[Differences in the blocking action of benzocaine and amino compounds on batrachotoxin-modified node of Ranvier sodium channels].

Voltage-clamp experiments on the frog Ranvier node have shown that batrachotoxin (BTX) decreases drastically the sensitivity of sodium channels to the blocking action of various tertiary (procaine, trimecaine, ajmalin, strychnine) and quaternary (QX-572, N-propylajmaline) amine drugs but does not affect noticeably sodium channels blockade produced by neutral benzocaine. The inhibition of BTX-modified sodium current by large concentrations of trimecaine (3.5 mM) is time- and voltage-dependent. Neither of the amines used proved to be able to cause frequency-dependent (cummulative) block of modified channels. Unblocking of these channels during washing of the node with Ringer solution proceeds much faster than that of normal channels. On the contrary, restoration of normal and modified currents blocked previously by benzocaine has the same time course. The relationships between "receptors" for BTX and various sodium channel blockers are discussed.