Batrachotoxin protects sodium channels from the blocking action of oenanthotoxin

Abstract

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.