The tachykinin NK1 receptor antagonist, RP67580, inhibits the bradykinin-induced rise in intracellular Ca2+ concentration in bovine pulmonary artery endothelial cells

The bradykinin-induced rise in intracellular Ca 2+ concentration ([Ca 2+ ] i ) and the bradykinin receptor involved in this response were characterized in bovine pulmonary artery endothelial cells. It was found that bradykinin induces an intracellular biphasic Ca 2+ response, consisting of a transient peak followed by an elevated plateau phase. Both bradykinin and the bradykinin B 1 receptor agonist, des-Arg 9 -bradykinin, induced a concentration-dependent increase in [Ca 2+ ] i , but the bradykinin-induced rise was much greater. Moreover, the bradykinin-induced [Ca 2+ ] i rise could be inhibited by the bradykinin B 2 receptor antagonists, d -Arg 0 [Hyp 3 , Thi 5,8 , d -Phe 7 ]bradykinin and Hoe 140 ( d -Arg[Hyp 3 , Thi 5 , d -Tic 7 , Oic 8 ]bradykinin), but not by the bradykinin B 1 receptor antagonist, des-Arg 9 -[Leu 8 ]bradykinin. From these results it can be concluded that a bradykinin B 2 receptor is involved in this response. Furthermore, we found that the tachykinin NK 1 receptor antagonist, RP67580 ([imino 1 (methoxy-2-phenyl)-2 ethyl]-2 diphenyl 7,7 perhydroisoindolone-4 (3aR, 7aR)), and its negative enantiomer, RP68651 (2-[1-imino 2-(2 methoxy phenyl) ethyl] 7,7 diphenyl 4-perhydroisoindolone (3aS–7aS)), could inhibit the bradykinin-induced [Ca 2+ ] i response, although no functional tachykinin NK 1 receptors were found. Binding studies evidenced no binding of RP67580 or RP68651 to the bradykinin receptor. We conclude that RP67580 inhibits the bradykinin-induced rise in [Ca 2+ ] i via a bradykinin B 2 receptor-independent mechanism.