Inhibition of the veratridine-induced increase in cytosolic Ca 2+ and respiration by Ca 2+ antagonists in isolated cardiac myocytes

Abstract

1. 1. We studied the effect ofverapamil, nitrendipine, 3',4'-dichlorobenzamil (DCB) and Cd 2+ on the increase in cytosolic free Ca 2+ ([Ca 2+] c) and the rate of O 2-uptake induced by depolarization of isolated rat cardiac myocytes with veratridine. 2. 2. The degree of inhibition by the several drugs tested on the increase in [Ca 2+] c and respiration was dependent on extracellular Ca 2+, pH and Na +. 3. 3. Low verapamil and nitrendipine concentrations (2.5μM) were fully effective in Ca24″ channel blockade, as indicated from experiments with isoproterenol and in a low-Na + medium. 4. 4. A complete inhibition of veratridine-induced increase in [Ca 2+] c and O 2-uptake was attained with higher Ca 2+ blocker concentrations (25–30μM), implying that these processes depend to a major extent on some other Ca 2+ transport system, probably Na +/Ca 2+ exchange.