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Stephen G Waxman - One of the best experts on this subject based on the ideXlab platform.
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status of peripheral sodium channel blockers for non addictive pain treatment
Nature Reviews Neurology, 2020Co-Authors: Matthew Alsaloum, Grant P. Higerd, Philip R. Effraim, Stephen G WaxmanAbstract:The effective and safe treatment of pain is an unmet health-care need. Current medications used for pain management are often only partially effective, carry dose-limiting adverse effects and are potentially addictive, highlighting the need for improved therapeutic agents. Most common pain conditions originate in the periphery, where dorsal root ganglion and trigeminal ganglion neurons feed pain information into the CNS. Voltage-gated sodium (NaV) channels drive neuronal excitability and three subtypes - NaV1.7, NaV1.8 and NaV1.9 - are preferentially expressed in the peripheral nervous system, suggesting that their inhibition might treat pain while avoiding central and cardiac adverse effects. Genetic and functional studies of human pain disorders have identified NaV1.7, NaV1.8 and NaV1.9 as mediators of pain and validated them as targets for pain treatment. Consequently, multiple NaV1.7-specific and NaV1.8-specific blockers have undergone clinical trials, with others in preclinical development, and the targeting of NaV1.9, although hampered by technical constraints, might also be moving ahead. In this Review, we summarize the clinical and preclinical literature describing compounds that target peripheral NaV channels and discuss the challenges and future prospects for the field. Although the potential of peripheral NaV channel inhibition for the treatment of pain has yet to be realized, this remains a promising strategy to achieve non-addictive analgesia for multiple pain conditions.
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Nav1.9 expression in magnocellular neurosecretory cells of supraoptic nucleus
Experimental Neurology, 2014Co-Authors: Joel A Black, Dymtro Vasylyev, Sulayman D Dib-hajj, Stephen G WaxmanAbstract:Abstract Osmoregulation in mammals is tightly controlled by the release of vasopressin and oxytocin from magnocellular neurosecretory cells (MSC) of the supraoptic nucleus (SON). The release of vasopressin and oxytocin in the neurohypophysis by axons of MSC is regulated by bursting activity of these neurons, which is influenced by multiple sources, including intrinsic membrane properties, paracrine contributions of glial cells, and extrinsic synaptic inputs. Previous work has shown that bursting activity of MSC is tetrodotoxin (TTX)-sensitive, and that TTX-S sodium channels Nav1.2, Nav1.6 and Nav1.7 are expressed by MSC and upregulated in response to osmotic challenge in rats. The TTX-resistant sodium channels, NaV1.8 and Nav1.9, are preferentially expressed, at relatively high levels, in peripheral neurons, where their properties are linked to repetitive firing and subthreshold electrogenesis, respectively, and are often referred to as “peripheral” sodium channels. Both sodium channels have been implicated in pain pathways, and are under study as potential therapeutic targets for pain medications which might be expected to have minimal CNS side effects. We show here, however, that Nav1.9 is expressed by vasopressin- and oxytocin-producing MSC of the rat supraoptic nucleus (SON). We also show that cultured MSC exhibit sodium currents that have characteristics of Nav1.9 channels. In contrast, Nav1.8 is not detectable in the SON. These results suggest that Nav1.9 may contribute to the firing pattern of MSC of the SON, and that careful assessment of hypothalamic function be performed as NaV1.9 blocking agents are studied as potential pain therapies.
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nav1 7 stress induced changes in immunoreactivity within magnocellular neurosecretory neurons of the supraoptic nucleus
Molecular Pain, 2013Co-Authors: Joel A Black, Janneke G J Hoeijmakers, Catharina G Faber, Ingemar S J Merkies, Stephen G WaxmanAbstract:Background: NaV1.7 is preferentially expressed, at relatively high levels, in peripheral neurons, and is often referred to as a “peripheral” sodium channel, and NaV1.7-specific blockers are under study as potential pain therapeutics which might be expected to have minimal CNS side effects. However, occasional reports of patients with NaV1.7 gain-of-function mutations and apparent hypothalamic dysfunction have appeared. The two sodium channels previously studied within the rat hypothalamic supraoptic nucleus, NaV1.2 and NaV1.6, display up-regulated expression in response to osmotic stress. Results: Here we show that NaV1.7 is present within vasopressin-producing neurons and oxytocin-producing neurons within the rat hypothalamus, and demonstrate that the level of Nav1.7 immunoreactivity is increased in these cells in response to osmotic stress. Conclusions: NaV1.7 is present within neurosecretory neurons of rat supraoptic nucleus, where the level of immunoreactivity is dynamic, increasing in response to osmotic stress. Whether NaV1.7 levels are up-regulated within the human hypothalamus in response to environmental factors or stress, and whether NaV1.7 plays a functional role in human hypothalamus, is not yet known. Until these questions are resolved, the present findings suggest the need for careful assessment of hypothalamic function in patients with NaV1.7 mutations, especially when subjected to stress, and for monitoring of hypothalamic function as NaV1.7 blocking agents are studied.
