[Phenomenon of asynchrony of induced mediator release at the neuromuscular junction of the frog].

"Hump-like" distortions of evoked end-plate currents were observed with the help of extracellular focal recordings in sartorius and cutaneous frog muscle preparations at 20 degrees C. These distortions resembled spontaneous or unitary evoked responses by their amplitude and time course. Statistical analysis allowed rejecting the simplified assumption that these "humps" were the result of spontaneous nervous signals superimposed on the evoked ones. The asynchronous release of single quanta forming the multiquantal response seemed to be a more plausible explanation. A distinct correlation between the distribution of synaptic delay values of unitary responses (at low quantal content) and observed asynchronous responses (at high quantal content) was found. A polymodal pattern of distribution of synaptic delays was shown in both cases. It is concluded that the presence of asynchronous responses and discrete character of variations in synaptic delays are an intrinsic property of the transmitter release mechanism.