BRADYKININ INHIBITS ADENYLATE-CYCLASE ACTIVITY IN GUINEA-PIG ILEUM MEMBRANES VIA A SEPARATE HIGH-AFFINITY BRADYKININ B-2 RECEPTOR

In guinea pig ileum membranes, the pre-stimulated adenylate cyclase activity was dose-dependently inhibited by picomolar concentrations of bradykinin exhibiting an apparent IC,, value of approximately 30 pM. At nanomolar bradykinin concentrations (> 1 nM) this effect was attenuated. The inhibition of ileal adenylate cyclase was completely prevented by both the bradykinin B-2 receptor antagonist Hoe 140 (D-Arg[Hyp(3),Thi(5),D-Tic(7),Oic(8)]bradykinin) and pertussis toxin. The potency of bradykinin to inhibit ileal adenylate cyclase considerably correlates with a binding site with picomolar affinity for bradykinin. In addition, a second site was constantly found displaying nanomolar binding affinity for bradykinin. The occurrence of two independent bradykinin Bz receptors in guinea pig ileum membranes is further supported by three other lines of evidence: bradykinin stimulates [S-35]GTP[S] (guanosine 5'-O-[3-thiotriphosphate]) binding to guinea pig ileum membranes in a biphasic manner with EC(50) values which correspond to the affinities of both sites. In binding studies, the high-affinity site cannot be transformed into the low-affinity site in the presence of Gpp[NH]p (5'-guanylylimidodiphosphate). The specific binding of [H-3]bradykinin to guinea pig ileum membranes was also biphasically inhibited by increasing concentrations of Gpp[NH]p. Thus, our results favour the existence of two separate bradykinin B-2 receptors with different signal transduction pathways in guinea pig ileum membranes: one receptor with picomolar affinity for bradykinin which inhibits adenylate cyclase via a pertussis toxin-sensitive G protein of probably the G(i2) type and the other receptor with nanomolar affinity for bradykinin which might be responsible for bradykinin-induced stimulation of phosphoinositide hydrolysis.