[Antagonistic effects of acetylcholine and caffeine on the contractility of the auricular myocardium of rats].

In the rat atrium, the contraction rebound occurring after ACh treatment could not be related to an increase in action potential duration and disappeared in the presence of atropine or caffeine. Contractures elicited by caffeine (10 and 20 mM) were inhibited by ACh. This inhibition was suppressed by atropine. The hypothesis that ACh could increase the sarcoplasmic reticulum Ca diastolic reuptake is discussed.