Desensitization of the post-synaptic membrane of neuromuscular synapses induced by spontaneous quantum secretion of mediator.

Experiments on isolated frog neuromuscular junctions in voltage-clamped conditions demonstrated increases in the probability of spontaneous release of quanta of mediator, resulting in increases in the K+ ion concentration in the perfusion solution, and changes in the endplate miniature current amplitude induced by increased quantum generation were studied. Factors promoting the desensitization of the post-synaptic cholinergic membrane (inhibition of acetylcholinesterase and addition of proadifen) to levels greater than a certain (critical) frequency of endplate miniature current of the order of 50 spikes/sec were found to result in accumulation of activity and progressive reductions in the sensitivity of the post-synaptic membrane to the mediator acetylcholine.