Effect of External Ca2+ on the Spontaneous and the Various Stimuli-Induced Acetylcholine Release from Guinea-Pig Ileum Myenteric Plexus

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Abstract
Effect of external Ca2+ concentration ([Ca2+]o) on spontaneous and various types of stimuli-induced acetylcholine (ACh) release from guinea-pig ileum myenteric plexus was studied. Electrical field stimulation- or high-K+-induced ACh release increased with the increment of [Ca2+]o. On the other hand, the spontaneous and the nicotine-induced ACh release increased up to 0.45 mM [Ca2+]o and then declined progressively as [Ca2+]o was raised. Oqualitatively similar results were obtained with dimethylphenylpirerazinium-, 5-hydroxytryptamine- and substance P-induced ACh release. These results were discussed in terms of the stabilizing effect of Ca2+.