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a sodium channel mutation linked to epilepsy increases ramp and persistent current of nav1 3 and induces hyperexcitability in hippocampal neurons
Experimental Neurology, 2010Co-Authors: Mark Estacion, Andreas Gasser, Sulayman D Dibhajj, Stephen G WaxmanAbstract:article i nfo Voltage-gated sodium channelopathies underlie many excitability disorders. Genes SCN1A, SCN2A and SCN9A, which encode pore-forming α-subunits NaV1.1, NaV1.2 and NaV1.7, are clustered on human chromosome 2, and mutations in these genes have been shown to underlie epilepsy, migraine, and somatic pain disorders. SCN3A, the gene which encodes NaV1.3, is part of this cluster, but until recently was not associated with any mutation. A charge-neutralizing mutation, K345Q, in the NaV1.3 DI/S5-6 linker has recently been identified in a patient with cryptogenic partial epilepsy. Pathogenicity of the NaV1.3/K354Q mutation has been inferred from the conservation of this residue in all sodium channels and its absence from control alleles, but functional analysis has been limited to the corresponding substitution in the cardiac muscle sodium channel NaV1.5. Since identical mutations may produce different effects within different sodium channel isoforms, we assessed the K354Q mutation within its native NaV1.3 channel and studied the effect of the mutant NaV1.3/K354Q channels on hippocampal neuron excitability. We show here that the K354Q mutation enhances the persistent and ramp currents of NaV1.3, reduces current threshold and produces spontaneous firing and paroxysmal depolarizing shift-like complexes in hippocampal neurons. Our data provide a pathophysiological basis for the pathogenicity of the first epilepsy-linked mutation within NaV1.3 channels and hippocampal neurons.
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A sodium channel mutation linked to epilepsy increases ramp and persistent current of Nav1.3 and induces hyperexcitability in hippocampal neurons
Experimental Neurology, 2010Co-Authors: Mark Estacion, Andreas Gasser, Sulayman D Dib-hajj, Stephen G WaxmanAbstract:Abstract Voltage-gated sodium channelopathies underlie many excitability disorders. Genes SCN1A, SCN2A and SCN9A, which encode pore-forming α-subunits NaV1.1, NaV1.2 and NaV1.7, are clustered on human chromosome 2, and mutations in these genes have been shown to underlie epilepsy, migraine, and somatic pain disorders. SCN3A, the gene which encodes NaV1.3, is part of this cluster, but until recently was not associated with any mutation. A charge-neutralizing mutation, K345Q, in the NaV1.3 DI/S5-6 linker has recently been identified in a patient with cryptogenic partial epilepsy. Pathogenicity of the NaV1.3/K354Q mutation has been inferred from the conservation of this residue in all sodium channels and its absence from control alleles, but functional analysis has been limited to the corresponding substitution in the cardiac muscle sodium channel NaV1.5. Since identical mutations may produce different effects within different sodium channel isoforms, we assessed the K354Q mutation within its native NaV1.3 channel and studied the effect of the mutant NaV1.3/K354Q channels on hippocampal neuron excitability. We show here that the K354Q mutation enhances the persistent and ramp currents of NaV1.3, reduces current threshold and produces spontaneous firing and paroxysmal depolarizing shift-like complexes in hippocampal neurons. Our data provide a pathophysiological basis for the pathogenicity of the first epilepsy-linked mutation within NaV1.3 channels and hippocampal neurons.
Jan Tytgat - One of the best experts on this subject based on the ideXlab platform.
