[Characteristics of the time course of miniature endplate currents in different parts of the neuromuscular junction in the frog].

Extracellular glass microelectrodes were used for recording miniature endplate currents (MEPC) from proximal and distal parts of frog sartorius synapse. The amplitude and half-time of decay (t1/2) of MEPC in proximal parts exceeded those in distal parts. These differences were eliminated by tubocurarine and increased under the influence of armin. In 80% of experiments the positive correlation between the amplitude and t1/2 of MEPC was revealed, which reflects repetitive binding of acetylcholine (ACh) molecules with cholinoreceptors (ChR). Positive correlation was observed in all investigated proximal parts of terminal, and only in half of distal ones. The electron microscopic study showed that postsynaptic folds in proximal parts occur more frequently, are poorly branching and rather shallow. A conclusion is made that the more prolonged time course of MEPC in proximal synapse parts is due to the more pronounced repetitive binding of ACh molecules with ChR of the postsynaptic membrane, which may be explained by high density of ChR and special, features of the synaptic cleft geometry in proximal parts.