CALCIUM-DEPENDENT ELECTROPHYSIOLOGICAL ALTERATIONS IN HYPERTROPHIED RAT CARDIOMYOCYTES

We compared the occurrence of calcium-dependent electrophysiological a lterations in left ventricular myocytes isolated from the heart of old spontaneously hypertensive (SHR) and age-matched normotensive Wistar Kyoto rats (WKY). Electrical and mechanical activity were measured in patch-clamped myocytes in which intracellular Ca2+ was allowed to chan ge freely. Ln parallel experiments, intracellular Ca2+ concentration w as monitored in fura-2-AM preloaded cells using an image analysis syst em. Left ventricular myocytes from SHR showed a significantly greater membrane capacitance (an index of cell size), a prolonged duration of the action potential and a higher incidence of delayed afterdepolariza tions (DADs) and associated aftercontractions, and of spontaneous acti vity. DADs were likely generated by intracellular Ca2+ waves due to sp ontaneous and local Ca2+ release from intracellular stores. These resu lts demonstate that DADs, possibly related to spontaneous intracellula r Ca2+ waves, occur frequently in hypertrophied rat cardiomyocytes and may be a relevant arrhythmogenic mechanism. (C) 1996 Academic Press, Inc.