The tachykinin NK 1 receptor antagonist, RP67580, inhibits the bradykinin-induced rise in intracellular Ca 2+ concentration in bovine pulmonary artery endothelial cells

Abstract

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.