Correlation Between Amplitudes and Rise Times of the Miniature Endplate Potentials in Frog Muscle

Abstract

An investigation of the relationship between the amplitudes and rise times of the miniature end-plate potentials recorded from the neuromuscular junctions of the frog sartorius has shown the existence of a positive correlation between these two parameters. This finding is consistent with the occurrence of a process of “spreading activation”, i.e. the progressive recruitment of end-plate receptors by a wave of acetylcholine molecules diffusing tangentially within the synaptic space. It appears that the initial concentration of transmitter molecules within the synaptic cleft must be large enough to saturate the receptors of the end-plate membrane, immediately subjacent to the site of release. This idea is supported by the result of calculations using a highly simplified model of the myoneural junction.