title: Effect of acetylcholine on calcium efflux from atrial myocardium.
abstract: The effect of acetylcholine (ACh) on the efflux of 45Ca from atrial myocardial tissue was studied on left guinea-pig auricles. ACh at concentrations of 10(-7)-10(-6) g/ml abolished the twitch responses and caused development of week transient contracture in non-stimulated preparations. The extracellular space (ECS) was not affected. ACh at concentrations of 10(-8)-10(-6) g/ml increased 45Ca efflux from quiescent preparations in a dose-dependent manner. This effect was antagonized by atropine. The contracture developed in Ca2+, Na+-free medium was further enhanced by ACh at concentrations of 10(-7)-10(-6) g/ml. These results suggest that ACh causes the release of calcium from atrial tissue. This effect may contribute to the mechanism of the negative inotropic action of ACh.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*
chemical_list: D000109:Acetylcholine; D002118:Calcium