Effect of batrachotoxin on the electroplax of electric eel: evidence for voltage-dependent interaction with sodium channels.
Batrachotoxin under certain conditions has a strong depolarizing effect on the innervated membrane of the monocellular electroplax preparation from the electric eel, El-ectrophorus electricus. No effect is observed when the toxin (50-200 nM) is applied to the resting membrane for periods up to 1 hr. However, if the membrane is exposed to batrachotoxin  and the cell is subjected to stimulation at a stimulus voltage slightly above the threshold for action potential firing, a progressive prolongation of the action potential and concomitant progressive depolarization of the innervated membrane is observed. When the membrane is depolarized by 15-20 mV, a further abrupt all-or-none depolarization occurs, and the potential attains a steady-state value between 0 and -10 mV. Brief stimulation of a cell in the presence of batrachotoxin is sufficient to define a batrachotoxin-treated cell, even though negligible depolarization occurs. If depolarizing agents such as carbamoylcholine or potassium chloride are introduced to such a cell in concentrations that normally produce a 20-30 mV depolarization, the abrupt all-or-none depolarization immediately occurs. All-or-none depolarizations arising from either electrical stimulation or depolarizing agents are unaffected by d-tubocurarine but are completely reversed by tetrodotoxin. Batrachotoxin thus appears to activate only the action potential sodium channels. In the batrachotoxin-treated membrane, these channels can attain stable steady states in either a closed configuration at the normal resting potential or in an open configuration after complete depolarization. A striking hysteresis cycle thus can be generated, which is strongly indicative of a voltage-dependent interaction of the toxin with the action potential sodium channels.
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D001496:Batrachotoxins / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology; D004347:Drug Interactions; D004557:Electric Organ / Q000187:drug effects* / Q000378:metabolism; D004593:Electrophorus; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013570:Synaptic Membranes / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
D001496:Batrachotoxins; D013779:Tetrodotoxin; D002217:Carbachol; D012964:Sodium; D011188:Potassium