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Stephen G Waxman - One of the best experts on this subject based on the ideXlab platform.
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lacosamide in patients with Nav1.7 mutations related small fibre neuropathy a randomized controlled trial
Brain, 2019Co-Authors: Bianca T A De Greef, Janneke G J Hoeijmakers, Catharina G Faber, Sulayman D Dibhajj, Stephen G Waxman, Margot Geerts, Mike Oakes, Tim J E Church, Ingemar S J MerkiesAbstract:Symptomatic treatment of neuropathic pain in small fibre neuropathy is often disappointing. The finding of voltage-gated sodium channel mutations in small fibre neuropathy (with mutations in SCN9A, encoding for Nav1.7) being most frequently reported suggest a specific target for therapy. The anticonvulsant lacosamide acts on Nav1.3, Nav1.7, and Nav1.8. The aim of this study was to evaluate the efficacy, safety, and tolerability of lacosamide as a potential treatment for pain in Nav1.7-related small fibre neuropathy. The Lacosamide-Efficacy-'N'-Safety in SFN (LENSS) was a randomized, placebo-controlled, double-blind, crossover-design study. Subjects were recruited in the Netherlands between November 2014 and July 2016. Patients with Nav1.7-related small fibre neuropathy were randomized to start with lacosamide followed by placebo or vice versa. In both 8-week treatment phases, patients received 200 mg two times a day (BID), preceded by a titration period, and ended by a tapering period. The primary outcome was efficacy, defined as the proportion of patients with 1-point average pain score reduction compared to baseline using the Pain Intensity Numerical Rating Scale. The trial is registered with ClinicalTrials.gov, number NCT01911975. Twenty-four subjects received lacosamide, and 23 received placebo. In 58.3% of patients receiving lacosamide, mean average pain decreased by at least 1 point, compared to 21.7% in the placebo group [sensitivity analyses, odds ratio 5.65 (95% confidence interval: 1.83-17.41); P = 0.0045]. In the lacosamide group, 33.3% reported that their general condition improved versus 4.3% in the placebo group (P-value = 0.0156). Additionally, a significant decrease in daily sleep interference, and in surface pain intensity was demonstrated. No significant changes in quality of life or autonomic symptoms were found. Lacosamide was well tolerated and safe in use. This study shows that lacosamide has a significant effect on pain, general wellbeing, and sleep quality. Lacosamide was well tolerated and safe, suggesting that it can be used for pain treatment in Nav1.7-related small fibre neuropathy.
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the novel activity of carbamazepine as an activation modulator extends from Nav1.7 mutations to the nav1 8 s242t mutant channel from a patient with painful diabetic neuropathy
Molecular Pharmacology, 2018Co-Authors: Chongyang Han, Stephen G Waxman, Mark Estacion, Andreas C Themistocleous, Fadia B Dibhajj, Iulia Blesneac, Lawrence J Macala, C Fratter, David L H Bennett, Sulayman D DibhajjAbstract:Neuropathic pain in patients carrying sodium channel gain-of-function mutations is generally refractory to pharmacotherapy. However, we have shown that pretreatment of cells with clinically achievable concentration of carbamazepine (CBZ; 30 μM) depolarizes the voltage dependence of activation in some Nav1.7 mutations such as S241T, a novel CBZ mode of action of this drug. CBZ reduces the excitability of dorsal root ganglion (DRG) neurons expressing Nav1.7-S241T mutant channels, and individuals carrying the S241T mutation respond to treatment with CBZ. Whether the novel activation-modulating activity of CBZ is specific to Nav1.7, and whether this pharmacogenomic approach can be extended to other sodium channel subtypes, are not known. We report here the novel NaV1.8-S242T mutation, which corresponds to the Nav1.7-S241T mutation, in a patient with neuropathic pain and diabetic peripheral neuropathy. Voltage-clamp recordings demonstrated hyperpolarized and accelerated activation of NaV1.8-S242T. Current-clamp recordings showed that NaV1.8-S242T channels render DRG neurons hyperexcitable. Structural modeling shows that despite a substantial difference in the primary amino acid sequence of Nav1.7 and NaV1.8, the S242 (NaV1.8) and S241 (Nav1.7) residues have similar position and orientation in the domain I S4-S5 linker of the channel. Pretreatment with a clinically achievable concentration of CBZ corrected the voltage dependence of activation of NaV1.8-S242T channels and reduced DRG neuron excitability as predicted from our pharmacogenomic model. These findings extend the novel activation modulation mode of action of CBZ to a second sodium channel subtype, NaV1.8.
