scholarly journals Enhanced excitability of cortical neurons in low-divalent solutions is primarily mediated by altered voltage-dependence of voltage-gated sodium channels

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Briana J Martiszus ◽  
Timur Tsintsadze ◽  
Wenhan Chang ◽  
Stephen M Smith
Keyword(s):  
Cortical Neurons ◽  
Voltage Dependence ◽  
Wild Type ◽  
Calcium Sensing Receptor ◽  
Action Potential Firing ◽  
Voltage Gated ◽  
Calcium Sensing ◽  
Neocortical Neurons ◽  
Voltage Gated Sodium Channels ◽  
Potential Firing

Increasing extracellular [Ca2+] ([Ca2+]o) strongly decreases intrinsic excitability in neurons but the mechanism is unclear. By one hypothesis, [Ca2+]o screens surface charge, reducing voltage-gated sodium channel (VGSC) activation and by another [Ca2+]o activates Calcium-sensing receptor (CaSR) closing the sodium-leak channel (NALCN). Here we report that neocortical neurons from CaSR-deficient (Casr-/-) mice had more negative resting potentials and did not fire spontaneously in reduced divalent-containing solution (T0.2) compared to wild-type (WT). However, after setting membrane potential to -70 mV, T0.2 application similarly depolarized and increased action potential firing in Casr-/- and WT neurons. Enhanced activation of VGSCs was the dominant contributor to the depolarization and increase in excitability by T0.2 and occurred due to hyperpolarizing shifts in VGSC window currents. CaSR deletion depolarized VGSC window currents but did not affect NALCN activation. Regulation of VGSC gating by external divalents is the key mechanism mediating divalent-dependent changes in neocortical neuron excitability.

scholarly journals Discovery of a heme-binding domain in a neuronal voltage-gated potassium channel

2020 ◽  
Vol 295 (38) ◽  
pp. 13277-13286
Author(s):  
Mark J. Burton ◽  
Joel Cresser-Brown ◽  
Morgan Thomas ◽  
Nicola Portolano ◽  
Jaswir Basran ◽  
...  
Keyword(s):  
Cortical Neurons ◽  
Normal Function ◽  
Pas Domain ◽  
Heme Binding ◽  
Channel Activity ◽  
Action Potential Firing ◽  
Voltage Gated ◽  
Conserved Domain ◽  
Potential Firing ◽  
Eag Channels

The EAG (ether-à-go-go) family of voltage-gated K+ channels are important regulators of neuronal and cardiac action potential firing (excitability) and have major roles in human diseases such as epilepsy, schizophrenia, cancer, and sudden cardiac death. A defining feature of EAG (Kv10–12) channels is a highly conserved domain on the N terminus, known as the eag domain, consisting of a Per–ARNT–Sim (PAS) domain capped by a short sequence containing an amphipathic helix (Cap domain). The PAS and Cap domains are both vital for the normal function of EAG channels. Using heme-affinity pulldown assays and proteomics of lysates from primary cortical neurons, we identified that an EAG channel, hERG3 (Kv11.3), binds to heme. In whole-cell electrophysiology experiments, we identified that heme inhibits hERG3 channel activity. In addition, we expressed the Cap and PAS domain of hERG3 in Escherichia coli and, using spectroscopy and kinetics, identified the PAS domain as the location for heme binding. The results identify heme as a regulator of hERG3 channel activity. These observations are discussed in the context of the emerging role for heme as a regulator of ion channel activity in cells.

Sensory renal innervation: a kidney-specific firing activity due to a unique expression pattern of voltage-gated sodium channels?