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Differential effects of the recombinant toxin PnTx4(5-5) from the spider Phoneutria nigriventer on mammalian and insect sodium channels
Biochimie, 2015Co-Authors: Ana Luiza B. Paiva, Alessandra Matavel, Marta N. Cordeiro, Marcelo R.v. Diniz, Steve Peigneur, Jan Tytgat, Maria Elena De LimaAbstract:Abstract The toxin PnTx4(5-5) from the spider Phoneutria nigriventer is extremely toxic/lethal to insects but has no macroscopic behavioral effects observed in mice after intracerebral injection. Nevertheless, it was demonstrated that it inhibits the N-methyl- d -aspartate (NMDA) - subtype of glutamate receptors of cultured rat hippocampal neurons. PnTx4(5-5) has 63% identity to PnTx4(6-1), another insecticidal toxin from P. nigriventer, which can slow down the sodium current inactivation in insect central nervous system, but has no effect on Nav1.2 and Nav1.4 rat sodium channels. Here, we have cloned and heterologous expressed the toxin PnTx4(5-5) in Escherichia coli. The recombinant toxin rPnTx4(5-5) was tested on the sodium channel NavBg from the cockroach Blatella germanica and on mammalian sodium channels Nav1.2-1.6, all expressed in Xenopus leavis oocytes. We showed that the toxin has different affinity and mode of action on insect and mammalian sodium channels. The most remarkable effect was on NavBg, where rPnTx4(5-5) strongly slowed down channel inactivation (EC50 = 212.5 nM), and at 1 μM caused an increase on current peak amplitude of 105.2 ± 3.1%. Interestingly, the toxin also inhibited sodium current on all the mammalian channels tested, with the higher current inhibition on Nav1.3 (38.43 ± 8.04%, IC50 = 1.5 μM). Analysis of activation curves on Nav1.3 and Nav1.5 showed that the toxin shifts channel activation to more depolarized potentials, which can explain the sodium current inhibition. Furthermore, the toxin also slightly slowed down sodium inactivation on Nav1.3 and Nav1.6 channels. As far as we know, this is the first araneomorph toxin described which can shift the sodium channel activation to more depolarized potentials and also slows down channel inactivation.
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Electrophysiological characterization of the first Tityus serrulatus alpha-like toxin, Ts5: Evidence of a pro-inflammatory toxin on macrophages
Biochimie, 2015Co-Authors: Manuela Berto Pucca, Felipe A. Cerni, Karina Furlan Zoccal, Karla De Castro Figueiredo Bordon, Camila Takeno Cologna, Steve Peigneur, Lúcia Helena Faccioli, Jan Tytgat, Eliane Candiani ArantesAbstract:Abstract Tityus serrulatus (Ts) venom is composed of mainly neurotoxins specific for voltage-gated K+ and Na+ channels, which are expressed in many cells such as macrophages. Macrophages are the first line of defense invasion and they participate in the inflammatory response of Ts envenoming. However, little is known about the effect of Ts toxins on macrophage activation. This study investigated the effect of Ts5 toxin on different sodium channels as well as its role on the macrophage immunomodulation. The electrophysiological assays showed that Ts5 inhibits the rapid inactivation of the mammalian sodium channels Nav1.2, Nav1.3, Nav1.4, Nav1.5, Nav1.6 and Nav1.7. Interestingly, Ts5 also inhibits the inactivation of the insect Drosophila melanogaster sodium channel (DmNav1), and it is therefore classified as the first Ts α-like toxin. The immunological experiments on macrophages reveal that Ts5 is a pro-inflammatory toxin inducing the cytokine production of tumor necrosis factor (TNF)-α and interleukin (IL)-6. On the basis of recent literature, our study also stresses a possible mechanism responsible for venom-associated molecular patterns (VAMPs) internalization and macrophage activation and moreover we suggest two main pathways of VAMPs signaling: direct and indirect. This work provides useful insights for a better understanding of the involvement of VAMPs in macrophage modulation.
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Evolutionary Diversification of Mesobuthus α-Scorpion Toxins Affecting Sodium Channels
Molecular & Cellular Proteomics, 2011Co-Authors: Steve Peigneur, Xiuxiu Lu, Jan TytgatAbstract:α-Scorpion toxins constitute a family of peptide modulators that induce a prolongation of the action potential of excitable cells by inhibiting voltage-gated sodium channel inactivation. Although they all adopt a conserved structural scaffold, the potency and phylogentic preference of these toxins largely vary, which render them an intriguing model for studying evolutionary diversification among family members. Here, we report molecular characterization of a new multigene family of α-toxins comprising 13 members (named MeuNaTxα-1 to MeuNaTxα-13) from the scorpion Mesobuthus eupeus. Of them, five native toxins (MeuNaTxα-1 to -5) were purified to homogeneity from the venom and the solution structure of MeuNaTxα-5 was solved by nuclear magnetic resonance. A systematic functional evaluation of MeuNaTxα-1, -2, -4, and -5 was conducted by two-electrode voltage-clamp recordings on seven cloned mammalian voltage-gated sodium channels (Nav1.2 to Nav1.8) and the insect counterpart DmNav1 expressed in Xenopus oocytes. Results show that all these four peptides slow inactivation of DmNav1 and are inactive on Nav1.8 at micromolar concentrations. However, they exhibit differential specificity for the other six channel isoforms (Nav1.2 to Nav1.7), in which MeuNaTxα-4 shows no activity on these isoforms and thus represents the first Mesobuthus-derived insect-selective α-toxin identified so far with a half maximal effective concentration of 130 ± 2 nm on DmNav1 and a half maximal lethal dose of about 200 pmol g−1 on the insect Musca domestica; MeuNaTxα-2 only affects Nav1.4; MeuNaTxα-1 and MeuNaTxα-5 have a wider range of channel spectrum, the former active on Nav1.2, Nav1.3, Nav1.6, and Nav1.7, whereas the latter acting on Nav1.3–Nav1.7. Remarkably, MeuNaTxα-4 and MeuNaTxα-5 are two nearly identical peptides differing by only one point mutation at site 50 (A50V) but exhibit rather different channel subtype selectivity, highlighting a switch role of this site in altering the target specificity. By the maximum likelihood models of codon substitution, we detected nine positively selected sites (PSSs) that could be involved in functional diversification of Mesobuthus α-toxins. The PSSs include site 50 and other seven sites located in functional surfaces of α-toxins. This work represents the first thorough investigation of evolutionary diversification of α-toxins derived from a specific scorpion lineage from the perspectives of sequence, structure, function, and evolution.
