[Mediator secretion in the proximal and distal portions of a nerve ending of the sartorius muscle in the frog].

In experiments on neuromuscular preparations of the frog sartorius muscle the evoked transmitter release was investigated by extracellular recording. A decrease of the evoked transmitter release from proximal to distal parts of nerve terminals was observed related to a decrease in probability of transmitter quantum release. The terminal part of synapse showed smaller sensitivity to an increase in extracellular Ca2+ concentration as compared with the proximal part, smaller facilitation of transmitter release at double and repetitive stimulation, deeper and more quickly developing depression. A conclusion is made that these peculiarities of the transmitter release in the terminal parts of the synapse are due to smaller transmitter reserve and smaller permeability of the presynaptic membrane to Ca2+ ions.