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Baeza-Loya S, Eatock RA. Effects of transient, persistent, and resurgent sodium currents on excitability and spike regularity in vestibular ganglion neurons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.11.28.569044. [PMID: 38076890 PMCID: PMC10705474 DOI: 10.1101/2023.11.28.569044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/20/2023]
Abstract
Vestibular afferent neurons occur as two populations with differences in spike timing regularity that are independent of rate. The more excitable regular afferents have lower current thresholds and sustained spiking responses to injected currents, while irregular afferent neurons have higher thresholds and transient responses. Differences in expression of low-voltage-activated potassium (K LV ) channels are emphasized in models of spiking regularity and excitability in these neurons, leaving open the potential contributions of the voltage-gated sodium (Na V ) channels responsible for the spike upstroke. We investigated the impact of different Na V current modes (transient, persistent, and resurgent) with whole-cell patch clamp experiments in mouse vestibular ganglion neurons (VGNs), the cultured and dissociated cell bodies of afferents. All VGNs had transient Na V current, many had a small persistent (non-inactivating) Na V current, and a few had resurgent current, which flows after the spike peak when Na V channels that were blocked are unblocked. Na V 1.6 channels conducted most or all of each Na V current mode, and a Na V 1.6-selective blocker decreased spike rate and altered spike waveforms in both sustained and transient VGNs. A Na V channel agonist enhanced persistent current and increased spike rate and regularity. We hypothesized that persistent and resurgent currents have different effects on sustained (regular) VGNs vs. transient (irregular) VGNs. Lacking blockers specific for the different current modes, we used modeling to isolate their effects on spiking of simulated transient and sustained VGNs, driven by simulated current steps and noisy trains of simulated EPSCs. In all simulated neurons, increasing transient Na V current increased spike rate and rate-independent regularity. In simulated sustained VGNs, adding persistent current increased both rate and rate-independent regularity, while adding resurgent current had limited impact. In transient VGNs, adding persistent current had little impact, while adding resurgent current increased both rate and rate-independent irregularity by enhancing sensitivity to synaptic noise. These experiments show that the small Na V current modes may enhance the differentiation of afferent populations, with persistent currents selectively making regular afferents more regular and resurgent currents selectively making irregular afferents less regular.
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2
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Brown SP, Lawson RJ, Moreno JD, Ransdell JL. A Reinterpretation of the Relationship between Persistent and Resurgent Sodium Currents. J Neurosci 2024; 44:e2396232024. [PMID: 38858080 PMCID: PMC11255426 DOI: 10.1523/jneurosci.2396-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 05/14/2024] [Accepted: 05/31/2024] [Indexed: 06/12/2024] Open
Abstract
The resurgent sodium current (INaR) activates on membrane repolarization, such as during the downstroke of neuronal action potentials. Due to its unique activation properties, INaR is thought to drive high rates of repetitive neuronal firing. However, INaR is often studied in combination with the persistent or noninactivating portion of sodium currents (INaP). We used dynamic clamp to test how INaR and INaP individually affect repetitive firing in adult cerebellar Purkinje neurons from male and female mice. We learned INaR does not scale repetitive firing rates due to its rapid decay at subthreshold voltages and that subthreshold INaP is critical in regulating neuronal firing rate. Adjustments to the voltage-gated sodium conductance model used in these studies revealed INaP and INaR can be inversely scaled by adjusting occupancy in the slow-inactivated kinetic state. Together with additional dynamic clamp experiments, these data suggest the regulation of sodium channel slow inactivation can fine-tune INaP and Purkinje neuron repetitive firing rates.
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Affiliation(s)
- Samuel P Brown
- Department of Biology, Miami University, Oxford, Ohio 45056
| | - Ryan J Lawson
- Department of Biology, Miami University, Oxford, Ohio 45056
| | - Jonathan D Moreno
- Division of Cardiology, Department of Medicine, Washington University in St. Louis, St. Louis, Missouri 63130
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3
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Aman TK, Raman IM. Resurgent current in context: Insights from the structure and function of Na and K channels. Biophys J 2024; 123:1924-1941. [PMID: 38130058 PMCID: PMC11309984 DOI: 10.1016/j.bpj.2023.12.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 12/07/2023] [Accepted: 12/18/2023] [Indexed: 12/23/2023] Open
Abstract
Discovered just over 25 years ago in cerebellar Purkinje neurons, resurgent Na current was originally described operationally as a component of voltage-gated Na current that flows upon repolarization from relatively depolarized potentials and speeds recovery from inactivation, increasing excitability. Its presence in many excitable cells and absence from others has raised questions regarding its biophysical and molecular mechanisms. Early studies proposed that Na channels capable of generating resurgent current are subject to a rapid open-channel block by an endogenous blocking protein, which binds upon depolarization and unblocks upon repolarization. Since the time that this mechanism was suggested, many physiological and structural studies of both Na and K channels have revealed aspects of gating and conformational states that provide insights into resurgent current. These include descriptions of domain movements for activation and inactivation, solution of cryo-EM structures with pore-blocking compounds, and identification of native blocking domains, proteins, and modulatory subunits. Such results not only allow the open-channel block hypothesis to be refined but also link it more clearly to research that preceded it. This review considers possible mechanisms for resurgent Na current in the context of earlier and later studies of ion channels and suggests a framework for future research.
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Affiliation(s)
- Teresa K Aman
- Department of Neurobiology, Northwestern University, Evanston, Illinois
| | - Indira M Raman
- Department of Neurobiology, Northwestern University, Evanston, Illinois.
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4
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Pozzi E, Terribile G, Cherchi L, Di Girolamo S, Sancini G, Alberti P. Ion Channel and Transporter Involvement in Chemotherapy-Induced Peripheral Neurotoxicity. Int J Mol Sci 2024; 25:6552. [PMID: 38928257 PMCID: PMC11203899 DOI: 10.3390/ijms25126552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2024] [Revised: 06/06/2024] [Accepted: 06/11/2024] [Indexed: 06/28/2024] Open
Abstract
The peripheral nervous system can encounter alterations due to exposure to some of the most commonly used anticancer drugs (platinum drugs, taxanes, vinca alkaloids, proteasome inhibitors, thalidomide), the so-called chemotherapy-induced peripheral neurotoxicity (CIPN). CIPN can be long-lasting or even permanent, and it is detrimental for the quality of life of cancer survivors, being associated with persistent disturbances such as sensory loss and neuropathic pain at limb extremities due to a mostly sensory axonal polyneuropathy/neuronopathy. In the state of the art, there is no efficacious preventive/curative treatment for this condition. Among the reasons for this unmet clinical and scientific need, there is an uncomplete knowledge of the pathogenetic mechanisms. Ion channels and transporters are pivotal elements in both the central and peripheral nervous system, and there is a growing body of literature suggesting that they might play a role in CIPN development. In this review, we first describe the biophysical properties of these targets and then report existing data for the involvement of ion channels and transporters in CIPN, thus paving the way for new approaches/druggable targets to cure and/or prevent CIPN.
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Affiliation(s)
- Eleonora Pozzi
- Experimental Neurology Unit, School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (E.P.); (L.C.); (S.D.G.)
| | - Giulia Terribile
- Human Physiology Unit, School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (G.T.); (G.S.)
| | - Laura Cherchi
- Experimental Neurology Unit, School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (E.P.); (L.C.); (S.D.G.)
| | - Sara Di Girolamo
- Experimental Neurology Unit, School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (E.P.); (L.C.); (S.D.G.)
| | - Giulio Sancini
- Human Physiology Unit, School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (G.T.); (G.S.)
| | - Paola Alberti
- Experimental Neurology Unit, School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (E.P.); (L.C.); (S.D.G.)
- Fondazione IRCCS San Gerardo dei Tintori, 20900 Monza, Italy
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5
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Brown SP, Lawson RJ, Moreno JD, Ransdell JL. A Reinterpretation of the Relationship Between Persistent and Resurgent Sodium Currents. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.10.25.564042. [PMID: 38187680 PMCID: PMC10769191 DOI: 10.1101/2023.10.25.564042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
The resurgent sodium current (INaR) activates on membrane repolarization, such as during the downstroke of neuronal action potentials. Due to its unique activation properties, INaR is thought to drive high rates of repetitive neuronal firing. However, INaR is often studied in combination with the persistent or non-inactivating portion of sodium currents (INaP). We used dynamic clamp to test how INaR and INaP individually affect repetitive firing in adult cerebellar Purkinje neurons from male and female mice. We learned INaR does not scale repetitive firing rates due to its rapid decay at subthreshold voltages, and that subthreshold INaP is critical in regulating neuronal firing rate. Adjustments to the Nav conductance model used in these studies revealed INaP and INaR can be inversely scaled by adjusting occupancy in the slow inactivated kinetic state. Together with additional dynamic clamp experiments, these data suggest the regulation of sodium channel slow inactivation can fine-tune INaP and Purkinje neuron repetitive firing rates.
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Affiliation(s)
| | - Ryan J. Lawson
- Department of Biology, Miami University, Oxford, OH 45056
| | - Jonathan D. Moreno
- Division of Cardiology, Department of Medicine, Washington University in St. Louis, St. Louis, MO 63130
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John SR, Phillips RS, Rubin JE. A novel mechanism for ramping bursts based on slow negative feedback in model respiratory neurons. CHAOS (WOODBURY, N.Y.) 2024; 34:063131. [PMID: 38865093 PMCID: PMC11191356 DOI: 10.1063/5.0201472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Accepted: 05/24/2024] [Indexed: 06/13/2024]
Abstract
Recordings from pre-Bötzinger complex neurons responsible for the inspiratory phase of the respiratory rhythm reveal a ramping burst pattern, starting around the time that the transition from expiration to inspiration begins, in which the spike rate gradually rises until a transition into a high-frequency burst occurs. The spike rate increase along the burst is accompanied by a gradual depolarization of the plateau potential that underlies the spikes. These effects may be functionally important for inducing the onset of inspiration and hence maintaining effective respiration; however, most mathematical models for inspiratory bursting do not capture this activity pattern. Here, we study how the modulation of spike height and afterhyperpolarization via the slow inactivation of an inward current can support various activity patterns including ramping bursts. We use dynamical systems methods designed for multiple timescale systems, such as bifurcation analysis based on timescale decomposition and averaging over fast oscillations, to generate an understanding of and predictions about the specific dynamic effects that lead to ramping bursts. We also analyze how transitions between ramping and other activity patterns may occur with parameter changes, which could be associated with experimental manipulations, environmental conditions, and/or development.
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Affiliation(s)
- Sushmita R. John
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| | - Ryan S. Phillips
- Seattle Children’s Research Institute, Seattle, Washington 98109, USA
| | - Jonathan E. Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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7
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Chen JL, Kuo CC. Inhibition of resurgent Na + currents by rufinamide. Neuropharmacology 2024; 247:109835. [PMID: 38228283 DOI: 10.1016/j.neuropharm.2024.109835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 12/29/2023] [Accepted: 12/31/2023] [Indexed: 01/18/2024]
Abstract
Na+ channels are essential for the genesis of action potentials in most neurons. After opening by membrane depolarization, Na+ channels enter a series of inactivated states (e.g. the fast, intermediate, and slow inactivated states; or If, Ii, and Is). The inactivated Na+ channel may recover via the open state upon membrane repolarization, giving rise to "resurgent" Na+ currents which could be critical for densely repetitive or burst discharges. We incubated CHO-K1 cells transfected with human NaV1.7 cDNA and measured resurgent currents with whole-cell patch recordings. We found Ii is the major inactivated state responsible for the genesis of resurgent currents. Rufinamide, in therapeutic concentrations, could selectively bind to Ii to slow the recovery process and dose-dependently inhibit resurgent currents. The other Na+ channel-inhibiting antiseizure medications (ASM), such as phenytoin and lacosamide (selectively binds to If and Is, separately), fail to show a similar inhibitory effect in clinically relevant concentrations. Resurgent currents are decreased with lengthening of the prepulse, presumably because of redistribution of the channel from Ii to If. Rufinamide could accentuate the decrease to mimic a use-dependent inhibitory effect. The molecular action of slowing of recovery from inactivation by binding to Ii also explains the highly correlative inhibitory effect of rufinamide on both transient and resurgent Na+ currents. The modest but correlative inhibition of both currents may make a novel synergistic effect and thus strong-enough suppression of pathological repetitive and especially burst discharges. Rufinamide may thus have a unique spectrum of therapeutic applications for disorders with excessive neural excitabilities.
