Dual action of maltoxin, a neuromuscular blocking agent from malt rootlet

Abstract

Maltoxin, an amine obtained from brew malt rootlet, causes a neuromuscular block in the frog. Its mode of action on the frog's sartorius muscle has been studied mainly with the aid of intracellular microelectrodes. Maltoxin of 10–5 concentration caused an over-all depolarization of the muscle fibers; therefore, direct and indirect stimulations of the muscle were ineffective in producing muscle action potential. Progressive repolarization took place thereafter and the muscle became excitable by direct stimulation, though indirect stimulation remained ineffective for a long period of time. Small end-plate potentials observed could not be explained in terms of depolarization. It was found that the sensitivity of the end-plate membrane to acetylcholine was effectively depressed by maltoxin, and that this is responsible for the persistent neuromuscular block. The initial over-all depolarization caused by maltoxin was fairly antagonized by a previous treatment with d-tubocurarine. It is concluded that maltoxin has a dual mode of action, having some resemblance to acetylcholine, decamethonium, succinylcholine and nicotine.