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B. W. Urban - One of the best experts on this subject based on the ideXlab platform.
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Steady-State Gating of Batrachotoxin-modified Sodium Channels Variability and Electrolyte-dependent Modulation
2013Co-Authors: L. D. Chabala, B. W. Urban, L. B. Wexss, W. N. Green, S. AndersenAbstract:A B S T RA CT The steady-state gating of individual Batrachotoxin-modified sodium channels in neutral phospholipid bilayers exhibits spontaneous, reversible changes in channel activation, such that the midpoint potential (V~) for the gating curves may change, by 30 mV or more, with or without a change in the apparent gating valence (za). Consequently, estimates for V a and, in particular, z a from ensembleaveraged gating curves differ from the average values for V, and z ~ from singlechannel gating curves. In addition to these spontaneous variations, the average Va shifts systematically as a function of [NaCI] (being- 109,-88, and-75 mV at 0.1, 0.5, and 1.0 M NaCI), with no systematic variation in the average z a ( ~ 3.7). The [NaC1]-dependent shifts in V ~ were interpreted in terms of screening of fixed charges near the channels ' gating machinery. Estimates for the extracellular and intracellular apparent charge densities ( ~ =-0.7 and cr ~ =-0.08 e/nm ~) were obtained from experiments in symmetrical and asymmetrical NaCI solutions using the Gouy-Chapman theory. In 0.1 M NaCI the extracellular and intracellular surface potentials are estimated to be-94 and-17 mV, respectively. The intrinsi
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Pharmacological modification of sodium channels from the human heart atrium in planar lipid bilayers: electrophysiological characterization of responses to Batrachotoxin and pentobarbital.
European journal of anaesthesiology, 2003Co-Authors: H. C. Wartenberg, J. P. Wartenberg, B. W. UrbanAbstract:Summary Background and objective: To investigate the effects of barbiturates on Batrachotoxin-modified sodium channels from different regions of the human heart. Single sodium channels from human atria were studied and compared with existing data from the human ventricle and from the central nervous system. Methods: Sodium channels from preparations of human atrial muscle were incorporated into planar lipid bilayers in the presence of Batrachotoxin, a sodium channel activator. The steady-state behaviour of single sodium channels was recorded in symmetrical 500 mmol NaCl before and after the addition of pentobarbital 0.34 ‐1.34 mmol. Results: The Batrachotoxin-treated human atrial sodium channel had an average single-channel conductance of 23.8 6 1.6 pS in symmetrical 500 mmol NaCl and a channel fractional open time of 0.83 6 0.06. The activation mid-point potential was 298.0 6 2.3 mV. Extracellular tetrodotoxin (a specific sodium channel blocking agent) blocked these channels with a k 1/2 5 0.53 µ mol at 0 mV. Pentobarbital reduced the time average conductance of single atrial sodium channels in a concentration-dependent manner (ID 50 5 0.71 mmol). In the same way, the steady-state activation was shifted to more hyperpolarized potentials ( 210.6 mV at 0.67 mmol pentobarbital). Conclusions: The properties of Batrachotoxin-modified sodium channels from human atrial tissue did not differ greatly from those described for ventricular sodium channels in the literature. Our data yielded no explanation for the observed functional diversity. However, cardiac sodium channels differ from those found in the central nervous system.
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the voltage dependent action of pentobarbital on Batrachotoxin modified human brain sodium channels
Biochimica et Biophysica Acta, 1994Co-Authors: Benno Rehberg, Daniel S Duch, B. W. UrbanAbstract:The voltage-dependent action of the intravenous anesthetic pentobarbital on human brain sodium channels activated by Batrachotoxin was examined using planar lipid bilayer methods. Fractional open time-data were fitted by Boltzmann functions to yield simple parameters characterizing the voltage-dependence of the fractional open time. Pentobarbital caused a dose-dependent reduction of the maximum fractional open time of the sodium channel and a shift of the potential of half-maximal open time towards hyperpolarized potentials, whereas the slope parameter of the Boltzmann-fits was unaffected. A statistically significant increase of the variability of these parameters was found only in the case of the maximum fractional open time, indicating a random fluctuation of pentobarbital-induced suppression of the sodium channels over time. The voltage-dependent action of pentobarbital probably results from either a pentobarbital-modification of channel activation gating and/or a modification of the pentobarbital action by the gating process itself.
