Cardiac hypertrophy determines digitalis action on intracellular Ca2+ in human myocardium

Ventricular hypertrophy alters transporters associated with digitalis action, but the outcome of digitalis treatment on intracellular cations in the hypertrophied human myocardium remains unknown. Using double-barreled Ca2+-selective microelectrodes, we simultaneously measured Ca2+ activity and membrane potential in myocardial samples from patients without and with ventricular hypertrophy, prior to and following exposure to strophanthidin, a prototype digitalis. We found that ventricular hypertrophy is associated with greater strophanthidin-induced increase in diastolic Ca2+ levels compared to that observed in the absence of hypertrophy. Furthermore, in hypertrophied myocardium the magnitude of the increase in Ca2+ induced by strophanthidin was inversely related to increase in myocardial mass. Thus, the extent of ventricular hypertrophy determines digitalis action on intracellular Ca2+ within the human myocardium. (C) 1997 Elsevier Science B.V.