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potent modulation of the voltage gated sodium channel nav1 7 by od1 a toxin from the scorpion odonthobuthus doriae
Molecular Pharmacology, 2006Co-Authors: Chantal Maertens, Eva Cuypers, Mehriar Amininasab, Amir Jalali, Hossein Vatanpour, Jan TytgatAbstract:Voltage-gated sodium channels are essential for the propagation of action potentials in nociceptive neurons. Nav1.7 is found in peripheral sensory and sympathetic neurons and involved in short-term and inflammatory pain. Nav1.8 and Nav1.3 are major players in nociception and neuropathic pain, respectively. In our effort to identify isoform-specific and high-affinity ligands for these channels, we investigated the effects of OD1, a scorpion toxin isolated from the venom of the scorpion Odonthobuthus doriae. Nav1.3, Nav1.7, and Nav1.8 channels were coexpressed with beta1-subunits in Xenopus laevis oocytes. Na+ currents were recorded with the two-electrode voltage-clamp technique. OD1 modulates Nav1.7 at low nanomolar concentrations: 1) fast inactivation is dramatically impaired, with an EC50 value of 4.5 nM; 2) OD1 substantially increases the peak current at all voltages; and 3) OD1 induces a substantial persistent current. Nav1.8 was not affected by concentrations up to 2 microM, whereas Nav1.3 was sensitive only to concentrations higher than 100 nM. OD1 impairs the inactivation process of Nav1.3 with an EC50 value of 1127 nM. Finally, the effects of OD1 were compared with a classic alpha-toxin, AahII from Androctonus australis Hector and a classic alpha-like toxin, BmK M1 from Buthus martensii Karsch. At a concentration of 50 nM, both toxins affected Nav1.7. Nav1.3 was sensitive to AahII but not to BmK M1, whereas Nav1.8 was affected by neither toxin. In conclusion, the present study shows that the scorpion toxin OD1 is a potent modulator of Nav1.7, with a unique selectivity pattern.
Takeyoshi Sata - One of the best experts on this subject based on the ideXlab platform.
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Antidepressants inhibit Nav1.3, Nav1.7, and Nav1.8 neuronal voltage-gated sodium channels more potently than Nav1.2 and Nav1.6 channels expressed in Xenopus oocytes.
Naunyn-schmiedebergs Archives of Pharmacology, 2017Co-Authors: Takafumi Horishita, Dan Okura, Yasuhito Uezono, Susumu Ueno, Yuichi Ogata, Reiko Horishita, Tomoko Minami, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:Tricyclic antidepressants (TCAs) and duloxetine are used to treat neuropathic pain. However, the mechanisms underlying their analgesic effects remain unclear. Although many investigators have shown inhibitory effects of antidepressants on voltage-gated sodium channels (Nav) as a possible mechanism of analgesia, to our knowledge, no one has compared effects on the diverse variety of sodium channel α subunits. We investigated the effects of antidepressants on sodium currents in Xenopus oocytes expressing Nav1.2, Nav1.3, Nav1.6, Nav1.7, and Nav1.8 with a β1 subunit by using whole-cell, two-electrode, voltage clamp techniques. We also studied the role of the β3 subunit on the effect of antidepressants on Nav1.3. All antidepressants inhibited sodium currents in an inactivated state induced by all five α subunits with β1. The inhibitory effects were more potent for Nav1.3, Nav1.7, and Nav1.8, which are distributed in dorsal root ganglia, than Nav1.2 and Nav1.6, which are distributed primarily in the central nervous system. The effect of amitriptyline on Nav1.7 with β1 was most potent with a half-maximal inhibitory concentration (IC50) 4.6 μmol/L. IC50 for amitriptyline on Nav1.3 coexpressed with β1 was lowered from 8.4 to 4.5 μmol/L by coexpression with β3. Antidepressants predominantly inhibited the sodium channels expressed in dorsal root ganglia, and amitriptyline has the most potent inhibitory effect. This is the first evidence, to our knowledge, showing the diverse effects of antidepressants on various α subunits. Moreover, the β3 subunit appears important for inhibition of Nav1.3. These findings may aid better understanding of the mechanisms underlying the pain relieving effects of antidepressants.
