Subject(s)
Calcium Signaling/physiology , Calcium/pharmacokinetics , Carbachol/pharmacology , Neuromuscular Junction/physiology , Receptors, Cholinergic/metabolism , Receptors, Presynaptic/physiology , Synaptic Transmission/physiology , Animals , Calcium/metabolism , Calcium Signaling/drug effects , Cholinergic Agonists/pharmacology , In Vitro Techniques , Rana ridibundaABSTRACT
The effects of calcium on the quantal content of nerve-evoked endplate currents (EPC) and on the temporal parameters of quantal release were studied in the frog neuromuscular synapse using the method of "subtractions". It was shown that under physiological conditions quanta generating multiquantal postsynaptic responses were released nonsynchronously because of a considerable variability of latencies of the uniquantal responses forming multiquantal EPC. Different calcium dependences for EPCs quantal content and time course of the quantal release were revealed. The average quantal content grew exponentially with the increase in calcium concentration from 0.4 to 1.8 mmol/L, whereas the release synchronicity reached the maximum at 1 mmol/L calcium. It was suggested that the changes in the synchronicity of the evoked release were one of the mechanisms of the synaptic plasticity.