[Periodic changes in evoked mediator secretion at the neuromuscular synapse].

Extra- and intracellular recordings of the frog m. sartorius postsynaptic potentials with low concentration of Ca2+ ions (0.2-0.6 mmol/l) aided to study the dynamics of quanta transmitter release in prolonged motor nerve stimulation (0.5-10.0 imp/s). The statistical analysis showed that with intracellular recording only, time intervals between transmitter release were distributed in an evenly manner. Estimation of the correlation function and the spectral density revealed the periodical fluctuations of evoked transmitter release with periods from a few seconds to 1-2 min. With intracellular recording, oscillations of the transmitter release occurred in about 1/3 of cases whereas with extracellular recording they were always present. Analyses of a single release site activity by means of two extracellular electrodes inserted into a single nerve terminal, showed considerable changes of the cyclic transmitter secretion. The evoked transmitter release in a single release site seems to fluctuate periodically.