2013 ◽  
Vol 304 (5) ◽  
pp. F491-F497 ◽  
Author(s):  
Wolfgang Freisinger ◽  
Johannes Schatz ◽  
Tilmann Ditting ◽  
Angelika Lampert ◽  
Sonja Heinlein ◽  
...  
Keyword(s):  
Action Potential ◽  
Sodium Channels ◽  
Sensory Neurons ◽  
Firing Pattern ◽  
Drg Neurons ◽  
Action Potential Firing ◽  
Tonic Firing ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Potential Firing

Sensory neurons with afferent axons from the kidney are extraordinary in their response to electrical stimulation. More than 50% exhibit a tonic firing pattern, i.e., sustained action potential firing throughout depolarizing, pointing to an increased excitability, whereas nonrenal neurons show mainly a phasic response, i.e., less than five action potentials. Here we investigated whether these peculiar firing characteristics of renal afferent neurons are due to differences in the expression of voltage-gated sodium channels (Navs). Dorsal root ganglion (DRG) neurons from rats (Th11-L2) were recorded by the current-clamp technique and distinguished as “tonic” or “phasic.” In voltage-clamp recordings, Navs were characterized by their tetrodotoxoxin (TTX) sensitivity, and their molecular identity was revealed by RT-PCR. The firing pattern of 66 DRG neurons (41 renal and 25 nonrenal) was investigated. Renal neurons exhibited more often a tonic firing pattern (56.1 vs. 12%). Tonic neurons showed a more positive threshold (−21.75 ± 1.43 vs.−29.33 ± 1.63 mV; P < 0.05), a higher overshoot (56.74 [53.6–60.96] vs. 46.79 mV [38.63–54.75]; P < 0.05) and longer action potential duration (4.61 [4.15–5.85] vs. 3.35 ms [2.12–5.67]; P < 0.05). These findings point to an increased presence of the TTX-resistant Navs 1.8 and 1.9. Furthermore, tonic neurons exhibited a relatively higher portion of TTX-resistant sodium currents. Interestingly, mRNA expression of TTX-resistant sodium channels was significantly increased in renal, predominantly tonic, DRG neurons. Hence, under physiological conditions, renal sensory neurons exhibit predominantly a firing pattern associated with higher excitability. Our findings support that this is due to an increased expression and activation of TTX-resistant Navs.

Carisbamate, a novel neuromodulator, inhibits voltage-gated sodium channels and action potential firing of rat hippocampal neurons

2009 ◽  
Vol 83 (1) ◽  
pp. 66-72 ◽  
Author(s):  
Yi Liu ◽  
George J. Yohrling ◽  
Yan Wang ◽  
Tasha L. Hutchinson ◽  
Douglas E. Brenneman ◽  
...  
Keyword(s):  
Action Potential ◽  
Sodium Channels ◽  
Hippocampal Neurons ◽  
Action Potential Firing ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Potential Firing

scholarly journals CaSR modulates sodium channel-mediated Ca2+-dependent excitability

2021 ◽  
Author(s):  
Briana J. Martiszus ◽  
Timur Tsintsadze ◽  
Wenhan Chang ◽  
Stephen M. Smith
Keyword(s):  
Sodium Channel ◽  
Neuronal Excitability ◽  
Intrinsic Excitability ◽  
Null Mutant ◽  
Wild Type ◽  
Calcium Sensing Receptor ◽  
Leak Channel ◽  
Calcium Sensing ◽  
Neocortical Neurons ◽  
Voltage Dependent

AbstractIncreasing extracellular [Ca2+] ([Ca2+]o) strongly decreases intrinsic excitability in neurons but the mechanism is unclear. By one hypothesis, [Ca2+]o screens surface charge reducing voltage-dependent sodium channel (VGSC) activation and by another [Ca2+]o activates Calcium-sensing receptor (CaSR) closing the sodium-leak channel (NALCN). Here we report that action potential (AP) firing rates increased in wild-type (WT), but not CaSR null mutant (Casr-/-) neocortical neurons, following the switch from physiological to reduced Ca2+-containing Tyrode. However, after membrane potential correction, AP firing increased similarly in both genotypes inconsistent with CaSR regulation of NALCN. Activation of VGSCs was the dominant contributor to the increase in excitability after the [Ca2+]o change. VGSC conductance-voltage relationships were hyperpolarized by decreasing [Ca2+]o for Casr-/- neurons indicating CaSR contributes to [Ca2+]o-dependent excitability via VGSCs. Regulation of VGSC gating by [Ca2+]o is the key mechanism mediating [Ca2+]o-dependent changes in neocortical neuron excitability and CaSR influences neuronal excitability by its effects on VGSC gating.