Ging Kuo Wang - One of the best experts on this subject based on the ideXlab platform.
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Binding of Benzocaine in Batrachotoxin-modified Na + Channels State-dependent Interactions
2013Co-Authors: Ging Kuo Wang, Shoya WangAbstract:a modulated receptor hypothesis (MRH) to explain the action of benzocaine in voltage-gated Na ÷ channels. Using the MRH as a framework, we examined benzocaine binding in Batrachotoxin (BTX)-modified Na + channels under voltageclamp conditions using either step or ramp command signals. We found that benzocaine binding is strongly voltage dependent. At-70 mV, the concentration of benzocaine that inhibits 50 % of BTX-modified Na ÷ currents in GHa cells (ICs0) is 0.2 raM, whereas at +50 mV, the IC~0 is 1.3 raM. Dose-response curves indicate that only one molecule of benzocaine is required to bind with one BTX-modified Na + channel at-70 mV, whereas approximately two molecules are needed at +50 inV. Upon treatment with the inactivation modifier chloramine-T, the binding affinity of benzocaine is reduced significantly at-70 mV, probably as a result of the removal of the inactivated state of BTX-modified Na + channels. The same treatment, however, enhances the binding affinity of cocaine near this voltage. External Na + ions appear to have little effect on benzocaine binding, although they do affect cocaine binding. We conclude that two mechanisms underlie the action of local anesthetics in BTX-modified Na + channels. Unlike open-channel blockers such as cocaine and bupivacaine, neutral benzocaine binds preferentially with BTX-modifled Na ÷ channels in a closed state. Furthermore, benzocaine can be modified chemically so that it behaves like an open-channel blocker. This compound also elicits a use-dependent block in unmodified Na + channels after repetitive depolarizations, whereas benzocaine does not. The implications of these findings for the MRH theory will be discussed
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Cocaine-induced Closures of Single Batrachotoxin-activated Na + Channels in
2013Co-Authors: Planar Lipid Bilayers, Ging Kuo WangAbstract:ABSTRACT Batrachotoxin (BTX)-activated Na + channels from rabbit skeletal muscle were incorporated into planar lipid bilayers. These channels appear to open most of the time at voltages>- 60 mV. Local anesthetics, including QX-314, bupivacalne, and cocaine when applied internally, induce different durations of channel closures and can be characterized as "fast " (mean closed duration < 10 ms at +50 mV), "intermediate " (~80 ms), and "slow " (~400 ms) blockers, respectively. The action of these local anesthetics on the Na + channel is voltage dependent; larger depolarizations give rise to stronger binding interactions. Both the dose-response curve and the kinetics of the cocaine-induced closures indicate that there is a single class of cocaine-binding site. QX-314, though a quaternary-amine local anesthetic, apparently competes with the same binding site. External cocaine or bupivacaine application is almost as effective as internal application, whereas external QX-314 is ineffective. Interestingly, external Na + ions reduce the cocaine binding affinity drastically, whereas internal Na + ions have little effect. Both the cocaine association and dissociation rate constants are altered when external Na + ion concentrations are raised. We conclude that (a) one cocaine molecule closes one BTX-activated Na + channel in an all-or-none manner, (b) the binding affinity of cocaine is voltage sensitive, (c) this cocaine binding site can be reached by a hydrophilic pathway through internal surface and by a hydrophobic pathway through bilayer membrane, and (d) that this binding site interacts indirectly with the Na + ions. A direct interaction between the receptor and Na + ions seems minimal