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sodium channel nav1 9 mutations associated with insensitivity to pain dampen neuronal excitability
Journal of Clinical Investigation, 2017Co-Authors: Jianying Huang, Alison Cutts, Paul Y Goldberg, Charles Jay Cohen, Sulayman D Dibhajj, Carlos G. Vanoye, Stephen G Waxman, Alfred L GeorgeAbstract:: Voltage-gated sodium channel (NaV) mutations cause genetic pain disorders that range from severe paroxysmal pain to a congenital inability to sense pain. Previous studies on Nav1.7 and NaV1.8 established clear relationships between perturbations in channel function and divergent clinical phenotypes. By contrast, studies of NaV1.9 mutations have not revealed a clear relationship of channel dysfunction with the associated and contrasting clinical phenotypes. Here, we have elucidated the functional consequences of a NaV1.9 mutation (L1302F) that is associated with insensitivity to pain. We investigated the effects of L1302F and a previously reported mutation (L811P) on neuronal excitability. In transfected heterologous cells, the L1302F mutation caused a large hyperpolarizing shift in the voltage-dependence of activation, leading to substantially enhanced overlap between activation and steady-state inactivation relationships. In transfected small rat dorsal root ganglion neurons, expression of L1302F and L811P evoked large depolarizations of the resting membrane potential and impaired action potential generation. Therefore, our findings implicate a cellular loss of function as the basis for impaired pain sensation. We further demonstrated that a U-shaped relationship between the resting potential and the neuronal action potential threshold explains why NaV1.9 mutations that evoke small degrees of membrane depolarization cause hyperexcitability and familial episodic pain disorder or painful neuropathy, while mutations evoking larger membrane depolarizations cause hypoexcitability and insensitivity to pain.
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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.
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.
Joel A Black - One of the best experts on this subject based on the ideXlab platform.
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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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Nav1.7 accumulates and co-localizes with phosphorylated ERK1/2 within transected axons in early experimental neuromas
Experimental neurology, 2011Co-Authors: Anna-karin Persson, Andreas Gasser, Joel A Black, Stephen G WaxmanAbstract:Abstract Peripheral nerve injury can result in formation of a neuroma, which is often associated with heightened sensitivity to normally innocuous stimuli as well as spontaneous dysesthesia and pain. The onset and persistence of neuropathic pain have been linked to spontaneous ectopic electrogenesis in axons within neuromas, suggesting an involvement of voltage-gated sodium channels. Sodium channel isoforms NaV1.3, Nav1.7 and NaV1.8 have been shown to accumulate in chronic painful human neuromas, while, to date, only NaV1.3 has been reported to accumulate within experimental neuromas. Although recent evidence strongly support a major contribution for Nav1.7 in nociception, the expression of Nav1.7 in injured axons within acute neuromas has not been studied. The current study examined whether Nav1.7 accumulates in experimental rat neuromas. We further investigated whether activated (phosphorylated) mitogen-activated protein (MAP) kinase ERK1/2, which is known to modulate Nav1.7 properties, is co-localized with Nav1.7 within axons in neuromas. We demonstrate increased levels of Nav1.7 in experimental rat sciatic nerve neuromas, 2 weeks after nerve ligation and transaction. We further show elevated levels of phosphorylated ERK1/2 within individual neuroma axons that exhibit Nav1.7 accumulation. These results extend previous descriptions of sodium channel and MAP kinase accumulation within experimental and human neuromas, and suggest that targeted blockade of Nav1.7 or ERK1/2 may provide a strategy for amelioration of chronic pain that often follows nerve injury and formation of neuromas.
