Further analysis of the mechanisms of action of batrachotoxin on the membrane of myelinated nerve

Bi, Khodorov; Revenko, S. V.

doi:10.1016/0306-4522(79)90159-3

Cited by 122 publications

(95 citation statements)

References 38 publications

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“…The difference in ion-selectivity does not mean necessarily that different structures are involved. It is known that activation of voltage-dependent, tetrodotoxinsensitive Na+ channels by a variety of neurotoxins is accompanied by a loss in the ion-selectivity (Khodorov & Revenko, 1979;Frelin et al, 1981). Second, whereas epithelial-like Na+ channels were most easily recorded in the cell-attached configuration, suggesting that as yet unidentified intracellular factors are required for their activity (Van Renterghem & Lazdunski, 1991) …”

Section: Electrophysiological Recordings and Analysismentioning

confidence: 99%

3,4 Dichlorobenzamil‐sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes

Renterghem

Frelin

1993

British J Pharmacology

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1 Smooth muscle cells were dispersed from rat aorta and then cultured. The action of palytoxin on rat aortic myocytes was analysed by measurement of 22Na+ uptake and single channel recording techniques. 2 Palytoxin induced an increase in 22Na+ uptake, with a concentration of 50 nM producing halfmaximal activation. The action of palytoxin was inhibited by amiloride derivatives and by ouabain. The concentrations of inhibitor producing half-maximal inhibition were 10 JIM for 3,4 dichlorobenzamil, 30 JAM for benzamil, 100 JAM for phenamil and 1 mm for ouabain. 3 In outside-out patches, palytoxin induced single channel currents that reversed near 0 mV with NaCl or KCI in the extracellular solution, but were outward with N-methyl-D-glucamine chloride or CaCl2 ( 10 mM), indicating that palytoxin induced a cation channel permeable to Na+ and K+ (PK/PNa = 1.2) but not to Ca2+ (PK/PCa > 30) or to N-methyl-D-glucamine (NMDG) (PK/PNMDG> 11). The unit channel conductance was 11 -14 pS. 4 A high (>0.1 mM) extracellular concentration of Ca2+ was necessary to observe channel activation by palytoxin. A high (150 mM) extracellular concentration of K+ partially prevented and reversed channel activation by palytoxin. 5 The channel activity was fully blocked by 3,4 dichlorobenzamil (20 JAM) and partially blocked by phenamil (50 JM). It was not reduced by ouabain (200 JAM).

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Section: Electrophysiological Recordings and Analysismentioning

confidence: 99%

3,4 Dichlorobenzamil‐sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes

Renterghem

Frelin

1993

British J Pharmacology

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“…Batrachotoxin (BTX) 4 is a steroidal sodium-channel agonist, which was first isolated from the skin of the Colombian frog Phyllobates bicolor (14). BTX binds preferentially to the open Na V channels (15)(16)(17) and alters several channel properties. First, it shifts the voltage dependence of activation in the hyperpolarizing direction, thus causing the channel to open at more negative membrane potentials.…”

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confidence: 99%

“…Architecture of voltage-gated potassium channels is inconsistent with a scenario that a lipid-exposed ligand simultaneously binds to more than two inner helices. A unitary Hill coefficient of BTX action (17) and largely different amino acid sequences of the four repeats rule out a possibility that the channel contains more than one BTX receptor (17, 26 -28). Although allosteric effects could explain the modifications of channel conductance, ion selectivity, and gating by BTX (29), another possibility could be that BTX is directly exposed to the permeation pathway (5,30).…”

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confidence: 99%

Identification of New Batrachotoxin-sensing Residues in Segment IIIS6 of the Sodium Channel