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Neurosteroids allopregnanolone sulfate and pregnanolone sulfate have diverse effect on the α subunit of the neuronal voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 expressed in xenopus oocytes.
Anesthesiology, 2014Co-Authors: Takafumi Horishita, Dan Okura, Yasuhito Uezono, Susumu Ueno, Tomoko Minami, Takashi Kawasaki, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:BACKGROUND: The neurosteroids allopregnanolone and pregnanolone are potent positive modulators of γ-aminobutyric acid type A receptors. Antinociceptive effects of allopregnanolone have attracted much attention because recent reports have indicated the potential of allopregnanolone as a therapeutic agent for refractory pain. However, the analgesic mechanisms of allopregnanolone are still unclear. Voltage-gated sodium channels (Nav) are thought to play important roles in inflammatory and neuropathic pain, but there have been few investigations on the effects of allopregnanolone on sodium channels. METHODS: Using voltage-clamp techniques, the effects of allopregnanolone sulfate (APAS) and pregnanolone sulfate (PAS) on sodium current were examined in Xenopus oocytes expressing Nav1.2, Nav1.6, Nav1.7, and Nav1.8 α subunits. RESULTS: APAS suppressed sodium currents of Nav1.2, Nav1.6, and Nav1.7 at a holding potential causing half-maximal current in a concentration-dependent manner, whereas it markedly enhanced sodium current of Nav1.8 at a holding potential causing maximal current. Half-maximal inhibitory concentration values for Nav1.2, Nav1.6, and Nav1.7 were 12 ± 4 (n = 6), 41 ± 2 (n = 7), and 131 ± 15 (n = 5) μmol/l (mean ± SEM), respectively. The effects of PAS were lower than those of APAS. From gating analysis, two compounds increased inactivation of all α subunits, while they showed different actions on activation of each α subunit. Moreover, two compounds showed a use-dependent block on Nav1.2, Nav1.6, and Nav1.7. CONCLUSION: APAS and PAS have diverse effects on sodium currents in oocytes expressing four α subunits. APAS inhibited the sodium currents of Nav1.2 most strongly.
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The endocannabinoid anandamide inhibits voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 in Xenopus oocytes.
Anesthesia & Analgesia, 2014Co-Authors: Dan Okura, Takafumi Horishita, Yasuhito Uezono, Susumu Ueno, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:BACKGROUND:Anandamide is an endocannabinoid that regulates multiple physiological functions by pharmacological actions, in a manner similar to marijuana. Recently, much attention has been paid to the analgesic effect of endocannabinoids in terms of identifying new pharmacotherapies for refractory pa
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The endocannabinoid anandamide inhibits voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 in Xenopus oocytes.
Anesthesia & Analgesia, 2014Co-Authors: Dan Okura, Takafumi Horishita, Yasuhito Uezono, Susumu Ueno, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:BACKGROUND: Anandamide is an endocannabinoid that regulates multiple physiological functions by pharmacological actions, in a manner similar to marijuana. Recently, much attention has been paid to the analgesic effect of endocannabinoids in terms of identifying new pharmacotherapies for refractory pain management, but the mechanisms of the analgesic effects of anandamide are still obscure. Voltage-gated sodium channels are believed to play important roles in inflammatory and neuropathic pain. We investigated the effects of anandamide on 4 neuronal sodium channel α subunits, Nav1.2, Nav1.6, Nav1.7, and Nav1.8, to explore the mechanisms underlying the antinociceptive effects of anandamide. METHODS: We studied the effects of anandamide on Nav1.2, Nav1.6, Nav1.7, and Nav1.8 α subunits with β1 subunits by using whole-cell, 2-electrode, voltage-clamp techniques in Xenopus oocytes. RESULTS: Anandamide inhibited sodium currents of all subunits at a holding potential causing half-maximal current (V1/2) in a concentration-dependent manner. The half-maximal inhibitory concentration values for Nav1.2, Nav1.6, Nav1.7, and Nav1.8 were 17, 12, 27, and 40 μmol/L, respectively, indicating an inhibitory effect on Nav1.6, which showed the highest potency. Anandamide raised the depolarizing shift of the activation curve as well as the hyperpolarizing shift of the inactivation curve in all α subunits, suggesting that sodium current inhibition was due to decreased activation and increased inactivation. Moreover, anandamide showed a use-dependent block in Nav1.2, Nav1.6, and Nav1.7 but not Nav1.8. CONCLUSION: Anandamide inhibited the function of α subunits in neuronal sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8. These results help clarify the mechanisms of the analgesic effects of anandamide.
