The G Proteins of the Galphai and Galphaq Family Couple the Bradykinin Receptor to the Release of Endothelium-derived Relaxing Factor

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Bradykinin stimulates diverse functions in endothelial cells including the release of endothelium-derived relaxing factor (EDRF). Little is known, however, regarding the identity of the G protein(s) involved. Here we demonstrate that G proteins of the Galphai and Galphaq family are coupled to the bradykinin receptor (BKR) in bovine aortic endothelial cells by using specific antisera directed against the COOH-terminal region of Galphai2 (P4), Galphai3 (EC), and Galphaq (QL). These antisera are specific since their effects are blocked by the decapeptides from which they were derived. The degree of receptor-G protein coupling was assessed by the formation of high affinity agonist binding sites (HABS) and GTP hydrolysis. In a concentration-dependent manner, the QL antisera reduced HABS and GTPase activity by 65 and 60%, respectively, and effectively abolished them in membranes from pertussis toxin-treated cells. The combination of P4 and EC antisera produced a loss of HABS (41%) and GTPase activity (40%) comparable to the effects of pertussis toxin. These findings indicate that Galphai and Galphaq proteins mediate the cellular responses to bradykinin in bovine aortic endothelial cells and support the observation that bradykinin-stimulated EDRF release is relatively insensitive to pertussis toxin. (J. Clin. Invest. 1993. 92:2168-2172.) Key words: pertussis toxin. carboxy-terminus antisera. high affinity agonist binding sites. GTPase activity. Western Blotting

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