Differences in the blocking action of benzocaine and amines on batrachotoxin-modified sodium channels of the Ranvier node

Abstract

Experiments by the voltage clamp method on Ranvier nodes of the frog nerve fiber showed that batrachotoxin sharply reduces the sensitivity of sodium channels to the blocking action of various tertiary (trimecaine, procaine, ajmaline, strychnine) and quaternary (QX-572, N-propylajmaline) amines but has no appreciable effect on blocking of sodium channels by neutral benzocaine. Inhibition of batrachotoxin-modified sodium currents by trimecaine is distinctly time-and potential-dependent in character. None of the amines tested gives rise to frequency-dependent (cumulative) blocking of the modified channels. Unblocking of these channels during rinsing of the node takes place much faster than unblocking of normal channels. The time course of recovery of the normal and modified currents after blocking by benzocaine is about the same. Relations between batrachotoxin "receptors" and the various blocking agents in the sodium channel are discussed.