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Affiliation(s)
- Jian-Lin Chen
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan.
| | - Chung-Chin Kuo
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan; Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan.
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8
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Monteil A, Guérineau NC, Gil-Nagel A, Parra-Diaz P, Lory P, Senatore A. New insights into the physiology and pathophysiology of the atypical sodium leak channel NALCN. Physiol Rev 2024; 104:399-472. [PMID: 37615954 DOI: 10.1152/physrev.00014.2022] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 07/13/2023] [Accepted: 08/15/2023] [Indexed: 08/25/2023] Open
Abstract
Cell excitability and its modulation by hormones and neurotransmitters involve the concerted action of a large repertoire of membrane proteins, especially ion channels. Unique complements of coexpressed ion channels are exquisitely balanced against each other in different excitable cell types, establishing distinct electrical properties that are tailored for diverse physiological contributions, and dysfunction of any component may induce a disease state. A crucial parameter controlling cell excitability is the resting membrane potential (RMP) set by extra- and intracellular concentrations of ions, mainly Na+, K+, and Cl-, and their passive permeation across the cell membrane through leak ion channels. Indeed, dysregulation of RMP causes significant effects on cellular excitability. This review describes the molecular and physiological properties of the Na+ leak channel NALCN, which associates with its accessory subunits UNC-79, UNC-80, and NLF-1/FAM155 to conduct depolarizing background Na+ currents in various excitable cell types, especially neurons. Studies of animal models clearly demonstrate that NALCN contributes to fundamental physiological processes in the nervous system including the control of respiratory rhythm, circadian rhythm, sleep, and locomotor behavior. Furthermore, dysfunction of NALCN and its subunits is associated with severe pathological states in humans. The critical involvement of NALCN in physiology is now well established, but its study has been hampered by the lack of specific drugs that can block or agonize NALCN currents in vitro and in vivo. Molecular tools and animal models are now available to accelerate our understanding of how NALCN contributes to key physiological functions and the development of novel therapies for NALCN channelopathies.
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Affiliation(s)
- Arnaud Monteil
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France
- LabEx "Ion Channel Science and Therapeutics," Montpellier, France
- Department of Physiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Nathalie C Guérineau
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France
- LabEx "Ion Channel Science and Therapeutics," Montpellier, France
| | - Antonio Gil-Nagel
- Department of Neurology, Epilepsy Program, Hospital Ruber Internacional, Madrid, Spain
| | - Paloma Parra-Diaz
- Department of Neurology, Epilepsy Program, Hospital Ruber Internacional, Madrid, Spain
| | - Philippe Lory
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France
- LabEx "Ion Channel Science and Therapeutics," Montpellier, France
| | - Adriano Senatore
- Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada
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9
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Raman IM. The Hodgkin-Huxley-Katz Prize Lecture: A Markov model with permeation-dependent gating that accounts for resurgent current of voltage-gated Na channels. J Physiol 2023; 601:5147-5164. [PMID: 37837315 PMCID: PMC10913027 DOI: 10.1113/jp285166] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Accepted: 09/20/2023] [Indexed: 10/16/2023] Open
Abstract
Many neurons that fire high-frequency action potentials express specialized voltage-gated Na channel complexes that not only conduct transient current upon depolarization, but also pass resurgent current upon repolarization. The resurgent current is associated with recovery of transient current, even at moderately negative potentials where fast inactivation is usually absorbing. The combined results of many experimental studies have led to the hypothesis that resurgent current flows upon repolarization when an endogenous blocking protein that occludes open channels at depolarized potentials is expelled by inwardly permeating Na ions. Additional observations have suggested that the position of the voltage sensor of domain IV regulates the affinity of the channel for the putative blocker. To test the effectiveness of a kinetic scheme incorporating these features, here we develop and justify a Markov model with states grounded in known Na channel conformations. Simulations were designed to investigate whether including a permeation-dependent unblocking rate constant and two open-blocked states, superimposed on conformations and voltage-sensitive movements present in all voltage-gated Na channels, is sufficient to account for the unusual gating of channels with a resurgent component. Optimizing rate constant parameters against a wide range of experimental data from cerebellar Purkinje cells demonstrates that a kinetic scheme for Na channels incorporating the novel aspects of a permeation-dependent unblock, as well as distinct high- and low-affinity blocked states, reproduces all the attributes of experimentally recorded Na currents in a physiologically plausible manner.
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Affiliation(s)
- Indira M Raman
- Department of Neurobiology, Northwestern University, Evanston, IL, USA
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10
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Kelly JJ, Wen H, Brehm P. Single-cell RNAseq analysis of spinal locomotor circuitry in larval zebrafish. eLife 2023; 12:RP89338. [PMID: 37975797 PMCID: PMC10656102 DOI: 10.7554/elife.89338] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023] Open
Abstract
Identification of the neuronal types that form the specialized circuits controlling distinct behaviors has benefited greatly from the simplicity offered by zebrafish. Electrophysiological studies have shown that in addition to connectivity, understanding of circuitry requires identification of functional specializations among individual circuit components, such as those that regulate levels of transmitter release and neuronal excitability. In this study, we use single-cell RNA sequencing (scRNAseq) to identify the molecular bases for functional distinctions between motoneuron types that are causal to their differential roles in swimming. The primary motoneuron, in particular, expresses high levels of a unique combination of voltage-dependent ion channel types and synaptic proteins termed functional 'cassettes.' The ion channel types are specialized for promoting high-frequency firing of action potentials and augmented transmitter release at the neuromuscular junction, both contributing to greater power generation. Our transcriptional profiling of spinal neurons further assigns expression of this cassette to specific interneuron types also involved in the central circuitry controlling high-speed swimming and escape behaviors. Our analysis highlights the utility of scRNAseq in functional characterization of neuronal circuitry, in addition to providing a gene expression resource for studying cell type diversity.
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Affiliation(s)
- Jimmy J Kelly
- Vollum Institute, Oregon Health & Science UniversityPortlandUnited States
| | - Hua Wen
- Vollum Institute, Oregon Health & Science UniversityPortlandUnited States
| | - Paul Brehm
- Vollum Institute, Oregon Health & Science UniversityPortlandUnited States
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11
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Shiau AL, Lee KH, Cho HY, Chuang TH, Yu MC, Wu CL, Wu SN. Molnupiravir, a ribonucleoside antiviral prodrug against SARS-CoV-2, alters the voltage-gated sodium current and causes adverse events. Virology 2023; 587:109865. [PMID: 37572519 DOI: 10.1016/j.virol.2023.109865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 08/02/2023] [Accepted: 08/04/2023] [Indexed: 08/14/2023]
Abstract
Molnupiravir (MOL) is a ribonucleoside prodrug for oral treatment of COVID-19. Common adverse effects of MOL are headache, diarrhea, and nausea, which may be associated with altered sodium channel function. Here, we investigated the effect of MOL on voltage-gated Na+ current (INa) in pituitary GH3 cells. We show that MOL had distinct effects on transient and late INa, in combination with decreased time constant in the slow component of INa inactivation. The 50% inhibitory concentration (IC50) values of MOL for suppressing transient and late INa were 26.1 and 6.3 μM, respectively. The overall steady-state current-voltage relationship of INa remained unchanged upon MOL exposure. MOL-induced alteration of INa may lead to changes in physiological function through sodium channels. Apart from its effect on inhibiting RNA virus replication, MOL exerts inhibitory effects on plasmalemma INa, which might constitute an additional yet crucial underlying mechanism of its pharmacological activity or adverse events.
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Affiliation(s)
- Ai-Li Shiau
- Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi City, 60002, Taiwan; Department of Microbiology and Immunology, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan
| | - Kuan-Hsien Lee
- Department of Emergency Medicine, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi City, 60002, Taiwan
| | - Hsin-Yen Cho
- Department of Physiology, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan
| | - Tzu-Hsien Chuang
- Department of Physiology, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan
| | - Meng-Cheng Yu
- Department of Physiology, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan
| | - Chao-Liang Wu
- Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi City, 60002, Taiwan; Department of Biochemistry and Molecular Biology, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan.
| | - Sheng-Nan Wu
- Department of Physiology, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan; School of Medicine, College of Medicine, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan.
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12
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Kelly JJ, Wen H, Brehm P. Single cell RNA-seq analysis of spinal locomotor circuitry in larval zebrafish. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.543939. [PMID: 37333232 PMCID: PMC10274715 DOI: 10.1101/2023.06.06.543939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Identification of the neuronal types that form the specialized circuits controlling distinct behaviors has benefited greatly from the simplicity offered by zebrafish. Electrophysiological studies have shown that additional to connectivity, understanding of circuitry requires identification of functional specializations among individual circuit components, such as those that regulate levels of transmitter release and neuronal excitability. In this study we use single cell RNA sequencing (scRNAseq) to identify the molecular bases for functional distinctions between motoneuron types that are causal to their differential roles in swimming. The primary motoneuron (PMn) in particular, expresses high levels of a unique combination of voltage-dependent ion channel types and synaptic proteins termed functional 'cassettes'. The ion channel types are specialized for promoting high frequency firing of action potentials and augmented transmitter release at the neuromuscular junction, both contributing to greater power generation. Our transcriptional profiling of spinal neurons further assigns expression of this cassette to specific interneuron types also involved in the central circuitry controlling high speed swimming and escape behaviors. Our analysis highlights the utility of scRNAseq in functional characterization of neuronal circuitry, in addition to providing a gene expression resource for studying cell type diversity.
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Affiliation(s)
- Jimmy J. Kelly
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA
| | - Hua Wen
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA
| | - Paul Brehm
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA
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13
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Soeda S, Ito D, Ogushi T, Sano Y, Negoro R, Fujita T, Saito R, Taniura H. Defects in early synaptic formation and neuronal function in Prader-Willi syndrome. Sci Rep 2023; 13:12053. [PMID: 37491450 PMCID: PMC10368700 DOI: 10.1038/s41598-023-39065-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 07/19/2023] [Indexed: 07/27/2023] Open
Abstract
Prader-Willi syndrome (PWS), which is a complex epigenetic disorder caused by the deficiency of paternally expressed genes in chromosome 15q11-q13, is associated with several psychiatric dimensions, including autism spectrum disorder. We have previously reported that iPS cells derived from PWS patients exhibited aberrant differentiation and transcriptomic dysregulation in differentiated neural stem cells (NSCs) and neurons. Here, we identified SLITRK1 as a downregulated gene in NSCs differentiated from PWS patient iPS cells by RNA sequencing analysis. Because SLITRK1 is involved in synaptogenesis, we focused on the synaptic formation and function of neurons differentiated from PWS patient iPS cells and NDN or MAGEL2 single gene defect mutant iPS cells. Although βIII tubulin expression levels in all the neurons were comparable to the level of differentiation in the control, pre- and postsynaptic markers were significantly lower in PWS and mutant neurons than in control neurons. PSD-95 puncta along βIII tubulin neurites were also decreased. Membrane potential responses were measured while exposed to high K+ stimulation. The neuronal excitabilities in PWS and mutant neurons showed significantly lower intensity than that of control neurons. These functional defects in PWS neurons may reflect phenotypes of neurodevelopmental disorders in PWS.
