperpolarizations following brief depolarizing voltage steps that activate the rapidly activating and inactivating, transient Nav current (INaT). To probe the mechanisms contributing to the generation and properties of INaR, we combined whole-cell voltage-clamp recordings from mouse cerebellar Purkinje neurons with computational modeling to develop a novel, blocking particle-independent, model for the gating of INaR that involves two parallel inactivation pathways, and we show that this model recapitulates the detailed biophysical properties of INaR measured in mouse cerebellar Purkinje neurons.

scholarly journals Calmodulin limits pathogenic Na+ channel persistent current

2017 ◽  
Vol 149 (2) ◽  
pp. 277-293 ◽  
Author(s):  
Haidun Yan ◽  
Chaojian Wang ◽  
Steven O. Marx ◽  
Geoffrey S. Pitt
Keyword(s):  
Cardiac Arrhythmias ◽  
Persistent Current ◽  
Purkinje Neurons ◽  
Na Channel ◽  
Wild Type ◽  
Na Current ◽  
Voltage Gated ◽  
Nav Channels ◽  
Cerebellar Purkinje Neurons ◽  
Terminal Domains

Increased “persistent” current, caused by delayed inactivation, through voltage-gated Na+ (NaV) channels leads to cardiac arrhythmias or epilepsy. The underlying molecular contributors to these inactivation defects are poorly understood. Here, we show that calmodulin (CaM) binding to multiple sites within NaV channel intracellular C-terminal domains (CTDs) limits persistent Na+ current and accelerates inactivation across the NaV family. Arrhythmia or epilepsy mutations located in NaV1.5 or NaV1.2 channel CTDs, respectively, reduce CaM binding either directly or by interfering with CTD–CTD interchannel interactions. Boosting the availability of CaM, thus shifting its binding equilibrium, restores wild-type (WT)–like inactivation in mutant NaV1.5 and NaV1.2 channels and likewise diminishes the comparatively large persistent Na+ current through WT NaV1.6, whose CTD displays relatively low CaM affinity. In cerebellar Purkinje neurons, in which NaV1.6 promotes a large physiological persistent Na+ current, increased CaM diminishes the persistent Na+ current, suggesting that the endogenous, comparatively weak affinity of NaV1.6 for apoCaM is important for physiological persistent current.

scholarly journals Pharmacologically Targeting the Fibroblast Growth Factor 14 Interaction Site on the Voltage-Gated Na+ Channel 1.6 Enables Isoform-Selective Modulation

2021 ◽  
Vol 22 (24) ◽  
pp. 13541
Author(s):  
Nolan M. Dvorak ◽  
Cynthia M. Tapia ◽  
Aditya K. Singh ◽  
Timothy J. Baumgartner ◽  
Pingyuan Wang ◽  
...  
Keyword(s):  
Growth Factor ◽  
Action Potential ◽  
Fibroblast Growth Factor ◽  
Neuronal Cell ◽  
Fibroblast Growth ◽  
Α Subunit ◽  
Interaction Site ◽  
Voltage Gated ◽  
Selective Modulation ◽  
Nav Channels

Voltage-gated Na+ (Nav) channels are the primary molecular determinant of the action potential. Among the nine isoforms of the Nav channel α subunit that have been described (Nav1.1-Nav1.9), Nav1.1, Nav1.2, and Nav1.6 are the primary isoforms expressed in the central nervous system (CNS). Crucially, these three CNS Nav channel isoforms display differential expression across neuronal cell types and diverge with respect to their subcellular distributions. Considering these differences in terms of their localization, the CNS Nav channel isoforms could represent promising targets for the development of targeted neuromodulators. However, current therapeutics that target Nav channels lack selectivity, which results in deleterious side effects due to modulation of off-target Nav channel isoforms. Among the structural components of the Nav channel α subunit that could be pharmacologically targeted to achieve isoform selectivity, the C-terminal domains (CTD) of Nav channels represent promising candidates on account of displaying appreciable amino acid sequence divergence that enables functionally unique protein–protein interactions (PPIs) with Nav channel auxiliary proteins. In medium spiny neurons (MSNs) of the nucleus accumbens (NAc), a critical brain region of the mesocorticolimbic circuit, the PPI between the CTD of the Nav1.6 channel and its auxiliary protein fibroblast growth factor 14 (FGF14) is central to the generation of electrical outputs, underscoring its potential value as a site for targeted neuromodulation. Focusing on this PPI, we previously developed a peptidomimetic derived from residues of FGF14 that have an interaction site on the CTD of the Nav1.6 channel. In this work, we show that whereas the compound displays dose-dependent effects on the activity of Nav1.6 channels in heterologous cells, the compound does not affect Nav1.1 or Nav1.2 channels at comparable concentrations. In addition, we show that the compound correspondingly modulates the action potential discharge and the transient Na+ of MSNs of the NAc. Overall, these results demonstrate that pharmacologically targeting the FGF14 interaction site on the CTD of the Nav1.6 channel is a strategy to achieve isoform-selective modulation, and, more broadly, that sites on the CTDs of Nav channels interacted with by auxiliary proteins could represent candidates for the development of targeted therapeutics.

