Cyclic AMP‐dependent phosphorylation of a 16 kDa protein in a plasma membrane‐enriched fraction of rat aortic myocytes

Abstract
Phosphorylation induced by cAMP-dependent protein kinase was examined in a plasma membrane-enriched fraction from control and β-adrenergic-stimulated rat aortic myocytes. Phosphorylation of a 16 kDa protein which copurified with the plasma membrane marker (Na++K+)-ATPase was most prominent. It was decreased by pretreatment of the myocytes with isoproterenol and the effect of isoproterenol was inhibited by propranolol. Both phosphorylation induced by cAMP-dependent protein kinase and its inhibition by isoproterenol pretreatment declined in preparations exposed to endogenous phosphatase. These results provide strong evidence that β-adrenergic stimulation of aortic myocytes induces in situ phosphorylation of a 16 kDa plasma membrane protein.