scholarly journals AnkyrinG Is Required for Clustering of Voltage-gated Na Channels at Axon Initial Segments and for Normal Action Potential Firing

1998 ◽  
Vol 143 (5) ◽  
pp. 1295-1304 ◽  
Author(s):  
Daixing Zhou ◽  
Stephen Lambert ◽  
Peter L. Malen ◽  
Scott Carpenter ◽  
Linda M. Boland ◽  
...  
Keyword(s):  
Repetitive Firing ◽  
Action Potential Firing ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Progressive Ataxia ◽  
Skeletal Protein ◽  
Potential Firing ◽  
Subsequent Loss ◽  
Axon Initial Segments

Voltage-gated sodium channels (NaCh) are colocalized with isoforms of the membrane-skeletal protein ankyrinG at axon initial segments, nodes of Ranvier, and postsynaptic folds of the mammalian neuromuscular junction. The role of ankyrinG in directing NaCh localization to axon initial segments was evaluated by region-specific knockout of ankyrinG in the mouse cerebellum. Mutant mice exhibited a progressive ataxia beginning around postnatal day P16 and subsequent loss of Purkinje neurons. In mutant mouse cerebella, NaCh were absent from axon initial segments of granule cell neurons, and Purkinje cells showed deficiencies in their ability to initiate action potentials and support rapid, repetitive firing. Neurofascin, a member of the L1CAM family of ankyrin-binding cell adhesion molecules, also exhibited impaired localization to initial segments of Purkinje cell neurons. These results demonstrate that ankyrinG is essential for clustering NaCh and neurofascin at axon initial segments and is required for physiological levels of sodium channel activity.

scholarly journals pigkMutation underliesmachobehavior and affects Rohon-Beard cell excitability

2015 ◽  
Vol 114 (2) ◽  
pp. 1146-1157 ◽  
Author(s):  
V. Carmean ◽  
M. A. Yonkers ◽  
M. B. Tellez ◽  
J. R. Willer ◽  
G. B. Willer ◽  
...  
Keyword(s):  
Action Potential ◽  
Sensory Neurons ◽  
Sodium Current ◽  
Genetic Defect ◽  
Sensory Cells ◽  
Loss Of Function ◽  
Wild Type ◽  
Action Potential Firing ◽  
Potential Firing ◽  
Touch Response

The study of touch-evoked behavior allows investigation of both the cells and circuits that generate a response to tactile stimulation. We investigate a touch-insensitive zebrafish mutant, macho (maco), previously shown to have reduced sodium current amplitude and lack of action potential firing in sensory neurons. In the genomes of mutant but not wild-type embryos, we identify a mutation in the pigk gene. The encoded protein, PigK, functions in attachment of glycophosphatidylinositol anchors to precursor proteins. In wild-type embryos, pigk mRNA is present at times when mutant embryos display behavioral phenotypes. Consistent with the predicted loss of function induced by the mutation, knock-down of PigK phenocopies maco touch insensitivity and leads to reduced sodium current (INa) amplitudes in sensory neurons. We further test whether the genetic defect in pigk underlies the maco phenotype by overexpressing wild-type pigk in mutant embryos. We find that ubiquitous expression of wild-type pigk rescues the touch response in maco mutants. In addition, for maco mutants, expression of wild-type pigk restricted to sensory neurons rescues sodium current amplitudes and action potential firing in sensory neurons. However, expression of wild-type pigk limited to sensory cells of mutant embryos does not allow rescue of the behavioral touch response. Our results demonstrate an essential role for pigk in generation of the touch response beyond that required for maintenance of proper INa density and action potential firing in sensory neurons.

scholarly journals Calcium Signaling Regulates Trafficking of Familial Hypocalciuric Hypercalcemia (FHH) Mutants of the Calcium Sensing Receptor

2012 ◽  
Vol 26 (12) ◽  
pp. 2081-2091 ◽  
Author(s):  
Michael P. Grant ◽  
Ann Stepanchick ◽  
Gerda E. Breitwieser
Keyword(s):  
Plasma Membrane ◽  
Steady State ◽  
State Level ◽  
Membrane Targeting ◽  
Familial Hypocalciuric Hypercalcemia ◽  
Loss Of Function ◽  
Wild Type ◽  
Calcium Sensing Receptor ◽  
Dynamic Changes ◽  
Calcium Sensing