Takafumi Horishita - One of the best experts on this subject based on the ideXlab platform.
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Antidepressants inhibit Nav1.3, Nav1.7, and Nav1.8 neuronal voltage-gated sodium channels more potently than Nav1.2 and Nav1.6 channels expressed in Xenopus oocytes.
Naunyn-schmiedebergs Archives of Pharmacology, 2017Co-Authors: Takafumi Horishita, Dan Okura, Yasuhito Uezono, Susumu Ueno, Yuichi Ogata, Reiko Horishita, Tomoko Minami, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:Tricyclic antidepressants (TCAs) and duloxetine are used to treat neuropathic pain. However, the mechanisms underlying their analgesic effects remain unclear. Although many investigators have shown inhibitory effects of antidepressants on voltage-gated sodium channels (Nav) as a possible mechanism of analgesia, to our knowledge, no one has compared effects on the diverse variety of sodium channel α subunits. We investigated the effects of antidepressants on sodium currents in Xenopus oocytes expressing Nav1.2, Nav1.3, Nav1.6, Nav1.7, and Nav1.8 with a β1 subunit by using whole-cell, two-electrode, voltage clamp techniques. We also studied the role of the β3 subunit on the effect of antidepressants on Nav1.3. All antidepressants inhibited sodium currents in an inactivated state induced by all five α subunits with β1. The inhibitory effects were more potent for Nav1.3, Nav1.7, and Nav1.8, which are distributed in dorsal root ganglia, than Nav1.2 and Nav1.6, which are distributed primarily in the central nervous system. The effect of amitriptyline on Nav1.7 with β1 was most potent with a half-maximal inhibitory concentration (IC50) 4.6 μmol/L. IC50 for amitriptyline on Nav1.3 coexpressed with β1 was lowered from 8.4 to 4.5 μmol/L by coexpression with β3. Antidepressants predominantly inhibited the sodium channels expressed in dorsal root ganglia, and amitriptyline has the most potent inhibitory effect. This is the first evidence, to our knowledge, showing the diverse effects of antidepressants on various α subunits. Moreover, the β3 subunit appears important for inhibition of Nav1.3. These findings may aid better understanding of the mechanisms underlying the pain relieving effects of antidepressants.
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Neurosteroids allopregnanolone sulfate and pregnanolone sulfate have diverse effect on the α subunit of the neuronal voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 expressed in xenopus oocytes.
Anesthesiology, 2014Co-Authors: Takafumi Horishita, Dan Okura, Yasuhito Uezono, Susumu Ueno, Tomoko Minami, Takashi Kawasaki, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:BACKGROUND: The neurosteroids allopregnanolone and pregnanolone are potent positive modulators of γ-aminobutyric acid type A receptors. Antinociceptive effects of allopregnanolone have attracted much attention because recent reports have indicated the potential of allopregnanolone as a therapeutic agent for refractory pain. However, the analgesic mechanisms of allopregnanolone are still unclear. Voltage-gated sodium channels (Nav) are thought to play important roles in inflammatory and neuropathic pain, but there have been few investigations on the effects of allopregnanolone on sodium channels. METHODS: Using voltage-clamp techniques, the effects of allopregnanolone sulfate (APAS) and pregnanolone sulfate (PAS) on sodium current were examined in Xenopus oocytes expressing Nav1.2, Nav1.6, Nav1.7, and Nav1.8 α subunits. RESULTS: APAS suppressed sodium currents of Nav1.2, Nav1.6, and Nav1.7 at a holding potential causing half-maximal current in a concentration-dependent manner, whereas it markedly enhanced sodium current of Nav1.8 at a holding potential causing maximal current. Half-maximal inhibitory concentration values for Nav1.2, Nav1.6, and Nav1.7 were 12 ± 4 (n = 6), 41 ± 2 (n = 7), and 131 ± 15 (n = 5) μmol/l (mean ± SEM), respectively. The effects of PAS were lower than those of APAS. From gating analysis, two compounds increased inactivation of all α subunits, while they showed different actions on activation of each α subunit. Moreover, two compounds showed a use-dependent block on Nav1.2, Nav1.6, and Nav1.7. CONCLUSION: APAS and PAS have diverse effects on sodium currents in oocytes expressing four α subunits. APAS inhibited the sodium currents of Nav1.2 most strongly.
