SIGNAL-TRANSDUCTION PATHWAYS FOR B-1 AND B-2 BRADYKININ RECEPTORS IN BOVINE PULMONARY-ARTERY ENDOTHELIAL-CELLS

Bovine pulmonary artery endothelial (CPAE) cells respond to bradykinin , and it has been suggested that the receptors on these cells do not f all into the normal B-1/B-2 classification of bradykinin receptors [J. Pharmacol. Exp. Ther. 244:646-649 (1988)]. The present study describe s a detailed characterization of the subtypes of bradykinin receptors on CPAE cells. The B-1-selective agonist des-Arg(9)-bradykinin and the B-2-selective agonist bradykinin both activated polyphosphoinositide phospholipase C (PLC), caused an elevation in cytosolic Ca2+ concentra tion ([Ca2+](i)), and increased the rate of Ca-45(2+) efflux in CRAB c ells. The pharmacology of these responses was consistent with interact ions with B-1 and B-2 receptors. The effects of maximal concentrations of bradykinin and des-Arg(9)-bradykinin on the activity of PLC in pop ulations of cells were not additive, suggesting that the two subtypes were expressed on the same cells. Indeed, des-Arg(9)-bradykinin and br adykinin both evoked increases in [Ca2+](i) in 85% of single cells tes ted. The Ca2+ entry blocker NiCl2 inhibited bradykinin-induced increas es in [Ca2+](i) and Ca-45(2+) efflux. In contrast, NiCl2 did not inhib it the increase in Ca-45(2+) efflux evoked by des-Arg(9)-bradykinin an d induced oscillatory increases in [Ca2+](i) in response to the B-1 ag onist. NiCl2 had no effect on [H-3]inositol trisphosphate generation b y either agonist, indicating that its inhibitory effects on bradykinin -mediated Ca2+ responses were distal to B-2 receptor-induced activatio n of PLC. LaCl3, did not differentiate between the Ca-45(2+) efflux re sponses evoked by bradykinin and des-Arg(9)-bradykinin, attenuating bo th to a similar degree. Bradykinin-induced [H-3]inositol trisphosphate formation was desensitized after pretreatment with bradykinin, but th e response to des-Arg(9)-bradykinin was unchanged. Pretreatment with t he B-1 agonist did not inhibit responses evoked by subsequent challeng es with either des-Arg(9)-bradykinin or bradykinin. These results prov ide pharmacological evidence for the existence of two distinct bradyki nin receptor subtypes (B-1 and B-2) on CPAE cells, with no evidence fo r heterologous desensitization. Although both subtypes operated simila r signal transduction pathways, the Ca2+ responses evoked by the two r eceptors could be differentiated by NiCl2.