[Effect of cyproheptadine on Ca2+,Mg(2+)-ATPase activities and 45Ca2+ uptake function in canine myocardial...

The effects of cyproheptadine on Ca2+,Mg(2+)-ATPase activities and 45Ca2+ uptake function in isolated canine myocardial sarcoplasmic reticulum were studied. Cyproheptadine at concentrations of 8 x 10(-6) mol/L-2 x 10(-4) mol/L showed hardly any influence on Ca2+,Mg(2+)-ATPase activities of the myocardial sarcoplasmic reticulum in canine, but inhibited the enzyme activities (rate of inhibition: 39.85%, P < 0.01) at the concentration of 10(-3) mol/L. The myocardial sarcoplasmic reticulum was shown to take up 45Ca2+ significantly in a time-dependent manner and the 45Ca2+ uptake was 312.79 +/- 22.25 nmol/mg protein at 30 min. Cyproheptadine was found to inhibit the Ca2+ uptake of sarcoplasmic reticulum with an IC50 of 1.94 x 10(-4) mol/L.