A dual effect of calcium ions on neuromuscular facilitation

Abstract

The changes in neuromuscular facilitation produced by varying extracellular Ca and Mg concentrations were studied at the frog neuromuscular junction using intracellular recording and automatic averaging of responses. When [Ca] was elevated 3 effects were observed a large increase in transmitter release by the first impulse; adecrease in facilitation at short intervals between impulses; and a prolongation of the time course of the facilitated release. If the release by the first impulse is kept at constant level, by raising both [Ca] and [Mg], facilitation becomes greater at all impulse intervals. The results were discussed in terms of the hypothesis that the action of Ca is responsible for neuromuscular facilitation.