Abstract Calcium-sensing receptors (CaSRs) regulate systemic Ca2+ homeostasis. Loss-of-function mutations cause familial benign hypocalciuric hypercalcemia (FHH) or neonatal severe hyperparathyroidism (NSHPT). FHH/NSHPT mutations can reduce trafficking of CaSRs to the plasma membrane. CaSR signaling is potentiated by agonist-driven anterograde CaSR trafficking, leading to a new steady state level of plasma membrane CaSR, which is maintained, with minimal functional desensitization, as long as extracellular Ca2+ is elevated. This requirement for CaSR signaling to drive CaSR trafficking to the plasma membrane led us to reconsider the mechanism(s) contributing to dysregulated trafficking of FHH/NSHPT mutants. We simultaneously monitored dynamic changes in plasma membrane levels of CaSR and intracellular Ca2+, using a chimeric CaSR construct, which allowed explicit tracking of plasma membrane levels of mutant or wild-type CaSRs in the presence of nonchimeric partners. Expression of mutants alone revealed severe defects in plasma membrane targeting and Ca2+ signaling, which were substantially rescued by coexpression with wild-type CaSR. Biasing toward heterodimerization of wild-type and FHH/NSHPT mutants revealed that intracellular Ca2+ oscillations were insufficient to rescue plasma membrane targeting. Coexpression of the nonfunctional mutant E297K with the truncation CaSRΔ868 robustly rescued trafficking and Ca2+ signaling, whereas coexpression of distinct FHH/NSHPT mutants rescued neither trafficking nor signaling. Our study suggests that rescue of FHH/NSHPT mutants requires a steady state intracellular Ca2+ response when extracellular Ca2+ is elevated and argues that Ca2+ signaling by wild-type CaSRs rescues FHH mutant trafficking to the plasma membrane.

scholarly journals Tracking S4 movement by gating pore currents in the bacterial sodium channel NaChBac

2014 ◽  
Vol 144 (2) ◽  
pp. 147-157 ◽  
Author(s):  
Tamer M. Gamal El-Din ◽  
Todd Scheuer ◽  
William A. Catterall
Keyword(s):  
Membrane Potential ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Voltage Dependence ◽  
Periodic Paralysis ◽  
Membrane Potentials ◽  
Structural Basis ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Gating Charges

Voltage-gated sodium channels mediate the initiation and propagation of action potentials in excitable cells. Transmembrane segment S4 of voltage-gated sodium channels resides in a gating pore where it senses the membrane potential and controls channel gating. Substitution of individual S4 arginine gating charges (R1–R3) with smaller amino acids allows ionic currents to flow through the mutant gating pore, and these gating pore currents are pathogenic in some skeletal muscle periodic paralysis syndromes. The voltage dependence of gating pore currents provides information about the transmembrane position of the gating charges as S4 moves in response to membrane potential. Here we studied gating pore current in mutants of the homotetrameric bacterial sodium channel NaChBac in which individual arginine gating charges were replaced by cysteine. Gating pore current was observed for each mutant channel, but with different voltage-dependent properties. Mutating the first (R1C) or second (R2C) arginine to cysteine resulted in gating pore current at hyperpolarized membrane potentials, where the channels are in resting states, but not at depolarized potentials, where the channels are activated. Conversely, the R3C gating pore is closed at hyperpolarized membrane potentials and opens with channel activation. Negative conditioning pulses revealed time-dependent deactivation of the R3C gating pore at the most hyperpolarized potentials. Our results show sequential voltage dependence of activation of gating pore current from R1 to R3 and support stepwise outward movement of the substituted cysteines through the narrow portion of the gating pore that is sealed by the arginine side chains in the wild-type channel. This pattern of voltage dependence of gating pore current is consistent with a sliding movement of the S4 helix through the gating pore. Through comparison with high-resolution models of the voltage sensor of bacterial sodium channels, these results shed light on the structural basis for pathogenic gating pore currents in periodic paralysis syndromes.

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