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Affiliation(s)
- Shuhei Soeda
- Laboratory of Neurochemistry, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga, 525-8577, Japan.
| | - Daiki Ito
- Laboratory of Neurochemistry, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga, 525-8577, Japan
| | - Tomoe Ogushi
- Laboratory of Neurochemistry, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga, 525-8577, Japan
| | - Yui Sano
- Laboratory of Neurochemistry, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga, 525-8577, Japan
| | - Ryosuke Negoro
- Laboratory of Molecular Pharmacokinetics, College of Pharmaceutical Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan
| | - Takuya Fujita
- Laboratory of Molecular Pharmacokinetics, College of Pharmaceutical Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan
| | - Ryo Saito
- Mitsubishi Tanabe Pharma Corporation, Kamoshida, Aoba, Yokohama, 227-0033, Japan
| | - Hideo Taniura
- Laboratory of Neurochemistry, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga, 525-8577, Japan
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Structure of human Na V1.6 channel reveals Na + selectivity and pore blockade by 4,9-anhydro-tetrodotoxin. Nat Commun 2023; 14:1030. [PMID: 36823201 PMCID: PMC9950489 DOI: 10.1038/s41467-023-36766-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 02/15/2023] [Indexed: 02/25/2023] Open
Abstract
The sodium channel NaV1.6 is widely expressed in neurons of the central and peripheral nervous systems, which plays a critical role in regulating neuronal excitability. Dysfunction of NaV1.6 has been linked to epileptic encephalopathy, intellectual disability and movement disorders. Here we present cryo-EM structures of human NaV1.6/β1/β2 alone and complexed with a guanidinium neurotoxin 4,9-anhydro-tetrodotoxin (4,9-ah-TTX), revealing molecular mechanism of NaV1.6 inhibition by the blocker. The apo-form structure reveals two potential Na+ binding sites within the selectivity filter, suggesting a possible mechanism for Na+ selectivity and conductance. In the 4,9-ah-TTX bound structure, 4,9-ah-TTX binds to a pocket similar to the tetrodotoxin (TTX) binding site, which occupies the Na+ binding sites and completely blocks the channel. Molecular dynamics simulation results show that subtle conformational differences in the selectivity filter affect the affinity of TTX analogues. Taken together, our results provide important insights into NaV1.6 structure, ion conductance, and inhibition.
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15
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Abstract
Voltage-gated sodium channel Nav1.6 plays a crucial role in neuronal firing in the central nervous system (CNS). Aberrant function of Nav1.6 may lead to epilepsy and other neurological disorders. Specific inhibitors of Nav1.6 thus have therapeutic potentials. Here we present the cryo-EM structure of human Nav1.6 in the presence of auxiliary subunits β1 and fibroblast growth factor homologous factor 2B (FHF2B) at an overall resolution of 3.1 Å. The overall structure represents an inactivated state with closed pore domain (PD) and all "up" voltage-sensing domains. A conserved carbohydrate-aromatic interaction involving Trp302 and Asn326, together with the β1 subunit, stabilizes the extracellular loop in repeat I. Apart from regular lipids that are resolved in the EM map, an unprecedented Y-shaped density that belongs to an unidentified molecule binds to the PD, revealing a potential site for developing Nav1.6-specific blockers. Structural mapping of disease-related Nav1.6 mutations provides insights into their pathogenic mechanism.
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Inhibition of Voltage-Gated Na + Currents Exerted by KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea), an Inhibitor of Na +-Ca 2+ Exchanging Process. Int J Mol Sci 2023; 24:ijms24021805. [PMID: 36675319 PMCID: PMC9864174 DOI: 10.3390/ijms24021805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 12/21/2022] [Accepted: 01/13/2023] [Indexed: 01/18/2023] Open
Abstract
KB-R7943, an isothiourea derivative, has been recognized as an inhibitor in the reverse mode of the Na+-Ca2+ exchanging process. This compound was demonstrated to prevent intracellular Na+-dependent Ca2+ uptake in intact cells; however, it is much less effective at preventing extracellular Na+-dependent Ca2+ efflux. Therefore, whether or how this compound may produce any perturbations on other types of ionic currents, particularly on voltage-gated Na+ current (INa), needs to be further studied. In this study, the whole-cell current recordings demonstrated that upon abrupt depolarization in pituitary GH3 cells, the exposure to KB-R7943 concentration-dependently depressed the transient (INa(T)) or late component (INa(L)) of INa with an IC50 value of 11 or 0.9 μM, respectively. Likewise, the dissociation constant for the KB-R7943-mediated block of INa on the basis of a minimum reaction scheme was estimated to be 0.97 μM. The presence of benzamil or amiloride could suppress the INa(L) magnitude. The instantaneous window Na+ current (INa(W)) activated by abrupt ascending ramp voltage (Vramp) was suppressed by adding KB-R7943; however, subsequent addition of deltamethrin or tefluthrin (Tef) effectively reversed KB-R7943-inhibted INa(W). With prolonged duration of depolarizing pulses, the INa(L) amplitude became exponentially decreased; moreover, KB-R7943 diminished INa(L) magnitude. The resurgent Na+ current (INa(R)) evoked by a repolarizing Vramp was also suppressed by adding this compound; moreover, subsequent addition of ranolazine or Tef further diminished or reversed, respectively, its reduction in INa(R) magnitude. The persistent Na+ current (INa(P)) activated by sinusoidal voltage waveform became enhanced by Tef; however, subsequent application of KB-R7943 counteracted Tef-stimulated INa(P). The docking prediction reflected that there seem to be molecular interactions of this molecule with the hNaV1.2 or hNaV1.7 channels. Collectively, this study highlights evidence showing that KB-R7943 has the propensity to perturb the magnitude and gating kinetics of INa (e.g., INa(T), INa(L), INa(W), INa(R), and INa(P)) and that the NaV channels appear to be important targets for the in vivo actions of KB-R7943 or other relevant compounds.
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17
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Effraim PR, Estacion M, Zhao P, Sosniak D, Waxman SG, Dib-Hajj SD. Fibroblast growth factor homologous factor 2 attenuates excitability of DRG neurons. J Neurophysiol 2022; 128:1258-1266. [PMID: 36222860 PMCID: PMC9909838 DOI: 10.1152/jn.00361.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Fibroblast growth factor homologous factors (FHFs) are cytosolic members of the superfamily of the FGF proteins. Four members of this subfamily (FHF1-4) are differentially expressed in multiple tissues in an isoform-dependent manner. Mutations in FHF proteins have been associated with multiple neurological disorders. FHF proteins bind to the COOH terminus of voltage-gated sodium (Nav) channels and regulate current amplitude and gating properties of these channels. FHF2, which is expressed in dorsal root ganglia (DRG) neurons, has two main splicing isoforms: FHF2A and FHF2B, which differ in the length and sequence of their NH2 termini, have been shown to differentially regulate gating properties of Nav1.7, a channel that is a major driver of DRG neuron firing. FHF2 expression levels are downregulated after peripheral nerve axotomy, which suggests that they may regulate neuronal excitability via an action on Nav channels after injury. We have previously shown that knockdown of FHF2 leads to gain-of-function changes in Nav1.7 gating properties: enhanced repriming, increased current density, and hyperpolarized activation. From this we posited that knockdown of FHF2 might also lead to DRG hyperexcitability. Here we show that knockdown of either FHF2A alone or all isoforms of FHF2 results in increased DRG neuron excitability. In addition, we demonstrate that supplementation of FHF2A and FHF2B reduces DRG neuron excitability. Overexpression of FHF2A or FHF2B also reduced excitability of DRG neurons treated with a cocktail of inflammatory mediators, a model of inflammatory pain. Our data suggest that increased neuronal excitability after nerve injury might be triggered, in part, via a loss of FHF2-Nav1.7 interaction.NEW & NOTEWORTHY FHF2 is known to bind to and modulate the function of Nav1.7. FHF2 expression is also reduced after nerve injury. We demonstrate that knockdown of FHF2 expression increases DRG neuronal excitability. More importantly, overexpression of FHF2 reduces DRG excitability in basal conditions and in the presence of inflammatory mediators (a model of inflammatory pain). These results suggest that FHF2 could potentially be used as a tool to reduce DRG neuronal excitability and to treat pain.
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Affiliation(s)
- Philip R. Effraim
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06510
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Mark Estacion
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Peng Zhao
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Daniel Sosniak
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Stephen G Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Sulayman D. Dib-Hajj
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA
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18
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Elleman AV, Du Bois J. Chemical and Biological Tools for the Study of Voltage-Gated Sodium Channels in Electrogenesis and Nociception. Chembiochem 2022; 23:e202100625. [PMID: 35315190 PMCID: PMC9359671 DOI: 10.1002/cbic.202100625] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 02/22/2022] [Indexed: 12/17/2022]
Abstract
The malfunction and misregulation of voltage-gated sodium channels (NaV s) underlie in large part the electrical hyperexcitability characteristic of chronic inflammatory and neuropathic pain. NaV s are responsible for the initiation and propagation of electrical impulses (action potentials) in cells. Tissue and nerve injury alter the expression and localization of multiple NaV isoforms, including NaV 1.1, 1.3, and 1.6-1.9, resulting in aberrant action potential firing patterns. To better understand the role of NaV regulation, localization, and trafficking in electrogenesis and pain pathogenesis, a number of chemical and biological reagents for interrogating NaV function have been advanced. The development and application of such tools for understanding NaV physiology are the focus of this review.
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Affiliation(s)
- Anna V Elleman
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - J Du Bois
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
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19
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Richardson A, Ciampani V, Stancu M, Bondarenko K, Newton S, Steinert JR, Pilati N, Graham BP, Kopp-Scheinpflug C, Forsythe ID. Kv3.3 subunits control presynaptic action potential waveform and neurotransmitter release at a central excitatory synapse. eLife 2022; 11:75219. [PMID: 35510987 PMCID: PMC9110028 DOI: 10.7554/elife.75219] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 04/29/2022] [Indexed: 11/29/2022] Open
Abstract
Kv3 potassium currents mediate rapid repolarisation of action potentials (APs), supporting fast spikes and high repetition rates. Of the four Kv3 gene family members, Kv3.1 and Kv3.3 are highly expressed in the auditory brainstem and we exploited this to test for subunit-specific roles at the calyx of Held presynaptic terminal in the mouse. Deletion of Kv3.3 (but not Kv3.1) reduced presynaptic Kv3 channel immunolabelling, increased presynaptic AP duration and facilitated excitatory transmitter release; which in turn enhanced short-term depression during high-frequency transmission. The response to sound was delayed in the Kv3.3KO, with higher spontaneous and lower evoked firing, thereby reducing signal-to-noise ratio. Computational modelling showed that the enhanced EPSC and short-term depression in the Kv3.3KO reflected increased vesicle release probability and accelerated activity-dependent vesicle replenishment. We conclude that Kv3.3 mediates fast repolarisation for short precise APs, conserving transmission during sustained high-frequency activity at this glutamatergic excitatory synapse.
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Affiliation(s)
- Amy Richardson
- epartment of Neuroscience, Psychology and Behaviour, University of Leicester, Leicester, United Kingdom
| | - Victoria Ciampani
- epartment of Neuroscience, Psychology and Behaviour, University of Leicester, Leicester, United Kingdom
| | - Mihai Stancu
- Division of Neurobiology, Ludwig-Maximilians-Universität München, Munchen, Germany
| | - Kseniia Bondarenko
- epartment of Neuroscience, Psychology and Behaviour, University of Leicester, Leicester, United Kingdom
| | - Sherylanne Newton
- epartment of Neuroscience, Psychology and Behaviour, University of Leicester, Leicester, United Kingdom
| | - Joern R Steinert
- epartment of Neuroscience, Psychology and Behaviour, University of Leicester, Leicester, United Kingdom
| | - Nadia Pilati
- Istituto di Ricerca Pediatrica Citta'della Speranza, Padova, Italy
| | - Bruce P Graham
- Computing Science and Mathematics, University of Stirling, Stirling, United Kingdom
| | | | - Ian D Forsythe
- epartment of Neuroscience, Psychology and Behaviour, University of Leicester, Leicester, United Kingdom
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20
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Xiao Y, Theile JW, Zybura A, Pan Y, Lin Z, Cummins TR. A-type FHFs mediate resurgent currents through TTX-resistant voltage-gated sodium channels. eLife 2022; 11:77558. [PMID: 35441593 PMCID: PMC9071269 DOI: 10.7554/elife.77558] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Accepted: 04/19/2022] [Indexed: 11/13/2022] Open
Abstract
Resurgent currents (INaR) produced by voltage-gated sodium channels are required for many neurons to maintain high-frequency firing, and contribute to neuronal hyperexcitability and disease pathophysiology. Here we show, for the first time, that INaR can be reconstituted in a heterologous system by co-expression of sodium channel α-subunits and A-type fibroblast growth factor homologous factors (FHFs). Specifically, A-type FHFs induces INaR from Nav1.8, Nav1.9 tetrodotoxin-resistant neuronal channels and, to a lesser extent, neuronal Nav1.7 and cardiac Nav1.5 channels. Moreover, we identified the N-terminus of FHF as the critical molecule responsible for A-type FHFs-mediated INaR. Among the FHFs, FHF4A is the most important isoform for mediating Nav1.8 and Nav1.9 INaR. In nociceptive sensory neurons, FHF4A knockdown significantly reduces INaR amplitude and the percentage of neurons that generate INaR, substantially suppressing excitability. Thus, our work reveals a novel molecular mechanism underlying TTX-resistant INaR generation and provides important potential targets for pain treatment.
