Protein phosphatase-protein kinase interplay modulates α1b-adrenoceptor phosphorylation:: effects of okadaic acid

1 In the present work we studied the effect of protein phosphatase inhibitors on the phosphorylation state and function of alpha(1b)-adrenoceptors. 2 Okadaic acid increased receptor phosphorylation in a time- and concentration-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 noradrenaline-stimulated [S-35]GTP gamma S binding. Okadaic acid did not alter the noradrenaline-stimulated increases in intracellular calcium or the production of inositol trisphosphate. 5 Our data indicate that inhibition of protein phosphatases increases the phosphorylation state of alpha(1b)-adrenoceprors; this effect seems to involve protein kinase C. In spite of inducing all intense receptor phosphorylation, okadaic acid alters alpha(1b)-adrenergic actions to a much lesser extent than the direct activation of protein kinase C by phorbol myristate acetate.