[The characteristics of the action of calcium ions on miniature end-plate currents after the disruption of mediator hydrolysis]

Abstract

Effect of calcium on the miniature end-plate currents (MEPC) at the frog neuromuscular junction was studied by the voltage-clamp technique. Rise of the calcium concentration in the Ringer solution up to 9 mmol/l caused a decrease of the MEPC amplitude which was related to the reduction of the end-plate channel conductance. Calcium had no effect on the time course of MEPCs at the active acetylcholinesterase (AChE) but accelerated MEPC decay by 26% after AChE inhibition by neostigmin or armin. It is supposed that the shortening effect of calcium on the MEPC decay phase is based on the ability of calcium to modulate the block of ionic channels by acetylcholine or to accelerate the process of desensitization of the postsynaptic membrane.