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Affiliation(s)
- Yucheng Xiao
- Biology Department, Indiana University - Purdue University Indianapolis, Indianapolis, United States
| | | | - Agnes Zybura
- Paul and Carole Stark Neurosciences Research Institute, Indiana University, Indianapolis, United States
| | - Yanling Pan
- Biology Department, Indiana University - Purdue University Indianapolis, Indianapolis, United States
| | | | - Theodore R Cummins
- Biology Department, Indiana University - Purdue University Indianapolis, Indianapolis, United States
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21
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Kinetic Alterations in Resurgent Sodium Currents of Mutant Nav1.4 Channel in Two Patients Affected by Paramyotonia Congenita. BIOLOGY 2022; 11:biology11040613. [PMID: 35453812 PMCID: PMC9031228 DOI: 10.3390/biology11040613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Revised: 04/11/2022] [Accepted: 04/14/2022] [Indexed: 11/17/2022]
Abstract
Simple Summary Paramyotonia congenita (PMC) is a rare muscle disorder that causes myotonia and weakness of facial and limb muscles. The electromyography in PMC shows continual spontaneous, high-frequency spike potentials in skeletal muscles. Genetic mutations in the Nav1.4 channel that cause hyperexcitability of muscle fibers are responsible for PMC. However, the genotype–phenotype relationship is highly diversified, and the molecular pathology remains unclear. Here, we investigated the electrophysiology in the Nav1.4 channel with mutations, p.V781I and p.A1737T, which were found in two Taiwanese patients. We identified the distinct changes in gating mechanisms altered by mutations which may underlie the clinical phenotype. Abstract Paramyotonia congenita (PMC) is a rare skeletal muscle disorder characterized by muscle stiffness upon repetitive exercise and cold exposure. PMC was reported to be caused by dominant mutations in the SCN4A gene encoding the α subunit of the Nav1.4 channel. Recently, we identified two missense mutations of the SCN4A gene, p.V781I and p.A1737T, in two PMC families. To evaluate the changes in electrophysiological properties caused by the mutations, both mutant and wild-type (WT) SCN4A genes were expressed in CHO-K1 and HEK-293T cells. Then, whole-cell patch-clamp recording was employed to study the altered gating of mutant channels. The activation curve of transient current showed a hyperpolarizing shift in both mutant Nav1.4 channels as compared to the WT channel, whereas there was a depolarizing shift in the fast inactivation curve. These changes confer to an increase in window current in the mutant channels. Further investigations demonstrated that the mutated channel proteins generate significantly larger resurgent currents as compared to the WT channel and take longer to attain the peak of resurgent current than the WT channel. In conclusion, the current study demonstrates that p.V781I and p.A1737T mutations in the Nav1.4 channel increase both the sustained and the resurgent Na+ current, leading to membrane hyperexcitability with a lower firing threshold, which may influence the clinical phenotype.
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22
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The Evidence for Effective Inhibition of INa Produced by Mirogabalin ((1R,5S,6S)-6-(aminomethyl)-3-ethyl-bicyclo [3.2.0] hept-3-ene-6-acetic acid), a Known Blocker of Ca V Channels. Int J Mol Sci 2022; 23:ijms23073845. [PMID: 35409204 PMCID: PMC8998350 DOI: 10.3390/ijms23073845] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 03/28/2022] [Accepted: 03/29/2022] [Indexed: 01/27/2023] Open
Abstract
Mirogabalin (MGB, Tarlige®), an inhibitor of the α2δ-1 subunit of voltage-gated Ca2+ (CaV) channels, is used as a way to alleviate peripheral neuropathic pain and diabetic neuropathy. However, to what extent MGB modifies the magnitude, gating, and/or hysteresis of various types of plasmalemmal ionic currents remains largely unexplored. In pituitary tumor (GH3) cells, we found that MGB was effective at suppressing the peak (transient, INa(T)) and sustained (late, INa(L)) components of the voltage-gated Na+ current (INa) in a concentration-dependent manner, with an effective IC50 of 19.5 and 7.3 μM, respectively, while the KD value calculated on the basis of minimum reaction scheme was 8.2 μM. The recovery of INa(T) inactivation slowed in the presence of MGB, although the overall current-voltage relation of INa(T) was unaltered; however, there was a leftward shift in the inactivation curve of the current. The magnitude of the window (INa(W)) or resurgent INa (INa(R)) evoked by the respective ascending or descending ramp pulse (Vramp) was reduced during cell exposure to MGB. MGB-induced attenuation in INa(W) or INa(R) was reversed by the further addition of tefluthrin, a pyrethroid insecticide known to stimulate INa. MGB also effectively lessened the strength of voltage-dependent hysteresis of persistent INa in response to the isosceles triangular Vramp. The cumulative inhibition of INa(T), evoked by pulse train stimulation, was enhanced in its presence. Taken together, in addition to the inhibition of CaV channels, the NaV channel attenuation produced by MGB might have an impact in its analgesic effects occurring in vivo.
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23
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Cho HY, Chen PC, Chuang TH, Yu MC, Wu SN. Activation of Voltage-Gated Na+ Current by GV-58, a Known Activator of CaV Channels. Biomedicines 2022; 10:biomedicines10030721. [PMID: 35327523 PMCID: PMC8945347 DOI: 10.3390/biomedicines10030721] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 03/10/2022] [Accepted: 03/17/2022] [Indexed: 02/04/2023] Open
Abstract
GV-58 ((2R)-2-[(6-{[(5-methylthiophen-2-yl)methyl]amino}-9-propyl-9H-purin-2-yl)amino]butan-1-ol) is recognized to be an activator of N- and P/Q-type Ca2+ currents. However, its modulatory actions on other types of ionic currents in electrically excitable cells remain largely unanswered. This study was undertaken to explore the possible modifications caused by GV-58 in ionic currents (e.g., voltage-gated Na+ current [INa], A-type K+ current [IK(A)], and erg-mediated K+ current [IK(erg)]) identified from pituitary GH3 lactotrophs. GH3 cell exposure to GV-58 enhanced the transient and late components of INa with varying potencies; consequently, the EC50 values of GV-58 required for its differential increase in peak and late INa in GH3 cells were estimated to be 8.9 and 2.6 μM, respectively. The INa in response to brief depolarizing pulse was respectively stimulated or suppressed by GV-58 or tetrodotoxin, but it failed to be altered by ω-conotoxin MVIID. Cell exposure to this compound increased the recovery of INa inactivation evoked by two-pulse protocol based on a geometrics progression; however, in its presence, there was a slowing in the inactivation rate of current decay evoked by a train of depolarizing pulses. The existence of GV-58 also resulted in an increase in the amplitude of ramp-induced resurgent and window INa. The presence of this compound inhibited IK(A) magnitude, accompanied by a shortening in inactivation time course of the current; however, it mildly decreased IK(erg). Under current-clamp conditions, GV-58 increased the frequency of spontaneous action potentials in GH3 cells. Moreover, in NSC-34 motor neuron-like cells, the presence of GV-58 not only raised INa amplitude but also reduced current inactivation. Taken together, the overall work provides a noticeable yet unidentified finding which implies that, in addition to its agonistic effect on Ca2+ currents, GV-58 may concertedly modify the amplitude and gating kinetics of INa in electrically excitable cells, hence modifiying functional activities in these cells.
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Affiliation(s)
- Hsin-Yen Cho
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
| | - Pei-Chun Chen
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan City 70101, Taiwan
| | - Tzu-Hsien Chuang
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
| | - Meng-Cheng Yu
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
| | - Sheng-Nan Wu
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan City 70101, Taiwan
- Correspondence: ; Tel.: +886-6-2353535-5334; Fax: +886-6-2362780
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24
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Ransdell JL, Moreno JD, Bhagavan D, Silva JR, Nerbonne JM. Intrinsic mechanisms in the gating of resurgent Na + currents. eLife 2022; 11:70173. [PMID: 35076394 PMCID: PMC8824471 DOI: 10.7554/elife.70173] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Accepted: 01/24/2022] [Indexed: 11/13/2022] Open
Abstract
The 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.
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Affiliation(s)
- Joseph L Ransdell
- Department of Medicine, Washington University in Saint Louis, Saint Louis, United States
| | - Jonathan D Moreno
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, United States
| | - Druv Bhagavan
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, United States
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, Saint Louis, United States
| | - Jeanne M Nerbonne
- Department of Medicine, Washington University in Saint Louis, Saint Louis, United States
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25
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The Evidence for Sparsentan-Mediated Inhibition of INa and IK(erg): Possibly Unlinked to Its Antagonism of Angiotensin II or Endothelin Type a Receptor. Biomedicines 2021; 10:biomedicines10010086. [PMID: 35052766 PMCID: PMC8773265 DOI: 10.3390/biomedicines10010086] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 12/22/2021] [Accepted: 12/29/2021] [Indexed: 12/19/2022] Open
Abstract
Sparsentan is viewed as a dual antagonist of endothelin type A (ETA) receptor and angiotensin II (AngII) receptor and it could be beneficial in patients with focal segmental glomerulosclerosis. Moreover, it could improve glomerular filtration rate and augment protective tissue remodeling in mouse models of focal segmental glomerulosclerosis. The ionic mechanisms through which it interacts with the magnitude and/or gating kinetics of ionic currents in excitable cells were not thoroughly investigated. Herein, we aimed to examine the effects of varying sparsentan concentrations on ionic currents residing in pituitary GH3 somatolactotrophs. From whole-cell current recordings made in GH3 cells, sparsentan (0.3–100 μM) differentially inhibited the peak and late components of voltage-gated Na+ current (INa). The IC50 value of sparsentan required to exert a reduction in peak and late INa in GH3 cells was 15.04 and 1.21 μM, respectively; meanwhile, the KD value estimated from its shortening in the slow component of INa inactivation time constant was 2.09 μM. The sparsentan (10 μM) presence did not change the overall current–voltage relationship of INa; however, the steady-state inactivation curve of the current was shifted to more negative potential in its presence (10 μM), with no change in the gating charge of the curve. The window INa activated by a brief upsloping ramp was decreased during exposure to sparsentan (10 μM); moreover, recovery of peak INa became slowed in its presence. The Tefluthrin (Tef)-stimulated resurgent INa activated in response to abrupt depolarization followed by the descending ramp pulse was additionally attenuated by subsequent application of sparsentan. In continued presence of Tef (3 μM) or β-pompilidotoxin (3 μM), further application of sparsentan (3 μM) reversed their stimulation of INa. However, sparsentan-induced inhibition of INa failed to be overcome by subsequent application of either endothelin 1 (1 μM) or angiotensin II (1 μM); moreover, in continued presence of endothelin (1 μM) or angiotensin II (1 μM), further addition of sparsentan (3 μM) effectively decreased peak INa. Additionally, the application of sparsentan (3 μM) inhibited the peak and late components of erg-mediated K+ current in GH3 cells, although it mildly decreased the amplitude of delayed-rectifier K+ current. Altogether, this study provides a distinct yet unidentified finding that sparsentan may perturb the amplitude or gating of varying ionic currents in excitable cells.
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Xu C, Zhang Y, Gozal D, Carney P. Channelopathy of Dravet Syndrome and Potential Neuroprotective Effects of Cannabidiol. J Cent Nerv Syst Dis 2021; 13:11795735211048045. [PMID: 34992485 PMCID: PMC8724990 DOI: 10.1177/11795735211048045] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Dravet syndrome (DS) is a channelopathy, neurodevelopmental, epileptic encephalopathy characterized by seizures, developmental delay, and cognitive impairment that includes susceptibility to thermally induced seizures, spontaneous seizures, ataxia, circadian rhythm and sleep disorders, autistic-like behaviors, and premature death. More than 80% of DS cases are linked to mutations in genes which encode voltage-gated sodium channel subunits, SCN1A and SCN1B, which encode the Nav1.1α subunit and Nav1.1β1 subunit, respectively. There are other gene mutations encoding potassium, calcium, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels related to DS. One-third of patients have pharmacoresistance epilepsy. DS is unresponsive to standard therapy. Cannabidiol (CBD), a non-psychoactive phytocannabinoid present in Cannabis, has been introduced for treating DS because of its anticonvulsant properties in animal models and humans, especially in pharmacoresistant patients. However, the etiological channelopathiological mechanism of DS and action mechanism of CBD on the channels are unclear. In this review, we summarize evidence of the direct and indirect action mechanism of sodium, potassium, calcium, and HCN channels in DS, especially sodium subunits. Some channels' loss-of-function or gain-of-function in inhibitory or excitatory neurons determine the balance of excitatory and inhibitory are associated with DS. A great variety of mechanisms of CBD anticonvulsant effects are focused on modulating these channels, especially sodium, calcium, and potassium channels, which will shed light on ionic channelopathy of DS and the precise molecular treatment of DS in the future.
