Adrenaline and Failure of Neuromuscular Transmission

Abstract

IN the course of a study of the effects of adrenaline on neuromuscular transmission, we have observed repeatedly during tetanic stimulation of the rat diaphragm in vitro and gracilis in vivo failure of transmission of a type which has apparently received little or no attention in the literature. We recorded intracellular end-plate potentials by means of micropipettes filled with 3 M potassium chloride, which had an electrical impedance of 10–30 MΩ When the muscle nerve was stimulated repetitively with supramaximal shocks, the muscle spike potential disappeared as the rate of stimulation increased, leaving only a diminishing end-plate potential. Further increase of frequency, however, did not cause this potential to vanish gradually. Instead, failure of transmission occurred at a point which was evidently proximal to the end-plate. This failure was initially intermittent: certain impulses did not reach the end-plate and hence made no impression on the end-plate resting potential (sometimes activity from continuous fibres was seen because of electrical spread).