The properties of the autonomically regulated chloride current (Icl) were studied in isolated guinea pig ventricular myocytes. This current was elicited upon exposure to isoproterenol (ISO) and reversed upon concurrent exposure to acetylcholine (ACh). Icl was time independent and exhibited outward rectification. The responses to ISO and ACh could be blocked by propranolol aald atropine, respectively, and Icl was also elicited by forskolin, 8-bromoadenosine 3',5'-cyclic monophosphate, and 3-isobutyl-l-methylxanthine, indicating that the current is regulated through a cAMP-dependent pathway. The reversal potential of the ISOinduced current followed the predicted chloride equilibrium potential, consistent with it being carried predominandy by Cl−. Activation of Icl produced changes in the resting membrane potential and action potential duration, which were C1− gradient dependent. These results indicate that under physiological conditions I o may play an important role in regulating action potential duration and resting membrane potential in mammalian cardiac myocytes. © 1990, Rockefeller University Press., All rights reserved.
