[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 PraC on [Ca~(2+)] 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 [Ca~(2+)]i induced by potassiumdepolarization, high extracellular calcium and calcium agonist Bay K 8644 in a dose-dependent manner. At 1.0 μmol · L~(-1), it decreased the [Ca~(2+)]i at the presence of 75 mmol · L~(-1) KCl, 10 mol · L~~(-1) CaCl and 3 μmol · L~(-1) Bay K 8644 by 50, 31 and 42% respectively. No significant effect on ouabain evoked [Ca~(2+)]i increase was found, showing that it does not affect sarcolemmal Na~+ —Ca~(2+)exchange. These results further indicate that Pra-C may decrease the [Ca~(2+)]i of myocyte by blocking voltage-dependent calcium channels.