HUMAN VASCULAR KININ RECEPTORS OF THE B-2 TYPE CHARACTERIZED BY RADIOLIGAND BINDING

1 The human umbilical vein responds to bradykinin (BK) with contractio ns that are mediated by B-2 receptors. In the present study. the corre sponding vascular smooth muscle B-2 binding sites have been investigat ed. 2 [H-3]-BK, a full agonist labelled ligand, was used to demonstrat e a single binding site giving a K-d value of 0.51 +/- 0.02 nM and a B -max of 24 +/- 1 fmol mg(-1) protein. Scatchard plots were linear (r = 0.98) in the 0.05-5 nM range of concentrations. Non-specific binding was found to be 30% of total binding. 3 Competition binding curves gav e the following order of potency for various B-2 receptor agonists: BK -[Hyp(3)]-BK greater than or equal to Lys-BK much greater than[Aib(7)] -BK>>>[desArg(9)]-BK, which is typical of B-2 receptors. There was no binding to B-1 receptors since the selective B-1 receptor ligand, Lys- [desArg(9)]BK was inactive up to 10 mu M (n=4). 4 Characterization of the binding site with antagonists, performed with three chemically dis tinct series of peptide and non-peptide compounds, revealed a high aff inity of Hoe 140 (D-Arg-[Hyp(3),Thi(5),D-Tic(7),Oic(8)]-BK) (K-i 0.17 nM; n=4) which was more potent that FR 173657 nyl)oxymethyl]phenyl]-N- methylaminocarbonylmethyl] acrylamide]) (K-i 1.94 nM; n=4), D-Arg-[Hyp (3),D-Phe(7),Leu(8)]-BK (K-i 256 nM; n=4) and Win 64338 (phosphonium, halenyl)-1-oxopropyl]amino]phenyl]methyl]tributyl, chloride, monohydro chloride) (K-i 1,450 nM; n=4). 5 The present study describes and chara cterises B-2 receptor binding sites in the vascular smooth muscle of t he human umbilical vein. The binding assay appears to be suitable for studying new agonists or antagonists designed to activate or block the B-2 receptor class that mediate the majority of the physiopathologica l effects of kinins in man.