A cDNA encoding a functional bradykinin receptor was isolated from a rat uterus library by a clonal selection strategy using Xenopus laevis oocytes to assay for expression of bradykinin responses. The predicted protein is homologous to the seven transmembrane G protein-coupled superfamily of receptors. Bradykinin and its analogs stimulate a Cl current in oocytes expressing the receptor with the rank order of potency: bradykinin Lys-bradykinin > [Tyr8]-bradykinin >> [Phe6Jbradykinin. This is the rank order of potency observed for these compounds in competitive binding assays on soluble receptor from rat uterus. Des-Arg9-bradykinin (10 pAM) elicits no response when applied to oocytes expressing the receptor; thus, the cDNA encodes a B2 type bradykinin receptor. [This8,DPhe7Jbradykinin, where Thi is I3-(2-thienyl)-alanine, is a very weak partial agonist and inhibits the bradykinin-mediated ion flux, suggesting the cDNA encodes a smooth muscle, rather than a neuronal, B2 receptor subtype. Receptor message has a distribution consistent with previous reports of bradykinin function and/or binding in several tissues and is found in rat uterus, vas deferens, kidney, lung, heart, ileum, testis, and brain. Receptor subtypes are a possibility because several tissues contain two or three message species (4.0, 5.7, and 6.5 kilobases). Southern blot highstringency analysis demonstrated that the rat, guinea pig, and human genomes contain a single gene. As bradykinin is a key mediator of pain, knowledge of the primary structure of this receptor will allow a molecular understanding of the receptor and aid the design of antagonists for pain relief.The nonapeptide bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-ProPhe-Arg) is a mediator of pain, inflammation, vascular permeability, smooth muscle tone in vascular and other tissues, and gastrointestinal function (1-5). Bradykinin can serve as a growth factor (2, 6, 7). Bradykinin binds to G proteincoupled receptors that activate phospholipase C or phospholipase A2 and increases synthesis of inositol trisphosphate or arachadonic acid (8-10).Bradykinin receptors have been classified as two major subtypes, B1 and B2 (1). The bradykinin metabolite des-Arg9-bradykinin is a B1 receptor agonist with potency greater than bradykinin, whereas it is inactive at B2 receptors. B2 receptors have been subdivided into two subtypes, a "neuronal" form, which is fully activated by [Thi58,DPhe7]bradykinin, where Thi is 83-(2-thienyl)-alanine, and a "smooth muscle" form, which is weakly activated by [This'8,DPhe7]bradykinin (11,12). Other subtypes of the B2 receptor have also been suggested (13,14).
