Phorbol Ester-induced Inhibition of the Beta-adrenergic System in Pulmonary Endothelium: Role of a Pertussis Toxin-sensitive Protein

To investigate possible cellular mechanisms for how activation of protein kinase C inhibits the relaxation caused by isoproterenol, we studied the effect of the protein kinase C activator 4α-phorbol-12β-myristate-13α-acetate (PMA) on the increase in cyclic AMP (cAMP) production and adenylate cyclase activity caused by isoproterenol in bovine pulmonary artery endothelial cells. Treatment of intact cells with PMA prevented in a time- and dose-dependent manner the increase in cAMP production caused by isoproterenol, whereas 4α-phorbol-12β-myristate-13α-acetate (4α-PMA), which does not activate protein kinase C, did not affect isoproterenol-induced cAMP production. PMA also reduced the increase in adenylate cyclase activity caused by isoproterenol, forskolin, and Gpp(NH)p. To test the hypothesis that the inhibitory effect of PMA is mediated via a pertussis toxin-sensitive G protein, we determined whether pretreatment of the cells with pertussis toxin would prevent the inhibitory effects of PMA. In pulmonary e...