Differences in the effect of metabolic inhibition on action potentials and calcium currents in endocardial and epicardial cells.

BACKGROUNDIschemia-induced electrophysiological changes are more prominent in epicardial cells than in endocardial cells. Epicardial action potentials shorten more than endocardial action potentials during ischemia. Since the L-type Ca2+ current plays an important role in the maintenance of action potential duration, we hypothesized that the Ca2+ current is affected more in epicardial cells than in endocardial cells during ischemia.METHODS AND RESULTSTo test this hypothesis, we examined the effect of metabolic inhibition, a major component of ischemia, on action potentials and the Ca2+ current in single cells isolated from the endocardial and epicardial layers of the feline left ventricle. The membrane voltage and current were measured by using the whole-cell mode of the patch-clamp technique. During control periods, action potentials recorded from epicardial myocytes had lower amplitude, a prominent notch between phases 1 and 2, and shorter action potential duration compared with those recorded from endo...