Enhancement of bradykinin and resensitization of its B-2 receptor

We studied the enhancement of the effects of bradykinin B-2 receptor agonis ts by agents that react with active centers of angiotensin-converting enzym e (ACE) independent of enzymatic inactivation. The potentiation and the des ensitization and resensitization of B-2 receptor were assessed by measuring [H-3]arachidonic acid release and [Ca2+](i) mobilization in Chinese hamste r ovary cells transfected to express human ACE and B-2 receptor, or in endo thelial cells with constitutively expressed ACE and receptor. Administratio n of bradykinin or its ACE-resistant analogue desensitized the receptor, bu t it was resensitized (arachidonic acid release or [Ca2+](i) mobilization) by agents such as enalaprilat (1 mu mol/L). Enalaprilat was inactive in the absence of ACE expression. La3+ (100 mu mol/L) inhibited the apparent rese nsitization, probably by blocking the entry of extracellular calcium. Enala prilat resensitized the receptor via ACE to release arachidonic acid by bra dykinin at a lower concentration (5 nmol/L) than required to mobilize [Ca2](i) (1 mu mol/L). Monoclonal antibodies inhibiting the ACE N-domain active center and polyclonal antiserum potentiated bradykinin. The snake venom pe ptide BPP5a and metabolites of angiotensin and bradykinin (angiotensin-[1-9 ], angiotensin-[1-7], bradykinin-[1-8]; 1 mu mol/L) enhanced arachidonic ac id release by bradykinin. Angiotensin-(1-9) and -(1-7) also resensitized th e receptor. Enalaprilat potentiated the bradykinin effect in cells expressi ng a mutant ACE with a single N-domain active site. Agents that reacted wit h a single active site, on the N-domain or on the C-domain, potentiated bra dykinin not by blocking its inactivation but by inducing crosstalk between ACE and the receptor. Enalaprilat enhanced signaling via ACE by G alpha(i) in lower concentration than by G alpha(q)-coupled receptor.