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Affiliation(s)
- Changqing Xu
- Department of Child Health and the Child Health Research Institute, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Yumin Zhang
- Department of Anatomy, Physiology and Genetics; Department of Neuroscience, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - David Gozal
- Department of Child Health and the Child Health Research Institute, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Paul Carney
- Departments of Child Health and Neurology, School of Medicine, University of Missouri, Columbia, MO, USA
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Resurgent Na + currents promote ultrafast spiking in projection neurons that drive fine motor control. Nat Commun 2021; 12:6762. [PMID: 34799550 PMCID: PMC8604930 DOI: 10.1038/s41467-021-26521-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 10/08/2021] [Indexed: 11/29/2022] Open
Abstract
The underlying mechanisms that promote precise spiking in upper motor neurons controlling fine motor skills are not well understood. Here we report that projection neurons in the adult zebra finch song nucleus RA display robust high-frequency firing, ultra-narrow spike waveforms, superfast Na+ current inactivation kinetics, and large resurgent Na+ currents (INaR). These properties of songbird pallial motor neurons closely resemble those of specialized large pyramidal neurons in mammalian primary motor cortex. They emerge during the early phases of song development in males, but not females, coinciding with a complete switch of Na+ channel subunit expression from Navβ3 to Navβ4. Dynamic clamping and dialysis of Navβ4's C-terminal peptide into juvenile RA neurons provide evidence that Navβ4, and its associated INaR, promote neuronal excitability. We thus propose that INaR modulates the excitability of upper motor neurons that are required for the execution of fine motor skills.
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Quattrocolo G, Dunville K, Nigro MJ. Resurgent Sodium Current in Neurons of the Cerebral Cortex. Front Cell Neurosci 2021; 15:760610. [PMID: 34658797 PMCID: PMC8517112 DOI: 10.3389/fncel.2021.760610] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 09/13/2021] [Indexed: 11/29/2022] Open
Abstract
In the late ’90, Dr. Indira Raman, at the time a postdoctoral fellow with Dr. Bruce Bean, at Harvard University, identified a new type of sodium current, flowing through the channels that reopens when the membrane is repolarized. This current, called “resurgent Sodium current,” was originally identified in cerebellar Purkinje neurons and has now been confirmed in around 20 different neuronal types. Since moving to Northwestern University in 1999 to establish her own research group, Dr. Raman has dedicated great efforts in identifying the mechanisms supporting the resurgent Sodium current and how its biophysical properties shape the firing of the different cell types. Her work has impacted greatly the field of cellular neurophysiology, from basic research to translation neuroscience. In fact, alterations in the resurgent sodium currents have been observed in several neuropathologies, from Huntington’s disease to epilepsy. In this Perspective we will focus on the current knowledge on the expression and function of the resurgent Sodium current in neurons of the cerebral cortex and hippocampus. We will also briefly highlight the role of Dr. Raman’s as teacher and mentor, not only for her pupils, but for the whole scientific community.
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Affiliation(s)
- Giulia Quattrocolo
- Center for Neural Computation, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
| | - Keagan Dunville
- Center for Neural Computation, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
| | - Maximiliano José Nigro
- Center for Neural Computation, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
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Meredith FL, Rennie KJ. Dopaminergic Inhibition of Na + Currents in Vestibular Inner Ear Afferents. Front Neurosci 2021; 15:710321. [PMID: 34580582 PMCID: PMC8463658 DOI: 10.3389/fnins.2021.710321] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Accepted: 08/10/2021] [Indexed: 11/13/2022] Open
Abstract
Inner ear hair cells form synapses with afferent terminals and afferent neurons carry signals as action potentials to the central nervous system. Efferent neurons have their origins in the brainstem and some make synaptic contact with afferent dendrites beneath hair cells. Several neurotransmitters have been identified that may be released from efferent terminals to modulate afferent activity. Dopamine is a candidate efferent neurotransmitter in both the vestibular and auditory systems. Within the cochlea, activation of dopamine receptors may reduce excitotoxicity at the inner hair cell synapse via a direct effect of dopamine on afferent terminals. Here we investigated the effect of dopamine on sodium currents in acutely dissociated vestibular afferent calyces to determine if dopaminergic signaling could also modulate vestibular responses. Calyx terminals were isolated along with their accompanying type I hair cells from the cristae of gerbils (P15-33) and whole cell patch clamp recordings performed. Large transient sodium currents were present in all isolated calyces; compared to data from crista slices, resurgent Na+ currents were rare. Perfusion of dopamine (100 μM) in the extracellular solution significantly reduced peak transient Na+ currents by approximately 20% of control. A decrease in Na+ current amplitude was also seen with extracellular application of the D2 dopamine receptor agonist quinpirole, whereas the D2 receptor antagonist eticlopride largely abolished the response to dopamine. Inclusion of the phosphatase inhibitor okadaic acid in the patch electrode solution occluded the response to dopamine. The reduction in calyx sodium current in response to dopamine suggests efferent signaling through D2 dopaminergic receptors may occur via common mechanisms to decrease excitability in inner ear afferents.
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Affiliation(s)
- Frances L Meredith
- Department of Otolaryngology - Head & Neck Surgery, School of Medicine, University of Colorado, Aurora, CO, United States
| | - Katherine J Rennie
- Department of Otolaryngology - Head & Neck Surgery, School of Medicine, University of Colorado, Aurora, CO, United States.,Department of Physiology & Biophysics, School of Medicine, University of Colorado, Aurora, CO, United States
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Platholi J, Hemmings HC. Effects of general anesthetics on synaptic transmission and plasticity. Curr Neuropharmacol 2021; 20:27-54. [PMID: 34344292 PMCID: PMC9199550 DOI: 10.2174/1570159x19666210803105232] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 07/26/2021] [Accepted: 08/02/2021] [Indexed: 11/22/2022] Open
Abstract
General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.
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Affiliation(s)
- Jimcy Platholi
- Cornell University Joan and Sanford I Weill Medical College Ringgold standard institution - Anesthesiology New York, New York. United States
| | - Hugh C Hemmings
- Cornell University Joan and Sanford I Weill Medical College Ringgold standard institution - Anesthesiology New York, New York. United States
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Dvorak NM, Wadsworth PA, Wang P, Zhou J, Laezza F. Development of Allosteric Modulators of Voltage-Gated Na + Channels: A Novel Approach for an Old Target. Curr Top Med Chem 2021; 21:841-848. [PMID: 34036922 DOI: 10.2174/1568026621666210525105359] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 05/11/2021] [Accepted: 05/11/2021] [Indexed: 12/12/2022]
Abstract
Given their primacy in governing the action potential (AP) of excitable cells, voltage-gated Na+ (Nav) channels are important pharmacological targets of therapeutics for a diverse array of clinical indications. Despite historically being a traditional drug target, therapeutics targeting Nav channels lack isoform selectivity, giving rise to off-target side effects. To develop isoform-selective modulators of Nav channels with improved target-specificity, the identification and pharmacological targeting of allosteric sites that display structural divergence among Nav channel isoforms represents an attractive approach. Despite the high homology among Nav channel α subunit isoforms (Nav1.1-Nav1.9), there is considerable amino acid sequence divergence among their constituent C-terminal domains (CTD), which enables structurally and functionally specific protein: protein interactions (PPI) with auxiliary proteins. Although pharmacological targeting of such PPI interfaces between the CTDs of Nav channels and auxiliary proteins represents an innovate approach for developing isoform-selective modulators of Nav channels, appreciable modulation of PPIs using small molecules has conventionally been difficult to achieve. After briefly discussing the challenges of modulating PPIs using small molecules, this current frontier review that follows subsequently expounds on approaches for circumventing such difficulties in the context of developing small molecule modulators of PPIs between transmembrane ion channels and their auxiliary proteins. In addition to broadly discussing such approaches, the implementation of such approaches is specifically discussed in the context of developing small molecule modulators between the CTD of Nav channels and auxiliary proteins. Developing allosteric modulators of ion channels by targeting their PPI interfaces with auxiliary proteins represents an innovative and promising strategy in ion channel drug discovery that could expand the "druggable genome" and usher in first-in-class PPI-targeting therapeutics for a multitude of channelopathies.
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Affiliation(s)
- Nolan M Dvorak
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, 77555, United States
| | - Paul A Wadsworth
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, 77555, United States
| | - Pingyuan Wang
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, 77555, United States
| | - Jia Zhou
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, 77555, United States
| | - Fernanda Laezza
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, 77555, United States
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32
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Deng Y, Wang H, Joni M, Sekhri R, Reiner A. Progression of basal ganglia pathology in heterozygous Q175 knock-in Huntington's disease mice. J Comp Neurol 2021; 529:1327-1371. [PMID: 32869871 PMCID: PMC8049038 DOI: 10.1002/cne.25023] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 08/07/2020] [Accepted: 08/26/2020] [Indexed: 12/29/2022]
Abstract
We used behavioral testing and morphological methods to detail the progression of basal ganglia neuron type-specific pathology and the deficits stemming from them in male heterozygous Q175 mice, compared to age-matched WT males. A rotarod deficit was not present in Q175 mice until 18 months, but increased open field turn rate (reflecting hyperkinesia) and open field anxiety were evident at 6 months. No loss of striatal neurons was seen out to 18 months, but ENK+ and DARPP32+ striatal perikarya were fewer by 6 months, due to diminished expression, with further decline by 18 months. No reduction in SP+ striatal perikarya or striatal interneurons was seen in Q175 mice at 18 months, but cholinergic interneurons showed dendrite attenuation by 6 months. Despite reduced ENK expression in indirect pathway striatal perikarya, ENK-immunostained terminals in globus pallidus externus (GPe) were more abundant at 6 months and remained so out to 18 months. Similarly, SP-immunostained terminals from striatal direct pathway neurons were more abundant in globus pallidus internus and substantia nigra at 6 months and remained so at 18 months. FoxP2+ arkypallidal GPe neurons and subthalamic nucleus neurons were lost by 18 months but not prototypical PARV+ GPe neurons or dopaminergic nigral neurons. Our results show that striatal projection neuron abnormalities and behavioral abnormalities reflecting them develop between 2 and 6 months of age in Q175 male heterozygotes, indicating early effects of the HD mutation. The striatal pathologies resemble those in human HD, but are less severe at 18 months than even in premanifest HD.
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Affiliation(s)
- Yunping Deng
- Department of Anatomy and NeurobiologyThe University of Tennessee Health Science CenterMemphisTennesseeUSA
| | - Hongbing Wang
- Department of Anatomy and NeurobiologyThe University of Tennessee Health Science CenterMemphisTennesseeUSA
| | - Marion Joni
- Department of Anatomy and NeurobiologyThe University of Tennessee Health Science CenterMemphisTennesseeUSA
| | - Radhika Sekhri
- Department of PathologyThe University of Tennessee Health Science CenterMemphisTennesseeUSA
| | - Anton Reiner
- Department of Anatomy and NeurobiologyThe University of Tennessee Health Science CenterMemphisTennesseeUSA
- Department of OphthalmologyThe University of Tennessee Health Science CenterMemphisTennesseeUSA
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Mantegazza M, Cestèle S, Catterall WA. Sodium channelopathies of skeletal muscle and brain. Physiol Rev 2021; 101:1633-1689. [PMID: 33769100 DOI: 10.1152/physrev.00025.2020] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Voltage-gated sodium channels initiate action potentials in nerve, skeletal muscle, and other electrically excitable cells. Mutations in them cause a wide range of diseases. These channelopathy mutations affect every aspect of sodium channel function, including voltage sensing, voltage-dependent activation, ion conductance, fast and slow inactivation, and both biosynthesis and assembly. Mutations that cause different forms of periodic paralysis in skeletal muscle were discovered first and have provided a template for understanding structure, function, and pathophysiology at the molecular level. More recent work has revealed multiple sodium channelopathies in the brain. Here we review the well-characterized genetics and pathophysiology of the periodic paralyses of skeletal muscle and then use this information as a foundation for advancing our understanding of mutations in the structurally homologous α-subunits of brain sodium channels that cause epilepsy, migraine, autism, and related comorbidities. We include studies based on molecular and structural biology, cell biology and physiology, pharmacology, and mouse genetics. Our review reveals unexpected connections among these different types of sodium channelopathies.