scholarly journals Effects of Sesamin, the Major Furofuran Lignan of Sesame Oil, on the Amplitude and Gating of Voltage-Gated Na+ and K+ Currents

Molecules ◽  
2020 ◽  
Vol 25 (13) ◽  
pp. 3062 ◽  
Author(s):  
Ping-Chung Kuo ◽  
Zi-Han Kao ◽  
Shih-Wei Lee ◽  
Sheng-Nan Wu
Keyword(s):  
Ionic Currents ◽  
Sesame Oil ◽  
Delayed Rectifier ◽  
Excitable Cells ◽  
Voltage Gated ◽  
Ic50 Value ◽  
Different Types ◽  
Nav Channels ◽  
Kinetics Of ◽  
K Currents

Sesamin (SSM) and sesamolin (SesA) are the two major furofuran lignans of sesame oil and they have been previously noticed to exert various biological actions. However, their modulatory actions on different types of ionic currents in electrically excitable cells remain largely unresolved. The present experiments were undertaken to explore the possible perturbations of SSM and SesA on different types of ionic currents, e.g., voltage-gated Na+ currents (INa), erg-mediated K+ currents (IK(erg)), M-type K+ currents (IK(M)), delayed-rectifier K+ currents (IK(DR)) and hyperpolarization-activated cation currents (Ih) identified from pituitary tumor (GH3) cells. The exposure to SSM or SesA depressed the transient and late components of INa with different potencies. The IC50 value of SSM needed to lessen the peak or sustained INa was calculated to be 7.2 or 0.6 μM, while that of SesA was 9.8 or 2.5 μM, respectively. The dissociation constant of SSM-perturbed inhibition on INa, based on the first-order reaction scheme, was measured to be 0.93 μM, a value very similar to the IC50 for its depressant action on sustained INa. The addition of SSM was also effective at suppressing the amplitude of resurgent INa. The addition of SSM could concentration-dependently inhibit the IK(M) amplitude with an IC50 value of 4.8 μM. SSM at a concentration of 30 μM could suppress the amplitude of IK(erg), while at 10 μM, it mildly decreased the IK(DR) amplitude. However, the addition of neither SSM (10 μM) nor SesA (10 μM) altered the amplitude or kinetics of Ih in response to long-lasting hyperpolarization. Additionally, in this study, a modified Markovian model designed for SCN8A-encoded (or NaV1.6) channels was implemented to evaluate the plausible modifications of SSM on the gating kinetics of NaV channels. The model demonstrated herein was well suited to predict that the SSM-mediated decrease in peak INa, followed by increased current inactivation, which could largely account for its favorable decrease in the probability of the open-blocked over open state of NaV channels. Collectively, our study provides evidence that highlights the notion that SSM or SesA could block multiple ion currents, such as INa and IK(M), and suggests that these actions are potentially important and may participate in the functional activities of various electrically excitable cells in vivo.

scholarly journals FGF14 modulates resurgent sodium current in mouse cerebellar Purkinje neurons

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Haidun Yan ◽  
Juan L Pablo ◽  
Chaojian Wang ◽  
Geoffrey S Pitt
Keyword(s):  
Sodium Current ◽  
Direct Interaction ◽  
Purkinje Neurons ◽  
Repetitive Firing ◽  
Spinocerebellar Ataxias ◽  
Channel Inactivation ◽  
C Terminus ◽  
N Terminus ◽  
Resurgent Current ◽  
Cerebellar Purkinje Neurons

Rapid firing of cerebellar Purkinje neurons is facilitated in part by a voltage-gated Na+ (NaV) ‘resurgent’ current, which allows renewed Na+ influx during membrane repolarization. Resurgent current results from unbinding of a blocking particle that competes with normal channel inactivation. The underlying molecular components contributing to resurgent current have not been fully identified. In this study, we show that the NaV channel auxiliary subunit FGF14 ‘b’ isoform, a locus for inherited spinocerebellar ataxias, controls resurgent current and repetitive firing in Purkinje neurons. FGF14 knockdown biased NaV channels towards the inactivated state by decreasing channel availability, diminishing the ‘late’ NaV current, and accelerating channel inactivation rate, thereby reducing resurgent current and repetitive spiking. Critical for these effects was both the alternatively spliced FGF14b N-terminus and direct interaction between FGF14b and the NaV C-terminus. Together, these data suggest that the FGF14b N-terminus is a potent regulator of resurgent NaV current in cerebellar Purkinje neurons.

Differential roles of two types of voltage-gated Ca2+ channels in the dendrites of rat cerebellar Purkinje neurons

1998 ◽  
Vol 791 (1-2) ◽  
pp. 43-55 ◽  
Author(s):  
Shigeo Watanabe ◽  
Hiroshi Takagi ◽  
Tsugumichi Miyasho ◽  
Masashi Inoue ◽  
Yutaka Kirino ◽  
...  
Keyword(s):  
Purkinje Neurons ◽  
Voltage Gated ◽  
Cerebellar Purkinje Neurons ◽  
Ca2 Channels
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