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Quaternary Ammonium Compounds as Structural Probes of Single Batrachotoxin-activated Na + Channels
2013Co-Authors: Ging Kuo Wang, Rachelle Simon, Shoya WangAbstract:ABSTRACT Quaternary ammonium (QA) blockers are well-known structural probes for studying the permeation pathway of voltage-gated K + channels. In this study we have examined the effects of a series of n-alkyl-trimethylammonium compounds (Cn-QA) on Batrachotoxin (BTX)-activated Na + channels from skeletal muscle incorporated into planar lipid bilayers. We found that these amphipathic QA compounds (C,-QA where n = 10-18) block single Na ÷ channels preferentially from the internal side with equilibrium dissociation constants (KD) in the submicromolar to micromolar range. External application of amphipathic QA compounds is far less effective, by a factor of> 200. The block can be described by a QA molecule binding to a single site in the Na ÷ channel permeation pathway. QA binding affinity is dependent on transmembrane voltage with an effective valence (B) of ~ 0.5. QA dwell times (given as mean closed times, ~c) increase as a function of n-alkyl chain length, ranging from ~ 13 ms for C~0-QA to 500 ms for Cts-QA at +50 inV. The results imply that there is a large hydrophobic region within the Na ÷ channel pore which accepts up to 18 methylene groups of the C.-QA cation. This hydrophobic domain may be of clinical significance since it also interacts with local anesthetics such as cocaine and mepivacaine. Finally, like BTX-activated Na ÷ channels in bilayers, unmodified Na ÷ channels in GH 3 cells are also susceptible to QA block. Amphipathic QA cations elicit both tonic and use-dependent inhibitions of normal Na + currents in a manner similar to that of local anesthetic cocaine. We conclude that amphipathic QA compounds are valuable structural probes to study the permeation pathway of both normal and BTX-activated Na ÷ channels
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voltage gated sodium channels as primary targets of diverse lipid soluble neurotoxins
Cellular Signalling, 2003Co-Authors: Shoya Wang, Ging Kuo WangAbstract:Abstract Voltage-gated Na+ channels are heteromeric membrane glycoproteins responsible for the generation of action potentials. A number of diverse lipid-soluble neurotoxins, such as Batrachotoxin, veratridine, aconitine, grayanotoxins, pyrethroid insecticides, brevetoxins and ciguatoxin, target voltage-gated Na+ channels for their primary actions. These toxins promote Na+ channel opening, induce depolarization of the resting membrane potential, and thus drastically affect the excitability of nerve, muscle and cardiac tissues. Poisoning by these lipid-soluble neurotoxins causes hyperexcitability of excitable tissues, followed by convulsions, paralysis and death in animals. How these lipid-soluble neurotoxins alter Na+ channel gating mechanistically remains unknown. Recent mapping of receptor sites within the Na+ channel protein for these neurotoxins using site-directed mutagenesis has provided important clues on this subject. Paradoxically, the receptor site for Batrachotoxin and veratridine on the voltage-gated Na+ channel α-subunit appears to be adjacent to or overlap with that for therapeutic drugs such as local anaesthetics (LAs), antidepressants and anticonvulsants. This article reviews the physiological actions of lipid-soluble neurotoxins on voltage-gated Na+ channels, their receptor sites on the S6 segments of the Na+ channel α-subunit and a possible linkage between their receptors and the gating function of Na+ channels.
