Activity increases quantal size at the frog neuromuscular junction

Summary Two h of nerve stimulation at 10 Hz or of elevated spontaneous release in hypertonic solution increased the size of miniature end-plate potentials (m.e.p.p.'s) and currents at the frog neuromuscular junction, probably by increasing the amount of acetylcholine in a quantum. Increases in quantal size may modulate synaptic transmission.Acknowledgments. Supported by grant 10320 from the NINCDS and by a grant from the MDA. We are grateful to Dr I.S. Cohen for participating in some of the experiments and for helpful criticism, and to Drs C. Clausen and G. Baldo for help with the computer. Some of the results were presented at a meeting of the Physiological Society.