Clumping and oscillations in evoked transmitter release at the frog neuromuscular junction.

1. Time series analysis of evoked transmitter release was performed at the frog neuromuscular synapse. 2. Clumping of end-plate potentials with similar amplitude was found in the time domain. 3. At low quantal contents periodic oscillations were observed with a period of 14 sec. 4. Clumping and oscillations are phenomena of presynaptic origin. 5. The results are explained on the hypothesis that periodic fluctuations occur in Ca concentration inside the presynaptic nerve terminal.