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Affiliation(s)
- Massimo Mantegazza
- Université Cote d'Azur, Valbonne-Sophia Antipolis, France.,CNRS UMR7275, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne-Sophia Antipolis, France.,INSERM, Valbonne-Sophia Antipolis, France
| | - Sandrine Cestèle
- Université Cote d'Azur, Valbonne-Sophia Antipolis, France.,CNRS UMR7275, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne-Sophia Antipolis, France
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Binda F, Valente P, Marte A, Baldelli P, Benfenati F. Increased responsiveness at the cerebellar input stage in the PRRT2 knockout model of paroxysmal kinesigenic dyskinesia. Neurobiol Dis 2021; 152:105275. [PMID: 33515674 DOI: 10.1016/j.nbd.2021.105275] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 01/24/2021] [Accepted: 01/24/2021] [Indexed: 02/07/2023] Open
Abstract
PRoline-Rich Transmembrane protein-2 (PRRT2) is a recently described neuron-specific type-2 integral membrane protein with a large cytosolic N-terminal domain that distributes in presynaptic and axonal domains where it interacts with several presynaptic proteins and voltage-gated Na+ channels. Several PRRT2 mutations are the main cause of a wide and heterogeneous spectrum of paroxysmal disorders with a loss-of-function pathomechanism. The highest expression levels of PRRT2 in brain occurs in cerebellar granule cells (GCs) and cerebellar dysfunctions participate in the dyskinetic phenotype of PRRT2 knockout (KO) mice. We have investigated the effects of PRRT2 deficiency on the intrinsic excitability of GCs and the input-output relationships at the mossy fiber-GC synapses. We show that PRRT2 KO primary GCs display increased expression of Na+ channels, increased amplitude of Na+ currents and increased length of the axon initial segment, leading to an overall enhancement of intrinsic excitability. In acute PRRT2 KO cerebellar slices, GCs were more prone to action potential discharge in response to mossy fiber activation and exhibited an enhancement of transient and persistent Na+ currents, in the absence of changes at the mossy fiber-GC synapses. The results support a key role of PRRT2 expressed in GCs in the physiological regulation of the excitatory input to the cerebellum and are consistent with a major role of a cerebellar dysfunction in the pathogenesis of the PRRT2-linked paroxysmal pathologies.
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Affiliation(s)
- Francesca Binda
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132 Genova, Italy
| | - Pierluigi Valente
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132 Genova, Italy; IRCCS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132 Genova, Italy
| | - Antonella Marte
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132 Genova, Italy
| | - Pietro Baldelli
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132 Genova, Italy; IRCCS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132 Genova, Italy
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132 Genova, Italy; IRCCS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132 Genova, Italy.
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35
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Armstrong CM, Hollingworth S. Na + and K + channels: history and structure. Biophys J 2021; 120:756-763. [PMID: 33484711 DOI: 10.1016/j.bpj.2021.01.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 01/10/2021] [Accepted: 01/12/2021] [Indexed: 11/27/2022] Open
Abstract
In this perspective, we discuss the physiological roles of Na and K channels, emphasizing the importance of the K channel for cellular homeostasis in animal cells and of Na and K channels for cellular signaling. We consider the structural basis of Na and K channel gating in light of recent structural and electrophysiological findings.
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Affiliation(s)
- Clay M Armstrong
- Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Stephen Hollingworth
- Undergraduate Neuroscience Program, University of Pennsylvania, Philadelphia, Pennsylvania.
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Changes in Resurgent Sodium Current Contribute to the Hyperexcitability of Muscles in Patients with Paramyotonia Congenita. Biomedicines 2021; 9:biomedicines9010051. [PMID: 33430134 PMCID: PMC7826575 DOI: 10.3390/biomedicines9010051] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 01/01/2021] [Accepted: 01/06/2021] [Indexed: 11/17/2022] Open
Abstract
Paramyotonia congenita (PMC) is a rare hereditary skeletal muscle disorder. The major symptom, muscle stiffness, is frequently induced by cold exposure and repetitive exercise. Mutations in human SCN4A gene, which encodes the α-subunit of Nav1.4 channel, are responsible for PMC. Mutation screening of SCN4A gene from two PMC families identified two missense mutations, p.T1313M and p.R1448H. To elucidate the electrophysiological abnormalities caused by the mutations, the p.T1313M, p.R1448H, and wild-type (WT) SCN4A genes were transient expressed on Chinese hamster ovary (CHO-K1) cells. The detailed study on the gating defects of the mutant channels using the whole-cell patch clamping technique was performed. The mutant Nav1.4 channels impaired the basic gating properties with increasing sustained and window currents during membrane depolarization and facilitated the genesis of resurgent currents during repolarization. The mutations caused a hyperpolarization shift in the fast inactivation and slightly enhanced the slow inactivation with an increase in half-maximal inactivation voltage. No differences were found in the decay kinetics of the tail current between mutant and WT channels. In addition to generating the larger resurgent sodium current, the time to peak in the mutant channels was longer than that in the WT channels. In conclusion, our results demonstrated that the mutations p.T1313M and p.R1448H in Nav1.4 channels can enhance fast inactivation, slow inactivation, and resurgent current, revealing that subtle changes in gating processes can influence the clinical phenotype.
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Ravenscroft TA, Janssens J, Lee PT, Tepe B, Marcogliese PC, Makhzami S, Holmes TC, Aerts S, Bellen HJ. Drosophila Voltage-Gated Sodium Channels Are Only Expressed in Active Neurons and Are Localized to Distal Axonal Initial Segment-like Domains. J Neurosci 2020; 40:7999-8024. [PMID: 32928889 PMCID: PMC7574647 DOI: 10.1523/jneurosci.0142-20.2020] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 07/15/2020] [Accepted: 08/04/2020] [Indexed: 12/28/2022] Open
Abstract
In multipolar vertebrate neurons, action potentials (APs) initiate close to the soma, at the axonal initial segment. Invertebrate neurons are typically unipolar with dendrites integrating directly into the axon. Where APs are initiated in the axons of invertebrate neurons is unclear. Voltage-gated sodium (NaV) channels are a functional hallmark of the axonal initial segment in vertebrates. We used an intronic Minos-Mediated Integration Cassette to determine the endogenous gene expression and subcellular localization of the sole NaV channel in both male and female Drosophila, para Despite being the only NaV channel in the fly, we show that only 23 ± 1% of neurons in the embryonic and larval CNS express para, while in the adult CNS para is broadly expressed. We generated a single-cell transcriptomic atlas of the whole third instar larval brain to identify para expressing neurons and show that it positively correlates with markers of differentiated, actively firing neurons. Therefore, only 23 ± 1% of larval neurons may be capable of firing NaV-dependent APs. We then show that Para is enriched in an axonal segment, distal to the site of dendritic integration into the axon, which we named the distal axonal segment (DAS). The DAS is present in multiple neuron classes in both the third instar larval and adult CNS. Whole cell patch clamp electrophysiological recordings of adult CNS fly neurons are consistent with the interpretation that Nav-dependent APs originate in the DAS. Identification of the distal NaV localization in fly neurons will enable more accurate interpretation of electrophysiological recordings in invertebrates.SIGNIFICANCE STATEMENT The site of action potential (AP) initiation in invertebrates is unknown. We tagged the sole voltage-gated sodium (NaV) channel in the fly, para, and identified that Para is enriched at a distal axonal segment. The distal axonal segment is located distal to where dendrites impinge on axons and is the likely site of AP initiation. Understanding where APs are initiated improves our ability to model neuronal activity and our interpretation of electrophysiological data. Additionally, para is only expressed in 23 ± 1% of third instar larval neurons but is broadly expressed in adults. Single-cell RNA sequencing of the third instar larval brain shows that para expression correlates with the expression of active, differentiated neuronal markers. Therefore, only 23 ± 1% of third instar larval neurons may be able to actively fire NaV-dependent APs.
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Affiliation(s)
- Thomas A Ravenscroft
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030
| | - Jasper Janssens
- VIB Center for Brain & Disease Research, KU Leuven, Leuven 3000, Belgium
- Department of Human Genetics, KU Leuven, Leuven 3000, Belgium
| | - Pei-Tseng Lee
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030
| | - Burak Tepe
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030
| | - Paul C Marcogliese
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030
| | - Samira Makhzami
- VIB Center for Brain & Disease Research, KU Leuven, Leuven 3000, Belgium
- Department of Human Genetics, KU Leuven, Leuven 3000, Belgium
| | - Todd C Holmes
- Department of Physiology and Biophysics, School of Medicine, University of California at Irvine, Irvine, California 92697
| | - Stein Aerts
- VIB Center for Brain & Disease Research, KU Leuven, Leuven 3000, Belgium
- Department of Human Genetics, KU Leuven, Leuven 3000, Belgium
| | - Hugo J Bellen
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030
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Werginz P, Raghuram V, Fried SI. Tailoring of the axon initial segment shapes the conversion of synaptic inputs into spiking output in OFF-α T retinal ganglion cells. SCIENCE ADVANCES 2020; 6:6/37/eabb6642. [PMID: 32917708 PMCID: PMC7486099 DOI: 10.1126/sciadv.abb6642] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Accepted: 07/29/2020] [Indexed: 06/11/2023]
Abstract
Recently, mouse OFF-α transient (OFF-α T) retinal ganglion cells (RGCs) were shown to display a gradient of light responses as a function of position along the dorsal-ventral axis; response differences were correlated to differences in the level of excitatory presynaptic input. Here, we show that postsynaptic differences between cells also make a strong contribution to response differences. Cells in the dorsal retina had longer axon initial segments (AISs)-the greater number of Nav1.6 channels in longer AISs directly mediates higher rates of spiking and helps avoid depolarization block that terminates spiking in ventral cells with shorter AISs. The pre- and postsynaptic specializations that shape the output of OFF-α T RGCs interact in different ways: In dorsal cells, strong inputs and the long AISs are both necessary to generate their strong, sustained spiking outputs, while in ventral cells, weak inputs or the short AISs are both sufficient to limit the spiking signal.
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Affiliation(s)
- Paul Werginz
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
- Institute for Analysis and Scientific Computing, Vienna University of Technology, 1040 Vienna, Austria
| | - Vineeth Raghuram
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
- Boston VA Healthcare System, Rehabilitation, Research and Development, Boston, MA 02130, USA
- Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA
| | - Shelley I Fried
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
- Boston VA Healthcare System, Rehabilitation, Research and Development, Boston, MA 02130, USA
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Menezes LFS, Sabiá Júnior EF, Tibery DV, Carneiro LDA, Schwartz EF. Epilepsy-Related Voltage-Gated Sodium Channelopathies: A Review. Front Pharmacol 2020; 11:1276. [PMID: 33013363 PMCID: PMC7461817 DOI: 10.3389/fphar.2020.01276] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 07/31/2020] [Indexed: 12/29/2022] Open
Abstract
Epilepsy is a disease characterized by abnormal brain activity and a predisposition to generate epileptic seizures, leading to neurobiological, cognitive, psychological, social, and economic impacts for the patient. There are several known causes for epilepsy; one of them is the malfunction of ion channels, resulting from mutations. Voltage-gated sodium channels (NaV) play an essential role in the generation and propagation of action potential, and malfunction caused by mutations can induce irregular neuronal activity. That said, several genetic variations in NaV channels have been described and associated with epilepsy. These mutations can affect channel kinetics, modifying channel activation, inactivation, recovery from inactivation, and/or the current window. Among the NaV subtypes related to epilepsy, NaV1.1 is doubtless the most relevant, with more than 1500 mutations described. Truncation and missense mutations are the most observed alterations. In addition, several studies have already related mutated NaV channels with the electrophysiological functioning of the channel, aiming to correlate with the epilepsy phenotype. The present review provides an overview of studies on epilepsy-associated mutated human NaV1.1, NaV1.2, NaV1.3, NaV1.6, and NaV1.7.
