[Effect of muscle fiber activity on mediator release at frog neuromuscular synapses]

Direct stimulation of muscle, in addition to nerve stimulation, significantly augments the EPP facilitation in the frog neuro-muscular preparation. The mean amplitude of the miniature potentials does not change, at that, which suggests presynaptic nature of the effect. The effect of muscle activity on the quantum content of facilitated EPPs increases with increasing of the stimulation frequency. This suggests that the additional EPP facilitation is due to the electrical rather than mechanical activity of muscular fibers. Experiments with testing EPP delayed for different time intervals after rhythmic stimulation, suggest that acitvity of muscular fibers enhances the probability of trnasmitter release by the presynaptic AP during rhythmic stimulation. The process of transmitter accumulation must simultaneously accelerate. Possible mechanisms of feedback effect of the muscular fibers activity on the state of presynaptic terminals, are discussed.