Transmitter leakage from motor nerve endings

Abstract

When endplates of anti-esterase treated frog muscle are subjected to a massive ionophoretic dose of curare, a small local hyperpolarization is recorded in many fibres, amounting on the average to about 40 μV. The origin of this effect may be attributed to leakage of cytoplasmic acetylcholine (ACh) from nerve terminals, building up an ACh concentration of the order of 10 -8 M in the synaptic cleft and causing a minute steady depolarization of the endplate. It is calculated that such a steady leakage of ACh, although producing a barely detectable electrical effect, could exceed the efflux due to spontaneous quantal discharges by two orders of magnitude, and account for the assayed amounts of ACh release from resting muscle.