On the mechanism by which calcium and magnesium affect the release of transmitter by nerve impulses

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Abstract
The relationship between the quantal content of end-plate potentials (epps) and the bathing [Ca] and [Mg] was determined at neuromuscular junctions in the rat diaphragm in vitro. Epps were recorded intracellularly from preparations exposed to solutions with [Ca] between 0.05 and 10 m[image]. and [Mg] between 0.1 and 12.5 m[image]. The quantal content of epps was increased by raising the [Ca] over this range and decreased by raising the [Mg]. There appeared to be competition of Mg with Ca at 3 sites in the nerve terminal membrane. The kinetic scheme based on competition of Ca and Mg at 3 sites could quantitatively explain the effects of Ca and Mg upon the quantal content of epps and also the effects of these ions upon miniature endplate potential frequency.