Protein phosphatase-protein kinase interplay modulates alpha(1b)-adrenoceptor phosphorylation: effects of okadaic acid

1 In the present work we studied the effect of protein phosphatase inhibito rs on the phosphorylation state and function of alpha(1b)-adrenoceptors. 2 Okadaic acid increased receptor phosphorylation in a time- and concentrat ion-dependent fashion (maximum at 30 min, EC50 of 30 nM). Other inhibitors of protein phosphatases (calyculin A, tautomycin and cypermethrin) mimicked this effect. 3 Staurosporine and Ro 31-8220. inhibitors of protein kinase C. blocked the effect of okadaic acid on receptor phosphorylation. Neither genistein nor wortmannin altered the effect of okadaic acid. 4 The intense adrenoceptor phosphorylation induced by okadaic acid altered the adrenoceptor-G protein coupling, as evidenced by a small decreased nora drenaline-stimulated [S-35]GTP gamma S binding. Okadaic acid did not alter the noradrenaline-stimulated increases in intracellular calcium or the prod uction of inositol trisphosphate. 5 Our data indicate that inhibition of protein phosphatases increases the p hosphorylation state of alpha(1b)-adrenoceprors; this effect seems to invol ve protein kinase C. In spite of inducing all intense receptor phosphorylat ion, okadaic acid alters alpha(1b)-adrenergic actions to a much lesser exte nt than the direct activation of protein kinase C by phorbol myristate acet ate.