Protein kinase C and phosphatase inhibitors block the ability of angiotensin I-converting enzyme inhibitors to resensitize the receptor to bradykininwithout altering the primary effects of bradykinin

Angiotensin I-converting enzyme (kininase II) inhibitors (ACEis) are very w idely used to treat cardiac conditions and nephropathies, but some of their beneficial activities cannot be attributed to enzyme inhibition alone. We investigated the effects of ACEis on the human bradykinin (BK) B-2 receptor expressed in Chinese hamster ovary cells transfected with the cDNA of huma n receptor and ACE, and on human pulmonary endothelial cells that constitut ively express both proteins. BK and its ACE-resistant peptide analog activa ted the B-2 receptor to release arachidonic acid and elevate [Ca2+](i) and subsequently desensitized it. The release of arachidonic by BK was independ ent of extracellular Ca2+. BK enhanced phosphorylation of the immunoprecipi tated B-2 receptor but enalaprilat significantly reduced it. ACEi resensiti zed the receptor by initiating a cross talk between the receptor and ACE. P rotein kinase C and phosphatase inhibitors distinguished the signaling by t he receptor when activated first by BK from BK acting on the resensitized r eceptor. Treatment of cells with 1 mu M calphostin, 100 nM staurosporine, 1 00 nM calyculin, or 500 nM okadaic acid did not affect either one of the pr imary actions of BK on the receptor. Protein kinase C or phosphatase inhibi tors, however, blocked the effects of BK on the receptor resensitized by en alaprilat or ramiprilat. The experiments clearly differentiate the primary activation of the receptor by BK from activation of the resensitized recept or after ACEi treatment. The existence of an intermediate component involve d in the action of ACEis to enhance release of vasoactive mediators by BK i s suggested.