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modification of wild type and Batrachotoxin resistant muscle µ1 na channels by veratridine
Pflügers Archiv: European Journal of Physiology, 2000Co-Authors: Ging Kuo Wang, C Quan, Margaret Seaver, Shoya WangAbstract:Biochemical evidence indicates that veratridine (VTD) and Batrachotoxin (BTX) share a common binding site in Na+ channels. Under whole-cell voltage-clamp conditions, we examined this single receptor hypothesis by studying the VTD phenotype in BTX-resistant muscle Na+ channels, µ1-I433K, N434K, L437K, F1579K, and N1584K. Derived from point mutations at segments D1–S6 and D4–S6, these mutant Na+ channels are resistant to 5 µM BTX when expressed in human embryonic kidney cells. In contrast to the wild-type phenotype, VTD at 200 µM elicits little or no maintained current during a test pulse at +50 mV, and little or no "tail" current after the test pulse in all BTX-resistant mutant channels. Paradoxically, VTD retains its ability to inhibit the peak Na+ current in BTX-resistant mutant Na+ channels. To explain these mutant phenotypes, we propose a two-step binding reaction scheme. An initial VTD-binding interaction with the Na+ channel results in the inhibition of peak current amplitude, and a second binding reaction results in the trapping of VTD within the D1–S6 and D4–S6 domain interface. The failure of BTX-resistant mutant Na+ channels to trap VTD suggests that segments of D1–S6 and D4–S6 form a common receptor for VTD and BTX.
Masayuki Inoue - One of the best experts on this subject based on the ideXlab platform.
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synthesis of the tetracyclic structure of Batrachotoxin enabled by bridgehead radical coupling and pd ni promoted ullmann reaction
Organic Letters, 2018Co-Authors: Komei Sakata, Daisuke Urabe, Yinghua Wang, Masayuki InoueAbstract:The steroidal ABCD-ring system of the potent neurotoxin Batrachotoxin was efficiently assembled in a convergent fashion. Bridgehead radical coupling between the simple AB-ring and D-ring fragments (3 and 4) formed the sterically congested linkage at the C9-oxygen-attached tetrasubstituted carbon. The C-ring was then cyclized by the Pd/Ni-promoted Ullmann reaction of the vinyl triflate and vinyl bromide of 19, giving rise to tetracyclic structure 1.
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Synthesis of the Tetracyclic Structure of Batrachotoxin Enabled by Bridgehead Radical Coupling and Pd/Ni-Promoted Ullmann Reaction
2017Co-Authors: Komei Sakata, Daisuke Urabe, Yinghua Wang, Masayuki InoueAbstract:The steroidal ABCD-ring system of the potent neurotoxin Batrachotoxin was efficiently assembled in a convergent fashion. Bridgehead radical coupling between the simple AB-ring and D-ring fragments (3 and 4) formed the sterically congested linkage at the C9-oxygen-attached tetrasubstituted carbon. The C-ring was then cyclized by the Pd/Ni-promoted Ullmann reaction of the vinyl triflate and vinyl bromide of 19, giving rise to tetracyclic structure 1
John W Daly - One of the best experts on this subject based on the ideXlab platform.
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Alkaloids from amphibian skin: a tabulation of over eight-hundred compounds.
Journal of natural products, 2005Co-Authors: John W Daly, Thomas F SpandeAbstract:A diverse array of biologically active, lipid-soluble alkaloids have been discovered in amphibian skin. Such alkaloids include the following: the steroidal samandarines from salamanders, the Batrachotoxins, histrionicotoxins, gephyrotoxins, and epibatidine from neotropical poison frogs (Dendrobatidae), the pumiliotoxins, allopumiliotoxins, homopumiliotoxins, and decahydroquinolines from certain genera of anurans from four families (Dendrobatidae, Mantellidae, Bufonidae, and Myobatrachidae), a variety of izidines (pyrrolizidines, indolizidines, quinolizidines, lehmizidines), pyrrolidines, piperidines, various tricyclics (related in structures to the coccinellines), and spiropyrrolizidines from the first three of these four families, the pseudophrynamines from one genus of Australian frogs, and a variety of unclassified alkaloids as yet of undetermined structure. With the exception of the samandarines and the pseudophrynamines, all alkaloids appear to be derived from dietary sources. Although only a few of...
