Katz_1973_J.Physiol.London_231_549

Acetylcholine (ACh) noise and miniature end-plate potentials were recorded with focal external microelectrodes. The effect of prostigmine on the time course of the mol. and quantal transmitter actions wasstudied. Prostigmine (10-6 g/ml) had little or no effect on the duration of the mol. gating action, while it greatly prolonged the quantal conductance change. After inhibition of ACh hydrolysis, the removal of the transmitter from the synapse was generally too slow to be accounted for by free diffusion. Apparently, diffusion is delayed by binding to postsynaptic receptors. This is consistent with the finding that receptor blockage by curare or .alpha.-bungarotoxin shortens as well as reduces quantal transmitter action. The correlated effects of the receptor-blocking agents, on size and time course of the miniature end-plate currents, were subjected to a simple anal. Its result suggests that after inhibition of cholinesterase .apprx.2/3 of the quantal packet of ACh combines with post-synaptic receptors. During focal external recording the effect of prostigmine on the time course of miniature end-plate potentials can become exaggerated due to what appears to be a compression artifact which obstructs outward diffusion of the transmitter.