[Polymodality of the distribution of synaptic delays in the neuromuscular junctions of the frog].

Measurements of the synaptic delay of uniquantal responses have been made on frog cutaneous pectoris muscle. Extracellular focal recording and low mean quantal content (0.05-1) was used. The distribution of delays obtained had a polymodal character with the mean modal interval equal to 0.22 +/- 0.01 ms (n = 13). An increase of the quantal content induced only a redistribution of the mode weights, but the modal interval did not change. A decrease in the temperature induced an increase in the modal interval with the temperature coefficient Q10 = 2.42 +/- 0.14 (n = 15). According to the hypothesis which was used for explaining the data obtained, the process of transmitter quanta release is determined by interaction of two molecular mechanisms: an increase of the release probability depending on the intracellular calcium concentration; rhythmical work of the mechanism realizing the quantum release. The latter does not depend on the calcium concentration but depends on temperature. The polymodal distribution of synaptic delays reflects this rhythmical work of each presynaptic active zone.