Enhancement of Bradykinin and Resensitization of Its B 2 Receptor

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Abstract
—We studied the enhancement of the effects of bradykinin B 2 receptor agonists by agents that react with active centers of angiotensin-converting enzyme (ACE) independent of enzymatic inactivation. The potentiation and the desensitization and resensitization of B 2 receptor were assessed by measuring [ 3 H]arachidonic acid release and [Ca 2+ ] i mobilization in Chinese hamster ovary cells transfected to express human ACE and B 2 receptor, or in endothelial cells with constitutively expressed ACE and receptor. Administration of bradykinin or its ACE-resistant analogue desensitized the receptor, but it was resensitized (arachidonic acid release or [Ca 2+ ] i mobilization) by agents such as enalaprilat (1 μmol/L). Enalaprilat was inactive in the absence of ACE expression. La 3+ (100 μmol/L) inhibited the apparent resensitization, probably by blocking the entry of extracellular calcium. Enalaprilat resensitized the receptor via ACE to release arachidonic acid by bradykinin at a lower concentration (5 nmol/L) than required to mobilize [Ca 2+ ] i (1 μmol/L). Monoclonal antibodies inhibiting the ACE N-domain active center and polyclonal antiserum potentiated bradykinin. The snake venom peptide BPP5a and metabolites of angiotensin and bradykinin (angiotensin-[1–9], angiotensin-[1–7], bradykinin-[1–8]; 1 μmol/L) enhanced arachidonic acid release by bradykinin. Angiotensin-(1–9) and -(1–7) also resensitized the receptor. Enalaprilat potentiated the bradykinin effect in cells expressing a mutant ACE with a single N-domain active site. Agents that reacted with a single active site, on the N-domain or on the C-domain, potentiated bradykinin not by blocking its inactivation but by inducing crosstalk between ACE and the receptor. Enalaprilat enhanced signaling via ACE by Gα i in lower concentration than by Gα q -coupled receptor.