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Affiliation(s)
- Luis Felipe Santos Menezes
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil
| | - Elias Ferreira Sabiá Júnior
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil
| | - Diogo Vieira Tibery
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil
| | - Lilian Dos Anjos Carneiro
- Faculdade de Medicina, Centro Universitário Euro Americano, Brasília, Brazil.,Faculdade de Medicina, Centro Universitário do Planalto Central, Brasília, Brazil
| | - Elisabeth Ferroni Schwartz
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil
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Muralidharan M, Guo T, Shivdasani MN, Tsai D, Fried S, Li L, Dokos S, Morley JW, Lovell NH. Neural activity of functionally different retinal ganglion cells can be robustly modulated by high-rate electrical pulse trains. J Neural Eng 2020; 17:045013. [DOI: 10.1088/1741-2552/ab9a97] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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41
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Meredith FL, Rennie KJ. Persistent and resurgent Na + currents in vestibular calyx afferents. J Neurophysiol 2020; 124:510-524. [PMID: 32667253 DOI: 10.1152/jn.00124.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Vestibular afferent neurons convey information from hair cells in the peripheral vestibular end organs to central nuclei. Primary vestibular afferent neurons can fire action potentials at high rates and afferent firing patterns vary with the position of nerve terminal endings in vestibular neuroepithelia. Terminals contact hair cells as small bouton or large calyx endings. To investigate the role of Na+ currents (INa) in firing mechanisms, we investigated biophysical properties of INa in calyx-bearing afferents. Whole cell patch-clamp recordings were made from calyx terminals in thin slices of gerbil crista at different postnatal ages: immature [postnatal day (P)5-P8, young (P13-P15), and mature (P30-P45)]. A large transient Na+ current (INaT) was completely blocked by 300 nM tetrodotoxin (TTX) in mature calyces. In addition, INaT was accompanied by much smaller persistent Na+ currents (INaP) and distinctive resurgent Na+ currents (INaR), which were also blocked by TTX. ATX-II, a toxin that slows Na+ channel inactivation, enhanced INaP in immature and mature calyces. 4,9-Anhydro-TTX (4,9-ah-TTX), which selectively blocks Nav1.6 channels, abolished the enhanced INa in mature, but not immature, calyces. Therefore, Nav1.6 channels mediate a component of INaT and INaP in mature calyces, but are minimally expressed at early postnatal days. INaR was expressed in less than one-third of calyces at P6-P8, but expression increased with development, and in mature cristae INaR was frequently found in peripheral calyces. INaR served to increase the availability of Na+ channels following brief membrane depolarizations. In current clamp, the rate and regularity of action potential firing decreased in mature peripheral calyces following 4,9-ah-TTX application. Therefore, Nav1.6 channels are upregulated during development, contribute to INaT, INaP, and INaR, and may regulate excitability by enabling higher mean discharge rates in a subpopulation of mature calyx afferents.NEW & NOTEWORTHY Action potential firing patterns differ between groups of afferent neurons innervating vestibular epithelia. We investigated the biophysical properties of Na+ currents in specialized vestibular calyx afferent terminals during postnatal development. Mature calyces express Na+ currents with transient, persistent, and resurgent components. Nav1.6 channels contribute to resurgent Na+ currents and may enhance firing in peripheral calyx afferents. Understanding Na+ channels that contribute to vestibular nerve responses has implications for developing new treatments for vestibular dysfunction.
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Affiliation(s)
- Frances L Meredith
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, Colorado
| | - Katherine J Rennie
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, Colorado.,Department of Physiology & Biophysics, University of Colorado School of Medicine, Aurora, Colorado
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Ohtsuki G, Shishikura M, Ozaki A. Synergistic excitability plasticity in cerebellar functioning. FEBS J 2020; 287:4557-4593. [PMID: 32367676 DOI: 10.1111/febs.15355] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Revised: 04/22/2020] [Accepted: 04/30/2020] [Indexed: 12/27/2022]
Abstract
The cerebellum, a universal processor for sensory acquisition and internal models, and its association with synaptic and nonsynaptic plasticity have been envisioned as the biological correlates of learning, perception, and even thought. Indeed, the cerebellum is no longer considered merely as the locus of motor coordination and its learning. Here, we introduce the mechanisms underlying the induction of multiple types of plasticity in cerebellar circuit and give an overview focusing on the plasticity of nonsynaptic intrinsic excitability. The discovery of long-term potentiation of synaptic responsiveness in hippocampal neurons led investigations into changes of their intrinsic excitability. This activity-dependent potentiation of neuronal excitability is distinct from that of synaptic efficacy. Systematic examination of excitability plasticity has indicated that the modulation of various types of Ca2+ - and voltage-dependent K+ channels underlies the phenomenon, which is also triggered by immune activity. Intrinsic plasticity is expressed specifically on dendrites and modifies the integrative processing and filtering effect. In Purkinje cells, modulation of the discordance of synaptic current on soma and dendrite suggested a novel type of cellular learning mechanism. This property enables a plausible synergy between synaptic efficacy and intrinsic excitability, by amplifying electrical conductivity and influencing the polarity of bidirectional synaptic plasticity. Furthermore, the induction of intrinsic plasticity in the cerebellum correlates with motor performance and cognitive processes, through functional connections from the cerebellar nuclei to neocortex and associated regions: for example, thalamus and midbrain. Taken together, recent advances in neuroscience have begun to shed light on the complex functioning of nonsynaptic excitability and the synergy.
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Affiliation(s)
- Gen Ohtsuki
- The Hakubi Center for Advanced Research, Kyoto University, Japan.,Department of Biophysics, Kyoto University Graduate School of Science, Japan.,Department of Drug Discovery Medicine, Kyoto University Graduate School of Medicine, Japan
| | - Mari Shishikura
- Department of Biophysics, Kyoto University Graduate School of Science, Japan
| | - Akitoshi Ozaki
- Department of Biophysics, Kyoto University Graduate School of Science, Japan
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Thull S, Neacsu C, O'Reilly AO, Bothe S, Hausmann R, Huth T, Meents J, Lampert A. Mechanism underlying hooked resurgent-like tail currents induced by an insecticide in human cardiac Nav1.5. Toxicol Appl Pharmacol 2020; 397:115010. [PMID: 32302602 DOI: 10.1016/j.taap.2020.115010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 04/12/2020] [Accepted: 04/14/2020] [Indexed: 01/02/2023]
Abstract
Voltage-gated sodium channels are responsible not only for the fast upstroke of the action potential, but they also modify cellular excitability via persistent and resurgent currents. Insecticides act via permanently opening sodium channels to immobilize the animals. Cellular recordings performed decades ago revealed distinctly hooked tail currents induced by these compounds. Here, we applied the classical type-II pyrethroid deltamethrin on human cardiac Nav1.5 and observed resurgent-like currents at very negative potentials in the absence of any pore-blocker, which resemble those hooked tail currents. We show that deltamethrin dramatically slows both fast inactivation and deactivation of Nav1.5 and thereby induces large persistent currents. Using the sea anemone toxin ATx-II as a tool to prevent all inactivation-related processes, resurgent-like currents were eliminated while persistent currents were preserved. Our experiments suggest that, in deltamethrin-modified channels, recovery from inactivation occurs faster than delayed deactivation, opening a brief window for sodium influx and leading to hooked, resurgent-like currents, in the absence of an open channel blocker. Thus, we now explain with pharmacological methods the biophysical gating changes underlying the deltamethrin induced hooked tail currents. SUMMARY: The pyrethroid deltamethrin induces hooked resurgent-like tail currents in human cardiac voltage-gated Nav1.5 channels. Using deltamethrin and ATx-II, we identify additional conducting channel states caused by a faster recovery from inactivation compared to the deltamethrin-induced delayed deactivation.
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Affiliation(s)
- Sarah Thull
- Institute of Physiology, RWTH Aachen University, Pauwelsstr. 30, 52074 Aachen, Germany
| | - Cristian Neacsu
- Institut für Physiologie und Pathophysiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitaetsstr. 17, 91054 Erlangen, Germany
| | - Andrias O O'Reilly
- School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, UK
| | - Stefanie Bothe
- Institute of Physiology, RWTH Aachen University, Pauwelsstr. 30, 52074 Aachen, Germany; Research Training Group 2416 MultiSenses-MultiScales, RWTH Aachen University, Aachen, Germany
| | - Ralf Hausmann
- Institute of Clinical Pharmacology, RWTH Aachen University, Wendlingweg 2, 52074 Aachen, Germany
| | - Tobias Huth
- Institut für Physiologie und Pathophysiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitaetsstr. 17, 91054 Erlangen, Germany
| | - Jannis Meents
- Institute of Physiology, RWTH Aachen University, Pauwelsstr. 30, 52074 Aachen, Germany.
| | - Angelika Lampert
- Institute of Physiology, RWTH Aachen University, Pauwelsstr. 30, 52074 Aachen, Germany; Research Training Group 2416 MultiSenses-MultiScales, RWTH Aachen University, Aachen, Germany; Research Training Group 2415 ME3T, RWTH Aachen University, Aachen, Germany.
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Changes of Resurgent Na + Currents in the Na v1.4 Channel Resulting from an SCN4A Mutation Contributing to Sodium Channel Myotonia. Int J Mol Sci 2020; 21:ijms21072593. [PMID: 32276507 PMCID: PMC7177622 DOI: 10.3390/ijms21072593] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 03/30/2020] [Accepted: 04/06/2020] [Indexed: 12/19/2022] Open
Abstract
Myotonia congenita (MC) is a rare disorder characterized by stiffness and weakness of the limb and trunk muscles. Mutations in the SCN4A gene encoding the alpha-subunit of the voltage-gated sodium channel Nav1.4 have been reported to be responsible for sodium channel myotonia (SCM). The Nav1.4 channel is expressed in skeletal muscles, and its related channelopathies affect skeletal muscle excitability, which can manifest as SCM, paramyotonia and periodic paralysis. In this study, the missense mutation p.V445M was identified in two individual families with MC. To determine the functional consequences of having a mutated Nav1.4 channel, whole-cell patch-clamp recording of transfected Chinese hamster ovary cells was performed. Evaluation of the transient Na+ current found that a hyperpolarizing shift occurs at both the activation and inactivation curves with an increase of the window currents in the mutant channels. The Nav1.4 channel's co-expression with the Navβ4 peptide can generate resurgent Na+ currents at repolarization following a depolarization. The magnitude of the resurgent currents is higher in the mutant than in the wild-type (WT) channel. Although the decay kinetics are comparable between the mutant and WT channels, the time to the peak of resurgent Na+ currents in the mutant channel is significantly protracted compared with that in the WT channel. These findings suggest that the p.V445M mutation in the Nav1.4 channel results in an increase of both sustained and resurgent Na+ currents, which may contribute to hyperexcitability with repetitive firing and is likely to facilitate recurrent myotonia in SCM patients.
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Ohtsuki G. Modification of Synaptic-Input Clustering by Intrinsic Excitability Plasticity on Cerebellar Purkinje Cell Dendrites. J Neurosci 2020; 40:267-282. [PMID: 31754008 PMCID: PMC6948944 DOI: 10.1523/jneurosci.3211-18.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 10/08/2019] [Accepted: 10/24/2019] [Indexed: 02/06/2023] Open
Abstract
The role of dendrites in the integration of widespread synaptic activity has been studied in experiments and theories (Johnston et al., 1996; Magee, 2007). However, whether the conduction of synaptic currents from dendrites to the soma depends on excitability of those dendritic branches is unclear. How modulation of the branch excitability affects the conduction of synaptic inputs and their selection on dendrites is also elusive. Here, I performed simultaneous voltage-clamp recordings from the soma and dendrites of single cerebellar Purkinje neurons in male Sprague-Dawley rats and analyzed the relationship between spontaneous EPSCs on both sides. I found that EPSCs on distal dendrites have a salient discordance in amplitude compared with those on the soma. Furthermore, individual ratios of the EPSC concurrently recorded on the soma and dendrites were not unique, but discrete, suggesting the occurrence of various attenuations in different paths of dendritic branches to the soma. The obtained data and simulations indicate several distinct groups (4.5 ± 0.3, n = 22 somatodendritic recordings) of co-occurred synaptic inputs in Purkinje cell dendrites. This clustering of synaptic currents was suggested to emerge at farther distances than the secondary bifurcations. Finally, ratios of the co-EPSCs were uniformly distributed after either intrinsic plasticity induction or SK-channel blockade. Overall, results suggest that in Purkinje cells the excitability along the dendrite processes modulates the conduction of EPSCs and makes active inputs heterogeneous through SK channel activity, intrinsic plasticity, and dendritic branching. These properties of dendrites may confer branch-specific computational power to neurons.SIGNIFICANCE STATEMENT I have previously studied the "non-synaptic" plasticity of the intrinsic excitability in the cerebellar Purkinje cells (Belmeguenai et al., 2010), and branch-specific increase of intrinsic excitability of the dendrites (Ohtsuki et al., 2012b; Ohtsuki and Hansel, 2018) through the downregulation of SK (small conductance Ca2+-activated K+) channels. In this study, I show that a dendritic filtering of synaptic electroconductivity is heterogeneous among the branches on distal dendrites and that the increase in the dendritic excitability accompanied with the intrinsic plasticity alters a state with the heterogeneity to a globally excitable state in Purkinje neurons. My findings propose a new learning model relying on the intrinsic excitability plasticity of the dendritic branch fields.