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melyrid beetles choresine a putative source for the Batrachotoxin alkaloids found in poison dart frogs and toxic passerine birds
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: John P Dumbacher, Avit Wako, Scott R Derrickson, Allan Samuelson, John W DalyAbstract:Batrachotoxins are neurotoxic steroidal alkaloids first isolated from a Colombian poison-dart frog and later found in certain passerine birds of New Guinea. Neither vertebrate group is thought to produce the toxins de novo, but instead they likely sequester them from dietary sources. Here we describe the presence of high levels of Batrachotoxins in a little-studied group of beetles, genus Choresine (family Melyridae). These small beetles and their high toxin concentrations suggest that they might provide a toxin source for the New Guinea birds. Stomach content analyses of Pitohui birds revealed Choresine beetles in the diet, as well as numerous other small beetles and arthropods. The family Melyridae is cosmopolitan, and relatives in Colombian rain forests of South America could be the source of the Batrachotoxins found in the highly toxic Phyllobates frogs of that region.
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alkaloids from frog skin the discovery of epibatidine and the potential for developing novel non opioid analgesics
Natural Product Reports, 2000Co-Authors: John W Daly, Martin H Garraffo, Michael W Decker, James P Sullivan, Michael WilliamsAbstract:Research on the nature, structure and biological activity of the toxins present in the skin of poison-dart frogs of South America began in the Laboratory of Chemistry at the National Institutes of Health in the mid-1960s. The presence of toxins in the skin of such frogs had been discovered long ago by Indians of Western Colombia, who to this day use skin secretions from three Colombian species of dendrobatid frogs (genus Phyllobates) to poison the grooved tips of blow darts used in hunting small game and birds. Initial field work on a poison-dart frog of the Rio San Juan drainage, and preparation of extracts was first conducted by F. Marki in 1962 and then by Daly in 1964 and 1966. The toxic principles were isolated and proved on structural analysis to be steroidal alkaloids, which were named Batrachotoxins.1 These were then shown to be specific and potent activators of sodium channels.2 Both the natural alkaloids and a radioactive analog have proven to be invaluable research tools for the study of sodium channels and their interaction with local anesthetics, anticonvulsants, antiarrythmics and other drugs.3 The structure of Batrachotoxin and other alkaloids, subsequently isolated from frog skin, are shown in Fig. 1. These initial studies on the Batrachotoxin alkaloids from the poison-dart frogs of Western Colombia might never have been extended to some sixty species of poison-frogs of the neotropical family Dendrobatidae, had not Charles W. Myers, a herpetologist working on the reptiles and amphibians of Panama, contacted Daly and proposed a collaboration on the toxicity of an extremely variable dendrobatid frog (genus Dendrobates) of the Bocas Archipelago of Panama. The initial hypothesis, namely that the more brightly colored populations would contain higher levels of toxic alkaloids, proved incorrect. However, the analyses revealed not the steroidal Batrachotoxins, but instead a variety of simpler bicyclic alkaloids, including the relatively toxic pumiliotoxins and relatively nontoxic decahydroquinolines.4 The pumiliotoxins and related alkaloids later were shown to be potent myotonic/cardiotonic agents5 with modulatory effects on sodium channels.6 The initial field work by Myers and Daly led to a thirty year friendship and collaboration with the aim of analyzing the distribution, nature, structure and biological activity of alkaloids in frog skin. A major field trip by Myers and Daly in the early 1970s led to the isolation and structural determination of relatively nontoxic bicyclic histrionicotoxins,7 later established as highaffinity noncompetitive blockers of nicotinic acetylcholine receptor-channels (nAChRs).3 Over the next three decades more than 500 alkaloids of at least two dozen structural classes were discovered, most of which have, as yet, not been found elsewhere in nature.8,9 This is remarkable, since the dendrobatid frogs apparently do not synthesize any of their skin alkaloids, but instead sequester them unchanged into skin glands from dietary sources10 to be used as secreted chemical deterrents to predators. The search over the past five years for the dietary sources of the Batrachotoxins, pumiliotoxins and histrionicotoxins has been frustrating, but some six classes of relatively simple decahydroquinolines, piperidines, pyrrolidines and “izidines” of dendrobatid frog skin have been found in ants, while certain of the tricyclic and spiropyrrolizidine alkaloids occur in beetles and millipedes, respectively.10,11 Fig. 1 Structures of epibatidine and other alkaloids discovered in skin extracts from poison frogs (family Dendrobatidae). Batrachotoxin from Colombian Phyllobates aurotaenia,1 pumiliotoxin B from Panamanian Dendrobates pumilio,4 histrionicotoxin from Colombian Dendrobates histrionicus,7 and epibatidine and alkaloids 251D, 251H and 341A from Ecuadorian Epipedobates tricolor.12–14,16 EMINENT SCIENTIST REVIEW
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HomoBatrachotoxin in the genus Pitohui: chemical defense in birds?
