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

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.