Stimulation of calcium accumulation in cardiac sarcolemma by protein kinase

Sarcolemmal membranes isolated from guinea pig heart ventricles contained an ATP-dependent calcium-sequestering activity. Sarcolemmal calcium accumulation but not binding was enhanced by preincubation of membranes with exogenous protein kinase, with cyclic AMP, or with isoproterenol. Protein kinase (EC 2.7.1.37) increased the V of Ca2+ accumulation by sarcolemma without any significant effect on the affinity for Ca2+. The endogenous protein kinase activity present in isolated sarcolemma affected membrane phosphorylation. Cyclic AMP increased the endogenous kinase activity modestly, whereas histone increased it significantly. Exogenous protein kinase also catalyzed phosphorylation of these membranes. Endogenous and exogenous kinase-catalyzed phosphorylation of sarcolemma was hydroxylamine-insensitive. Ca2+-dependent ATPase (EC 3.6.1.3) (extra ATPase) activity of sarcolemma was also increased by protein kinase.