A voltage‐clamp study of the permeability change induced by quanta of transmitter at the mouse end‐plate.

Abstract

Miniature end-plate currents (m.e.p.c.) were recorded from mouse diaphragm using a point voltage-clamp. The relation between m.e.p.c. amplitude and membrane potential was determined in bathing solutions of varied composition. The permeability change associated with generation of the m.e.p.c. (i.e., evoked by a quantum of transmitter) apparently corresponds to the opening of a single species of membrane channel that allows the free movement of K+, Na+, NH4+ and Li+ ions along their electrochemical gradients. The channel discriminates little between these ions. The apparent order of permeability is Li+ > NH4+ > Na+ .gtoreq. K+. The apparent permeability per channel corresponds to that expected for channels of about 6.4 .ANG. diameter, 100 .ANG. length and ionic mobility the same as in dilute solution.