MODULATION BY ACETYLCHOLINE OF THE ELECTRICALLY‐EVOKED RELEASE OF [3H]‐ACETYLCHOLINE FROM THE ILEUM OF THE GUINEA‐PIG

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Abstract
1 Acetylcholine (ACh) stores within neurones of the myenteric plexus of the guinea-pig were labelled with [3H]-choline and the influence of unlabelled ACh, atropine, or atropine and unlabelled ACh on the electrically-evoked output of [3H]-ACh was evaluated. 2 Electrical transmural stimulation (5 Hz) of the ileum led to an increase in the output of [3H]-ACh over that released spontaneously. Superfusion with unlabelled ACh (6.8 μm) caused a marked reduction in the release of [3H]-ACh which was reversed by atropine (3.5 μm). Atropine itself had no effect on the electrically-evoked [3H]-ACh. 3 These experiments provide further evidence for the existence in the guinea-pig ileum of neuronal muscarinic receptors for ACh subserving an inhibitory role on transmitter release.