Transmitter leakage from motor nerve endings

TLDR: 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, and it is calculated that such a steady leakage of ACh could exceed the efflux due to spontaneous quantal discharges by two orders of magnitude.

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 $\mu $V. The origin of this effect may be attributed to leakage of cytoplasmic acetylcholine (ACh) from nerve terminals, building up an ACh concentration of the order of 10$^{-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.