Effects of the phosphatase inhibitor calyculin A on the phosphorylation of C-protein in mammalian ventricular cardiomyocytes.

The effects of inhibitors of protein phosphatase activity on C-protein phosphorylation were studied in preparations from mammalian ventricles. Calyculin A (CyA), an inhibitor of type 1 and 2A protein phosphatases, was studied. CyA concentration- and time-dependency increased the phosphorylation state of C-protein in isolated 32P-labelled guinea pig ventricular cardiomyocytes. C-protein was identified by its reaction with a polyclonal antibody and immunoprecipitation. It is concluded that C-protein in intact cardiomyocytes could be a substrate for type 1 and 2A protein phosphatases.