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Contactin Associates with Sodium Channel Nav1.3 in Native Tissues and Increases Channel Density at the Cell Surface
The Journal of Neuroscience, 2004Co-Authors: Bhaval S. Shah, Sulayman D Dib-hajj, Anthony M. Rush, Joel A Black, Lynda Tyrrell, Stephen G WaxmanAbstract:The upregulation of voltage-gated sodium channel Nav1.3 has been linked to hyperexcitability of axotomized dorsal root ganglion (DRG) neurons, which underlies neuropathic pain. However, factors that regulate delivery of Nav1.3 to the cell surface are not known. Contactin/F3, a cell adhesion molecule, has been shown to interact with and enhance surface expression of sodium channels Nav1.2 and Nav1.9. In this study we show that contactin coimmunoprecipitates with Nav1.3 from postnatal day 0 rat brain where this channel is abundant, and from human embryonic kidney (HEK) 293 cells stably transfected with Nav1.3 (HEK-Nav1.3). Purified GST fusion proteins of the N and C termini of Nav1.3 pull down contactin from lysates of transfected HEK 293 cells. Transfection of HEK-Nav1.3 cells with contactin increases the amplitude of the current threefold without changing the biophysical properties of the channel. Enzymatic removal of contactin from the cell surface of cotransfected cells does not reduce the elevated levels of the Nav1.3 current. Finally, we show that, similar to Nav1.3, contactin is upregulated in axotomized DRG neurons and accumulates within the neuroma of transected sciatic nerve. We propose that the upregulation of contactin and its colocalization with Nav1.3 in axotomized DRG neurons may contribute to the hyper-excitablity of the injured neurons.
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Co-localization of sodium channel Nav1.6 and the sodium-calcium exchanger at sites of axonal injury in the spinal cord in EAE.
Brain, 2004Co-Authors: Matthew J. Craner, Albert C. Lo, Bryan C. Hains, Joel A Black, Stephen G WaxmanAbstract:Axonal degeneration contributes to the development of non‐remitting neurological deficits and disability in multiple sclerosis, but the molecular mechanisms that underlie axonal loss in multiple sclerosis are not clearly understood. Studies of white matter axonal injury have demonstrated that voltage‐gated sodium channels can provide a route for sodium influx into axons that triggers reverse operation of the Na+/Ca2+ exchanger (NCX) and subsequent influx of damaging levels of intra‐axonal calcium. The molecular identities of the involved sodium channels have, however, not been determined. We have previously demonstrated extensive regions of diffuse expression of Nav1.6 and Nav1.2 sodium channels along demyelinated axons in experimental allergic encephalomyelitis (EAE). Based on the hypothesis that the co‐localization of Nav1.6 and NCX along extensive regions of demyelinated axons may predispose these axons to injury, we examined the expression of myelin basic protein, Nav1.2, Nav1.6, NCX and β‐amyloid precursor protein (β‐APP), a marker of axonal injury, in the spinal cord dorsal columns of mice with EAE. We demonstrate a significant increase in the number of demyelinated axons demonstrating diffuse Nav1.6 and Nav1.2 sodium channel immunoreactivity in EAE (92.2 ± 2.1% of β‐APP positive axons were Nav1.6‐positive). Only 38.0 ± 2.9% of β‐APP positive axons were Nav1.2 positive, and 95% of these co‐expressed Nav1.6 together with Nav1.2. Using triple‐labelled fluorescent immunohistochemistry, we demonstrate that 73.5 ± 4.3% of β‐APP positive axons co‐express Nav1.6 and NCX, compared with 4.4 ± 1.0% in β‐APP negative axons. Our results indicate that co‐expression of Nav1.6 and NCX is associated with axonal injury in the spinal cord in EAE.
Dan Okura - 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.
