[Effects of praeruptorin-C on cytosolic free calcium in cultured rat heart cells].

The negative inotropic effect of Pra-C was supposed to be related to the blocking of extracellular calcium influx but direct evidence is not known. We, therefore, examined the effects of Pra-C on [Ca2+]i in isolated rat ventricular myocytes using the fluorescent Ca(2+)-indicator Fura-2/AM. It was found that Pra-C inhibited the elevation of [Ca2+]i induced by potassium-depolarization, high extracellular calcium and calcium agonist Bay K 8644 in a dose-dependent manner. At 1.0 mumol.L-1, it decreased the [Ca2+]i at the presence of 75 mmol.L-1 KCl, 10 mol.L-1 CaCl and 3 mumol.L-1 Bay K 8644 by 50, 31 and 42% respectively. No significant effect on ouabain evoked [Ca2+]i increase was found, showing that it does not affect sarcolemmal Na(+)-Ca2+ exchange. These results further indicate that Pra-C may decrease the [Ca2+]i of myocyte by blocking voltage-dependent calcium channels.