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Affiliation(s)
- Gen Ohtsuki
- The Hakubi Center for Advanced Research, Kyoto University, Yoshida, Sakyo-ward, Kyoto 606-8501, Japan, and
- Department of Biophysics, Kyoto University Graduate School of Science, Kitashirakawa-Oiwake-cho, Sakyo-ward, Kyoto 606-8224, Japan
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Isoflurane Modulates Hippocampal Cornu Ammonis Pyramidal Neuron Excitability by Inhibition of Both Transient and Persistent Sodium Currents in Mice. Anesthesiology 2020; 131:94-104. [PMID: 31166240 DOI: 10.1097/aln.0000000000002753] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Volatile anesthetics inhibit presynaptic voltage-gated sodium channels to reduce neurotransmitter release, but their effects on excitatory neuron excitability by sodium current inhibition are unclear. The authors hypothesized that inhibition of transient and persistent neuronal sodium currents by the volatile anesthetic isoflurane contributes to reduced hippocampal pyramidal neuron excitability. METHODS Whole-cell patch-clamp recordings of sodium currents of hippocampal cornu ammonis pyramidal neurons were performed in acute mouse brain slices. The actions of isoflurane on both transient and persistent sodium currents were analyzed at clinically relevant concentrations of isoflurane. RESULTS The median inhibitory concentration of isoflurane for inhibition of transient sodium currents was 1.0 ± 0.3 mM (~3.7 minimum alveolar concentration [MAC]) from a physiologic holding potential of -70 mV. Currents from a hyperpolarized holding potential of -120 mV were minimally inhibited (median inhibitory concentration = 3.6 ± 0.7 mM, ~13.3 MAC). Isoflurane (0.55 mM; ~2 MAC) shifted the voltage-dependence of steady-state inactivation by -6.5 ± 1.0 mV (n = 11, P < 0.0001), but did not affect the voltage-dependence of activation. Isoflurane increased the time constant for sodium channel recovery from 7.5 ± 0.6 to 12.7 ± 1.3 ms (n = 13, P < 0.001). Isoflurane also reduced persistent sodium current density (median inhibitory concentration = 0.4 ± 0.1 mM, ~1.5 MAC) and resurgent currents. Isoflurane (0.55 mM; ~2 MAC) reduced action potential amplitude, and hyperpolarized resting membrane potential from -54.6 ± 2.3 to -58.7 ± 2.1 mV (n = 16, P = 0.001). CONCLUSIONS Isoflurane at clinically relevant concentrations inhibits both transient and persistent sodium currents in hippocampal cornu ammonis pyramidal neurons. These mechanisms may contribute to reductions in both hippocampal neuron excitability and synaptic neurotransmission.
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Pan Y, Cummins TR. Distinct functional alterations in SCN8A epilepsy mutant channels. J Physiol 2020; 598:381-401. [PMID: 31715021 PMCID: PMC7216308 DOI: 10.1113/jp278952] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 11/12/2019] [Indexed: 01/12/2023] Open
Abstract
KEY POINTS Mutations in the SCN8A gene cause early infantile epileptic encephalopathy. We characterize a new epilepsy-related SCN8A mutation, R850Q, in the human SCN8A channel and present gain-of-function properties of the mutant channel. Systematic comparison of R850Q with three other SCN8A epilepsy mutations, T761I, R1617Q and R1872Q, identifies one common dysfunction in resurgent current, although these mutations alter distinct properties of the channel. Computational simulations in two different neuron models predict an increased excitability of neurons carrying these mutations, which explains the over-excitation that underlies seizure activities in patients. These data provide further insight into the mechanism of SCN8A-related epilepsy and reveal subtle but potentially important distinction of functional characterization performed in the human vs. rodent channels. ABSTRACT SCN8A is a novel causal gene for early infantile epileptic encephalopathy. It is well accepted that gain-of-function mutations in SCN8A underlie the disorder, although the remarkable heterogeneity of its clinical presentation and poor treatment response demand a better understanding of the disease mechanisms. Here, we characterize a new epilepsy-related SCN8A mutation, R850Q, in human Nav1.6. We show that it is a gain-of-function mutation, with a hyperpolarizing shift in voltage dependence of activation, a two-fold increase of persistent current and a slowed decay of resurgent current. We systematically compare its biophysics with three other SCN8A epilepsy mutations, T767I, R1617Q and R1872Q, in the human Nav1.6 channel. Although all of these mutations are gain-of-function, the mutations affect different aspects of channel properties. One commonality that we discovered is an alteration of resurgent current kinetics, although the mechanisms by which resurgent currents are augmented remain unclear for all of the mutations. Computational simulations predict an increased excitability of neurons carrying these mutations with differential enhancement by open channel blockade.
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Affiliation(s)
- Yanling Pan
- Program in Medical Neuroscience, Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, IN, USA
| | - Theodore R Cummins
- Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, IN, USA
- Department of Biology, School of Science, IUPUI, IN, USA
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Ou M, Zhao W, Liu J, Liang P, Huang H, Yu H, Zhu T, Zhou C. The General Anesthetic Isoflurane Bilaterally Modulates Neuronal Excitability. iScience 2019; 23:100760. [PMID: 31926429 PMCID: PMC6956953 DOI: 10.1016/j.isci.2019.100760] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 11/16/2019] [Accepted: 12/06/2019] [Indexed: 02/05/2023] Open
Abstract
Volatile anesthetics induce hyperactivity during induction while producing anesthesia at higher concentrations. They also bidirectionally modulate many neuronal functions. However, the neuronal mechanism is unclear. The effects of isoflurane on sodium channel currents were analyzed in acute mouse brain slices, including sodium leak (NALCN) currents and voltage-gated sodium channels (Nav) currents. Isoflurane at sub-anesthetic concentrations increased the spontaneous firing rate of CA3 pyramidal neurons, whereas anesthetic concentrations of isoflurane decreased the firing rate. Isoflurane at sub-anesthetic concentrations enhanced NALCN conductance but minimally inhibited Nav currents. Isoflurane at anesthetic concentrations depressed Nav currents and action potential amplitudes. Isoflurane at sub-anesthetic concentrations depolarized resting membrane potential (RMP) of neurons, whereas hyperpolarized the RMP at anesthetic concentrations. Isoflurane at low concentrations induced hyperactivity in vivo, which was diminished in NALCN knockdown mice. In conclusion, enhancement of NALCN by isoflurane contributes to its bidirectional modulation of neuronal excitability and the hyperactivity during induction. Volatile anesthetic isoflurane exerts bidirectional modulation of neuronal excitability Isoflurane enhances NALCN conductance at sub-anesthetic concentration NALCN knockdown diminishes behavioral hyperactivity during isoflurane induction
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Affiliation(s)
- Mengchan Ou
- Laboratory of Anesthesia & Critical Care Medicine, Translational Neuroscience Center, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China; Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Wenling Zhao
- Laboratory of Anesthesia & Critical Care Medicine, Translational Neuroscience Center, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China; Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Jin Liu
- Laboratory of Anesthesia & Critical Care Medicine, Translational Neuroscience Center, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China; Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Peng Liang
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Han Huang
- Department of Anesthesiology, West China Second Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Hai Yu
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Tao Zhu
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China
| | - Cheng Zhou
- Laboratory of Anesthesia & Critical Care Medicine, Translational Neuroscience Center, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China; Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu 610041, Sichuan, P.R. China.
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White HV, Brown ST, Bozza TC, Raman IM. Effects of FGF14 and Na Vβ4 deletion on transient and resurgent Na current in cerebellar Purkinje neurons. J Gen Physiol 2019; 151:1300-1318. [PMID: 31558566 PMCID: PMC6829560 DOI: 10.1085/jgp.201912390] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 09/03/2019] [Indexed: 11/20/2022] Open
Abstract
Voltage-gated Na channels of Purkinje cells are specialized to maintain high availability during high-frequency repetitive firing. They enter fast-inactivated states relatively slowly and undergo a voltage-dependent open-channel block by an intracellular protein (or proteins) that prevents stable fast inactivation and generates resurgent Na current. These properties depend on the pore-forming α subunits, as well as modulatory subunits within the Na channel complex. The identity of the factors responsible for open-channel block remains a question. Here we investigate the effects of genetic mutation of two Na channel auxiliary subunits highly expressed in Purkinje cells, NaVβ4 and FGF14, on modulating Na channel blocked as well as inactivated states. We find that although both NaVβ4 and the FGF14 splice variant FGF14-1a contain sequences that can generate resurgent-like currents when applied to Na channels in peptide form, deletion of either protein, or both proteins simultaneously, does not eliminate resurgent current in acutely dissociated Purkinje cell bodies. Loss of FGF14 expression does, however, reduce resurgent current amplitude and leads to an acceleration and stabilization of inactivation that is not reversed by application of the site-3 toxin, anemone toxin II (ATX). Tetrodotoxin (TTX) sensitivity is higher for resurgent than transient components of Na current, and loss of FGF14 preferentially affects a highly TTX-sensitive subset of Purkinje α subunits. The data suggest that NaV1.6 channels, which are known to generate the majority of Purkinje cell resurgent current, bind TTX with high affinity and are modulated by FGF14 to facilitate open-channel block.
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Affiliation(s)
- Hayley V White
- Department of Neurobiology, Northwestern University, Evanston, IL.,Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL
| | - Spencer T Brown
- Department of Neurobiology, Northwestern University, Evanston, IL.,Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL
| | - Thomas C Bozza
- Department of Neurobiology, Northwestern University, Evanston, IL.,Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL
| | - Indira M Raman
- Department of Neurobiology, Northwestern University, Evanston, IL .,Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL
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Ciotu CI, Tsantoulas C, Meents J, Lampert A, McMahon SB, Ludwig A, Fischer MJM. Noncanonical Ion Channel Behaviour in Pain. Int J Mol Sci 2019; 20:E4572. [PMID: 31540178 PMCID: PMC6770626 DOI: 10.3390/ijms20184572] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 09/09/2019] [Accepted: 09/12/2019] [Indexed: 12/19/2022] Open
Abstract
Ion channels contribute fundamental properties to cell membranes. Although highly diverse in conductivity, structure, location, and function, many of them can be regulated by common mechanisms, such as voltage or (de-)phosphorylation. Primarily considering ion channels involved in the nociceptive system, this review covers more novel and less known features. Accordingly, we outline noncanonical operation of voltage-gated sodium, potassium, transient receptor potential (TRP), and hyperpolarization-activated cyclic nucleotide (HCN)-gated channels. Noncanonical features discussed include properties as a memory for prior voltage and chemical exposure, alternative ion conduction pathways, cluster formation, and silent subunits. Complementary to this main focus, the intention is also to transfer knowledge between fields, which become inevitably more separate due to their size.
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Affiliation(s)
- Cosmin I Ciotu
- Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria
| | | | - Jannis Meents
- Institute of Physiology, University Hospital RWTH Aachen, 52074 Aachen, Germany
| | - Angelika Lampert
- Institute of Physiology, University Hospital RWTH Aachen, 52074 Aachen, Germany
| | - Stephen B McMahon
- Wolfson Centre for Age-Related Diseases, King's College London, London SE1 1UR, UK
| | - Andreas Ludwig
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
| | - Michael J M Fischer
- Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria.
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