Biphasic effect of cardiac glycosides on action potential duration in isolated purkinje fibers

Abstract

Despite the historical use of cardiac glycosides, the data describing the electrophysiological characteristics of this class of drug are not fully clear. The present study reported the biphasic effect of cardiac glycosides, digoxin (1.25 μM) and acetylstrophanthidin (0.15 μM), on action potential duration in isolated Purkinje fibers by the conventional glass microelectrode technique. At the cycle lengths of 990, 690 and 490 msec., action potential duration lengthened within 10 min. and shortened after 10 min. of digoxin and acetylstrophanthidin administration. The biphasic effect was observed at a concentration of 4.0 mM [K+]o. However, at a higher [K+]o concentration of 5.4 mM, only the shortening effect on action potential duration was recorded. These results suggest that the biphasic effect of cardiac glycosides on action potential duration is related to the concentration of extracellular potassium and is not related to the stimulating cycle lengths.