Garden

Wang

et al. 2011

Journal of Biological Chemistry

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Ion permeation through voltage-gated sodium channels is modulated by various drugs and toxins. The atomistic mechanisms of action of many toxins are poorly understood. A steroidal alkaloid batrachotoxin (BTX) causes persistent channel activation by inhibiting inactivation and shifting the voltage dependence of activation to more negative potentials. Traditionally, BTX is considered to bind at the channel-lipid interface and allosterically modulate the ion permeation. However, amino acid residues critical for BTX action are found in the inner helices of all four repeats, suggesting that BTX binds in the pore. In the octapeptide segment IFGSFFTL in IIIS6 of a cockroach sodium channel BgNa V , besides Ser_3i15 and Leu_3i19, which correspond to known BTX-sensing residues of mammalian sodium channels, we found that Gly_3i14 and Phe_3i16 are critical for BTX action. Using these data along with published data as distance constraints, we docked BTX in the Kv1.2-based homology model of the open BgNa V channel. We arrived at a model in which BTX adopts a horseshoe conformation with the horseshoe plane normal to the pore axis. The BTX ammonium group is engaged in cation-interactions with Phe_3i16 and BTX moieties interact with known BTX-sensing residues in all four repeats. Oxygen atoms at the horseshoe inner surface constitute a transient binding site for permeating cations, whereas the bulky BTX molecule would resist the pore closure, thus causing persistent channel activation. Our study reinforces the concept that steroidal sodium channel agonists bind in the inner pore of sodium channels and elaborates the atomistic mechanism of BTX action.Voltage-gated sodium channels (Na V ) are responsible for the rapid rising phase of the action potential in nerve and muscle cells. The pore-forming ␣-subunit of Na V channels contains four repeats, and each repeat has six transmembrane helices (S1-S6). The S1-S4 helices form the voltage sensor domain.Positively charged S4 helices move outward in response to membrane depolarization. The S5 and S6 helices contribute to the pore-forming domain. The extracellular linkers connecting S5 and S6 helices form the four re-entrant P-loops, which contain the selectivity filter residues. In the absence of x-ray structures of Na V channels, their homology models, which are based on x-ray structures of potassium channels, are used to explain structure-activity relationships of various sodium channel ligands, including local anesthetics (1-4), steroidal activators (5-8), and pyrethroid insecticides (9, 10). Recent reinterpretation of data on substituted cysteine accessibility of the Ca V 2.1 channel (11) in view of a the channel homology model, which is based on the x-ray structure of the open voltage-gated potassium channel Kv1.2 (12), further supports a general similarity of the inner pore architecture in different voltage-gated cationic channels (13).Sodium channels are targets for numerous drugs and naturally occurring toxins. Batrachotoxin (BTX) 4 is a steroidal sodium-channel agonist, which...

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“…BTX profoundly alters various aspects of sodium channel behavior. Voltage-dependent activation is shifted to more negative potentials, inactivation is disabled, and pore conductance and selectivity are altered (Khodorov and Revenko, 1979;Khodorov et al, 1981;Quandt and Narahashi, 1982;Tanguy and Yeh, 1991;Wang and Wang, 1994). Modification of sodium channels by BTX requires channel activation.…”

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confidence: 99%

The Batrachotoxin Receptor on the Voltage-Gated Sodium Channel is Guarded by the Channel Activation Gate

Hadid

Ragsdale

2002

Mol Pharmacol

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Batrachotoxin (BTX), from South American frogs of the genusPhyllobates, irreversibly activates voltage-gated sodium channels. Previous work demonstrated that a phenylalanine residue approximately halfway through pore-lining transmembrane segment IVS6 is a critical determinant of channel sensitivity to BTX. In this study, we introduced a series of mutations at this site in the Na v 1.3 sodium channel, expressed wild-type and mutant channels in Xenopus laevis oocytes, and examined their sensitivity to BTX using voltage clamp recording. We found that substitution of either alanine or isoleucine strongly reduced channel sensitivity to toxin, whereas cysteine, tyrosine, or tryptophan decreased toxin action only modestly. These data suggest an electrostatic ligand-receptor interaction at this site, possibly involving a charged tertiary amine on BTX. We then used a mutant channel (mutant F1710C) with intermediate toxin sensitivity to examine the properties of the toxin-receptor reaction in more detail. In contrast to wild-type channels, which bind BTX almost irreversibly, toxin dissociation from mutant channels was rapid, but only when the channels were open, not when they were closed. These data suggest the closed activation gate trapped bound toxin. Although BTX dissociation required channel activation, it was, paradoxically, slowed by strong membrane depolarization, suggesting additional statedependent and/or electrostatic influences on the toxin binding reaction. We propose that BTX moves to and from its receptor through the cytoplasmic end of the open ion-conducting pore, in a manner similar to that of quaternary local anesthetics like QX314.

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Further analysis of the mechanisms of action of batrachotoxin on the membrane of myelinated nerve

Cited by 122 publications

References 38 publications

3,4 Dichlorobenzamil‐sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes

3,4 Dichlorobenzamil‐sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes

Identification of New Batrachotoxin-sensing Residues in Segment IIIS6 of the Sodium Channel

The Batrachotoxin Receptor on the Voltage-Gated Sodium Channel is Guarded by the Channel Activation Gate

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