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The endocannabinoid anandamide inhibits voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 in Xenopus oocytes.
Anesthesia & Analgesia, 2014Co-Authors: Dan Okura, Takafumi Horishita, Yasuhito Uezono, Susumu Ueno, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:BACKGROUND:Anandamide is an endocannabinoid that regulates multiple physiological functions by pharmacological actions, in a manner similar to marijuana. Recently, much attention has been paid to the analgesic effect of endocannabinoids in terms of identifying new pharmacotherapies for refractory pa
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The endocannabinoid anandamide inhibits voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 in Xenopus oocytes.
Anesthesia & Analgesia, 2014Co-Authors: Dan Okura, Takafumi Horishita, Yasuhito Uezono, Susumu Ueno, Nobuyuki Yanagihara, Yuka Sudo, Takeyoshi SataAbstract:BACKGROUND: Anandamide is an endocannabinoid that regulates multiple physiological functions by pharmacological actions, in a manner similar to marijuana. Recently, much attention has been paid to the analgesic effect of endocannabinoids in terms of identifying new pharmacotherapies for refractory pain management, but the mechanisms of the analgesic effects of anandamide are still obscure. Voltage-gated sodium channels are believed to play important roles in inflammatory and neuropathic pain. We investigated the effects of anandamide on 4 neuronal sodium channel α subunits, Nav1.2, Nav1.6, Nav1.7, and Nav1.8, to explore the mechanisms underlying the antinociceptive effects of anandamide. METHODS: We studied the effects of anandamide on Nav1.2, Nav1.6, Nav1.7, and Nav1.8 α subunits with β1 subunits by using whole-cell, 2-electrode, voltage-clamp techniques in Xenopus oocytes. RESULTS: Anandamide inhibited sodium currents of all subunits at a holding potential causing half-maximal current (V1/2) in a concentration-dependent manner. The half-maximal inhibitory concentration values for Nav1.2, Nav1.6, Nav1.7, and Nav1.8 were 17, 12, 27, and 40 μmol/L, respectively, indicating an inhibitory effect on Nav1.6, which showed the highest potency. Anandamide raised the depolarizing shift of the activation curve as well as the hyperpolarizing shift of the inactivation curve in all α subunits, suggesting that sodium current inhibition was due to decreased activation and increased inactivation. Moreover, anandamide showed a use-dependent block in Nav1.2, Nav1.6, and Nav1.7 but not Nav1.8. CONCLUSION: Anandamide inhibited the function of α subunits in neuronal sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8. These results help clarify the mechanisms of the analgesic effects of anandamide.
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n-alcohols inhibit voltage-gated Na+ channels expressed in Xenopus oocytes
Journal of Pharmacology and Experimental Therapeutics, 2008Co-Authors: Takafumi Horishita, R. Adron HarrisAbstract:Voltage-gated sodium channels are essential for the initiation and propagation of action potentials in excitable cells and are known as a target of local anesthetics. In addition, inhibition of sodium channels by volatile anesthetics has been proposed as a mechanism of general anesthesia. The n-alcohols produce anesthesia, and their potency increases with carbon number until a “cut-off” is reached. In this study, we examined effects of a range of n-alcohols on Nav1.2 subunits to determine the alcohol cut-off for this channel. We also studied the effect of a short-chain alcohol (ethanol) and a long-chain alcohol (octanol) on Nav1.2, Nav1.4, Nav1.6, and Nav1.8 subunits, and we investigated the effects of alcohol on channel kinetics. Ethanol and octanol inhibited sodium currents of all subunits, and the inhibition of the Nav1.2 channel by n-alcohols indicated a cut-off at nonanol. Ethanol and octanol produced open-channel block, which was more pronounced for Nav1.8 than for the other sodium channels. Inhibition of Nav1.2 was due to decreased activation and increased inactivation. These results suggest that sodium channels may have a hydrophobic binding site for n-alcohols and demonstrate the differences in the kinetic mechanisms of inhibition for n-alcohols and inhaled anesthetics.
Todd Scheuer - One of the best experts on this subject based on the ideXlab platform.
