The effect of magnesium on the time course of facilitation at the crayfish neuromuscular junction.

Abstract Synaptic currents (EPSCs) were recorded extracellularly from single junctions. Pairs of EPSCs were elicited at different intervals, the increase of amplitude of the second one indicating facilitation. Elevated Mg concentrations reduced the amplitude of the EPSC and prolonged facilitation. Also, if the amplitude of the EPSCs at high Mg is made the same as in the control, by raising [Ca] 0 , facilitation is still prolonged. It is concluded that Mg inhibits not only the entry of Ca into the nerve terminal but also its removal.