Protein kinase C and phosphatase inhibitors block the ability of angiotensin I-converting enzyme inhibitors to resensitize the receptor to bradykinin without altering the primary effects of bradykinin.

Angiotensin I-converting enzyme (kininase II) inhibitors (ACEis) are very widely 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 human receptor and ACE, and on human pulmonary endothelial cells that constitutively express both proteins. BK and its ACE-resistant peptide analog activated the B(2) receptor to release arachidonic acid and elevate [Ca(2+)](i) and subsequently desensitized it. The release of arachidonic by BK was independent of extracellular Ca(2+). BK enhanced phosphorylation of the immunoprecipitated B(2) receptor but enalaprilat significantly reduced it. ACEi resensitized the receptor by initiating a cross talk between the receptor and ACE. Protein kinase C and phosphatase inhibitors distinguished the signaling by the receptor when activated first by BK from BK acting on the resensitized receptor. Treatment of cells with 1 microM calphostin, 100 nM staurosporine, 100 nM calyculin, or 500 nM okadaic acid did not affect either one of the primary actions of BK on the receptor. Protein kinase C or phosphatase inhibitors, however, blocked the effects of BK on the receptor resensitized by enalaprilat or ramiprilat. The experiments clearly differentiate the primary activation of the receptor by BK from activation of the resensitized receptor after ACEi treatment. The existence of an intermediate component involved in the action of ACEis to enhance release of vasoactive mediators by BK is suggested.