Science (New York N.Y.), 1992Co-Authors: John P Dumbacher, Bruce M. Beehler, John W DalyAbstract:Three passerine species in the genus Pitohui, endemic to the New Guinea subregion, contain the steroidal alkaloid homoBatrachotoxin, apparently as a chemical defense. Toxin concentrations varied among species but were always highest in the skin and feathers. HomoBatrachotoxin is a member of a class of compounds collectively called Batrachotoxins that were previously considered to be restricted to neotropical poison-dart frogs of the genus Phyllobates. The occurrence of homoBatrachotoxin in pitohuis suggests that birds and frogs independently evolved this class of alkaloids.
Shoya Wang - One of the best experts on this subject based on the ideXlab platform.
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Binding of Benzocaine in Batrachotoxin-modified Na + Channels State-dependent Interactions
2013Co-Authors: Ging Kuo Wang, Shoya WangAbstract:a modulated receptor hypothesis (MRH) to explain the action of benzocaine in voltage-gated Na ÷ channels. Using the MRH as a framework, we examined benzocaine binding in Batrachotoxin (BTX)-modified Na + channels under voltageclamp conditions using either step or ramp command signals. We found that benzocaine binding is strongly voltage dependent. At-70 mV, the concentration of benzocaine that inhibits 50 % of BTX-modified Na ÷ currents in GHa cells (ICs0) is 0.2 raM, whereas at +50 mV, the IC~0 is 1.3 raM. Dose-response curves indicate that only one molecule of benzocaine is required to bind with one BTX-modified Na + channel at-70 mV, whereas approximately two molecules are needed at +50 inV. Upon treatment with the inactivation modifier chloramine-T, the binding affinity of benzocaine is reduced significantly at-70 mV, probably as a result of the removal of the inactivated state of BTX-modified Na + channels. The same treatment, however, enhances the binding affinity of cocaine near this voltage. External Na + ions appear to have little effect on benzocaine binding, although they do affect cocaine binding. We conclude that two mechanisms underlie the action of local anesthetics in BTX-modified Na + channels. Unlike open-channel blockers such as cocaine and bupivacaine, neutral benzocaine binds preferentially with BTX-modifled Na ÷ channels in a closed state. Furthermore, benzocaine can be modified chemically so that it behaves like an open-channel blocker. This compound also elicits a use-dependent block in unmodified Na + channels after repetitive depolarizations, whereas benzocaine does not. The implications of these findings for the MRH theory will be discussed
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Quaternary Ammonium Compounds as Structural Probes of Single Batrachotoxin-activated Na + Channels
2013Co-Authors: Ging Kuo Wang, Rachelle Simon, Shoya WangAbstract:ABSTRACT Quaternary ammonium (QA) blockers are well-known structural probes for studying the permeation pathway of voltage-gated K + channels. In this study we have examined the effects of a series of n-alkyl-trimethylammonium compounds (Cn-QA) on Batrachotoxin (BTX)-activated Na + channels from skeletal muscle incorporated into planar lipid bilayers. We found that these amphipathic QA compounds (C,-QA where n = 10-18) block single Na ÷ channels preferentially from the internal side with equilibrium dissociation constants (KD) in the submicromolar to micromolar range. External application of amphipathic QA compounds is far less effective, by a factor of> 200. The block can be described by a QA molecule binding to a single site in the Na ÷ channel permeation pathway. QA binding affinity is dependent on transmembrane voltage with an effective valence (B) of ~ 0.5. QA dwell times (given as mean closed times, ~c) increase as a function of n-alkyl chain length, ranging from ~ 13 ms for C~0-QA to 500 ms for Cts-QA at +50 inV. The results imply that there is a large hydrophobic region within the Na ÷ channel pore which accepts up to 18 methylene groups of the C.