Characterization of acetylcholine release from insect synaptosomes

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Abstract

Synaptosomes prepared from ganglia of Locusta migratoria, are able to accumulate [3H]choline and convert most of it to acetylcholine. Exposure of the labelled synaptosomes to media containing elevated K+ concentrations evoked a large increase in the efflux of tritiated acetylcholine. Some characteristics of acetylcholine release from insect nerve terminals were studied by continously perfusing synaptosomes with various solutions. Depolarization of the nerve endings with veratridine or K+ induced a release which was dependent on extracellular calcium, whereas Mg2+ inhibited the release. Pretreatment with the Ca2+-ionophore, A 23187, allowed a calcium-induced release under non-depolarizing conditions. The calcium-dependent efflux is thought to reflect stimulus-secretion coupling processes. In the presence of eserine and carbamylcholine the release was inhibited. Analysis of various cholinergic drugs revealed that the evoked efflux was susceptible to muscarinic ligands, it was enhanced by atropine and reduced by oxotremorine. The results suggest a feed-back regulation of acetylcholine release via muscarinic autoreceptors.

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