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localization of sodium channel subtypes in mouse ventricular myocytes using quantitative immunocytochemistry
Journal of Molecular and Cellular Cardiology, 2013Co-Authors: Ruth E Westenbroek, Sebastian Bischoff, Sebastian K G Maier, Ying Fu, William A. Catterall, Todd ScheuerAbstract:Voltage-gated sodium channels are responsible for the rising phase of the action potential in cardiac muscle. Previously, both TTX-sensitive neuronal sodium channels (NaV1.1, NaV1.2, NaV1.3, Nav1.4 and NaV1.6) and the TTX-resistant cardiac sodium channel (NaV1.5) have been detected in cardiac myocytes, but relative levels of protein expression of the isoforms were not determined. Using a quantitative approach, we analyzed z-series of confocal microscopy images from individual mouse myocytes stained with either anti-NaV1.1, anti-NaV1.2, anti-NaV1.3, anti-Nav1.4, anti-NaV1.5, or anti-NaV1.6 antibodies and calculated the relative intensity of staining for these sodium channel isoforms. Our results indicate that the TTX-sensitive channels represented approximately 23% of the total channels, whereas the TTX-resistant NaV1.5 channel represented 77% of the total channel staining in mouse ventricular myocytes. These ratios are consistent with previous electrophysiological studies in mouse ventricular myocytes. NaV1.5 was located at the cell surface, with high density at the intercalated disc, but was absent from the transverse (t)-tubular system, suggesting that these channels support surface conduction and inter-myocyte transmission. Low-level cell surface staining of Nav1.4 and NaV1.6 channels suggest a minor role in surface excitation and conduction. Conversely, NaV1.1 and NaV1.3 channels are localized to the t-tubules and are likely to support t-tubular transmission of the action potential to the myocyte interior. This quantitative immunocytochemical approach for assessing sodium channel density and localization provides a more precise view of the relative importance and possible roles of these individual sodium channel protein isoforms in mouse ventricular myocytes and may be applicable to other species and cardiac tissue types.
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molecular determinants for modulation of persistent sodium current by g protein βγ subunits
The Journal of Neuroscience, 2005Co-Authors: Massimo Mantegazza, William A. Catterall, Frank H Yu, Andrew J Powell, Jeffrey J Clare, Todd ScheuerAbstract:Voltage-gated sodium channels are responsible for the upstroke of the action potential in most excitable cells, and their fast inactivation is essential for controlling electrical signaling. In addition, a noninactivating, persistent component of sodium current, I NaP, has been implicated in integrative functions of neurons including threshold for firing, neuronal bursting, and signal integration. G-protein βγ subunits increase I NaP, but the sodium channel subtypes that conduct I NaP and the target site(s) on the sodium channel molecule required for modulation by Gβγ are poorly defined. Here, we show that I NaP conducted by Nav1.1 and Nav1.2 channels (Nav1.1 > Nav1.2) is modulated by Gβγ; Nav1.4 and Nav1.5 channels produce smaller I NaP that is not regulated by Gβγ. These qualitative differences in modulation by Gβγ are determined by the transmembrane body of the sodium channels rather than their cytoplasmic C-terminal domains, which have been implicated previously in modulation by Gβγ. However, the C-terminal domains determine the quantitative extent of modulation of Nav1.2 channels by Gβγ. Studies of chimeric and truncated Nav1.2 channels identify molecular determinants that affect modulation of I NaP located between amino acid residue 1890 and the C terminus at residue 2005. The last 28 amino acid residues of the C terminus are sufficient to support modulation by Gβγ when attached to the proximal C-terminal domain. Our results further define the sodium channel subtypes that generate I NaP and identify crucial molecular determinants in the C-terminal domain required for modulation by Gβγ when attached to the transmembrane body of a responsive sodium channel.
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an unexpected role for brain type sodium channels in coupling of cell surface depolarization to contraction in the heart
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Sebastian K G Maier, Ruth E Westenbroek, Kenneth A Schenkman, Eric O Feigl, Todd Scheuer, William A. CatterallAbstract:Voltage-gated sodium channels composed of pore-forming α and auxiliary β subunits are responsible for the rising phase of the action potential in cardiac muscle, but the functional roles of distinct sodium channel subtypes have not been clearly defined. Immunocytochemical studies show that the principal cardiac pore-forming α subunit isoform Nav1.5 is preferentially localized in intercalated disks, whereas the brain α subunit isoforms Nav1.1, Nav1.3, and Nav1.6 are localized in the transverse tubules. Sodium currents due to the highly tetrodotoxin (TTX)-sensitive brain isoforms in the transverse tubules are small and are detectable only after activation with β scorpion toxin. Nevertheless, they play an important role in coupling depolarization of the cell surface membrane to contraction, because low TTX concentrations reduce left ventricular function. Our results suggest that the principal cardiac isoform in the intercalated disks is primarily responsible for action potential conduction between cells and reveal an unexpected role for brain sodium channel isoforms in the transverse tubules in coupling electrical excitation to contraction in cardiac muscle.
