Batrachotoxin protects sodium channels from the blocking action of oenanthotoxin
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The blocking action of oenanthotoxin (OETX) and butanol on Na+ channels was studied in voltage clamp experiments on single myelinated nerve fibres treated by batrachotoxin (BTX).
OETX (40 μM) blocked Na+ currents through normal channels but did not affect significantly the BTX modified Na+ current.
BTX removed the depolarization-induced charge immobilization and slowed down significantly the OFF charge movement. However, the maximum charge displaced, as well as the kinetics of the ON charge movement during a strong membrane depolarization, remained unchanged.
OETX blocked the charge movement in normal Na+ channels but did not affect noticeably the charge movement modified by BTX.
BTX did not modify the K+ currents and did not protect them from the blocking action of OETX.
Butanol (0.01–0.1 M) decreased almost identically and reversibly both normal and BTX-modified Na+ currents.
It is concluded that binding of BTX to its receptor protects the Na+ channel from interaction with OETX but left it accessible to butanol.
Key wordsNerve membrane Na+ channel Batrachotoxin Oenanthotoxin Butanol
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