Cloning and functional characterization of the ornithokinin receptor - Recognition of the major kinin receptor antagonist, HOE140, as a full agonist

Kinins are proinflammatory peptides that dilate vessels, increase vascular permeability, contract smooth muscles, and provoke pain, The known mammalian kinin receptors are classified as two subtypes, i.e. the B1 receptor triggered by [des-Arg(9)]bradykinin and inhibited by [des-Arg(9),Leu(8)]bradykinin, and the B2 receptor stimulated by bradykinin and antagonized by HOE140. Here we report the cloning of a non-mammalian kinin receptor gene amplified from genomic chicken DNA, The protein predicted from the open reading frame shows 31 and 49% sequence identity to the human B1 and B2 receptors, respectively, suggesting that it represents a G protein-coupled receptor of the kinin receptor family, The recombinantly expressed chicken receptor had IC50 values of 4.7 nM for the authentic ligand, ornithokinin ([Thr(6),Leu(8)]bradykinin), 3.8 nM for HOE140, and greater than or equal to 10 mu M for bradykinin, [des-Arg(9)]bradykinin, and [des-Arg(9),Leu(8)]bradykinin. Ornithokinin and HOE140 at nanomolar concentrations stimulated intracellular inositol phosphate accumulation and induced a significant transient rise in intracelluar free Ca2+, whereas bradykinin was ineffective even at 100 nM. Hence the principal B2 receptor antagonist HOE140 is a potent agonist of the chicken kinin receptor, This unique pharmacological profile classifies the ornithokinin receptor as a novel subtype among kinin receptors and will facilitate further molecular studies on ligand binding and receptor activation.