-QA cation. This hydrophobic domain may be of clinical significance since it also interacts with local anesthetics such as cocaine and mepivacaine. Finally, like BTX-activated Na ÷ channels in bilayers, unmodified Na ÷ channels in GH 3 cells are also susceptible to QA block. Amphipathic QA cations elicit both tonic and use-dependent inhibitions of normal Na + currents in a manner similar to that of local anesthetic cocaine. We conclude that amphipathic QA compounds are valuable structural probes to study the permeation pathway of both normal and BTX-activated Na ÷ channels
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voltage gated sodium channels as primary targets of diverse lipid soluble neurotoxins
Cellular Signalling, 2003Co-Authors: Shoya Wang, Ging Kuo WangAbstract:Abstract Voltage-gated Na+ channels are heteromeric membrane glycoproteins responsible for the generation of action potentials. A number of diverse lipid-soluble neurotoxins, such as Batrachotoxin, veratridine, aconitine, grayanotoxins, pyrethroid insecticides, brevetoxins and ciguatoxin, target voltage-gated Na+ channels for their primary actions. These toxins promote Na+ channel opening, induce depolarization of the resting membrane potential, and thus drastically affect the excitability of nerve, muscle and cardiac tissues. Poisoning by these lipid-soluble neurotoxins causes hyperexcitability of excitable tissues, followed by convulsions, paralysis and death in animals. How these lipid-soluble neurotoxins alter Na+ channel gating mechanistically remains unknown. Recent mapping of receptor sites within the Na+ channel protein for these neurotoxins using site-directed mutagenesis has provided important clues on this subject. Paradoxically, the receptor site for Batrachotoxin and veratridine on the voltage-gated Na+ channel α-subunit appears to be adjacent to or overlap with that for therapeutic drugs such as local anaesthetics (LAs), antidepressants and anticonvulsants. This article reviews the physiological actions of lipid-soluble neurotoxins on voltage-gated Na+ channels, their receptor sites on the S6 segments of the Na+ channel α-subunit and a possible linkage between their receptors and the gating function of Na+ channels.
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modification of wild type and Batrachotoxin resistant muscle µ1 na channels by veratridine
Pflügers Archiv: European Journal of Physiology, 2000Co-Authors: Ging Kuo Wang, C Quan, Margaret Seaver, Shoya WangAbstract:Biochemical evidence indicates that veratridine (VTD) and Batrachotoxin (BTX) share a common binding site in Na+ channels. Under whole-cell voltage-clamp conditions, we examined this single receptor hypothesis by studying the VTD phenotype in BTX-resistant muscle Na+ channels, µ1-I433K, N434K, L437K, F1579K, and N1584K. Derived from point mutations at segments D1–S6 and D4–S6, these mutant Na+ channels are resistant to 5 µM BTX when expressed in human embryonic kidney cells. In contrast to the wild-type phenotype, VTD at 200 µM elicits little or no maintained current during a test pulse at +50 mV, and little or no "tail" current after the test pulse in all BTX-resistant mutant channels. Paradoxically, VTD retains its ability to inhibit the peak Na+ current in BTX-resistant mutant Na+ channels. To explain these mutant phenotypes, we propose a two-step binding reaction scheme. An initial VTD-binding interaction with the Na+ channel results in the inhibition of peak current amplitude, and a second binding reaction results in the trapping of VTD within the D1–S6 and D4–S6 domain interface. The failure of BTX-resistant mutant Na+ channels to trap VTD suggests that segments of D1–S6 and D4–S6 form a common receptor for VTD and BTX.
