The influence of quantal content on the time course of the endplate current in frogs

The aim of this study was to find out whether control and facilitated endplate current (EPC) of a curarized frog nerve-muscle preparation stimulated with paired impulses decay at the same time constant. The experiments revealed that the decay of the greater second EPC was slower in nearly half of the cases. This half of the results suggests that a larger quantity of the released transmitter and, consequently, a higher density of open channels promote a cooperative effect among them. The end effect can be a longer mean lifetime of open acetylcholine channels. In the other half of the experiments, the mean lifetime of open channels seems to be independent of the agonist concentration.