Motor End-Plate Differences as a Determining Factor in the Mode of Action of Neuro-Muscular Blocking Substances

Abstract

IN consequence of the results obtained with decamethonium in the cat^1,2 and in human beings³, we felt justified in putting forward the thesis that decamethonium produced a neuromuscular block in mammals only through a persisting depolarization of the motor end-plate. But work undertaken with other mammalian species (monkeys, dogs, hares) during the past few months reveals that decamethonium can produce in these three a neuromuscular block which differs in many ways from the block produced by pure depolarization. Thus in these species the tetanus is poorly sustained, and antagonizes the block, which is also antagonized by anticholinesterases. The white muscles show an acute decreasing sensitivity to decamethonium, a second injection of a dose which at first produced almost complete paralysis failing to produce any effect. If one records simultaneously from a red muscle and a white one⁴, a transition from a depolarizing type of block to a block by competitive inhibition is seen.