The pharmacology of cloned B2 bradykinin receptors heterologously expressed in cell lines lacking any endogenous bradykinin receptors was analyzed. The possibility of B2 bradykinin receptor heterogeneity had been proposed on the basis of numerous studies in various tissue preparations. The results reported here permit a direct evaluation of some of these hypotheses by examining the pharmacological properties of cloned bradykinin receptors. A cloned human B2 bradykinin receptor was stably transfected into Chinese hamster ovary cells. The data suggest that in response to bradykinin (BK), the cloned receptor activates both phosphatidylinositol hydrolysis and arachidonic acid release by independent pathways. Thus, the activation of these two second messenger pathways does not require the existence of two B2 bradykinin receptor subtypes. A mouse gene encoding the B2 bradykinin receptor was isolated, and the coding region was expressed in COS-7 cells. This murine receptor exhibited the pharmacological properties of a "classical" B2 bradykinin receptor. A comparison of the pharmacological profiles of cloned human and murine homologs of the B2 bradykinin receptor indicates that both receptors bind agonists with similar properties. However, the two receptors differ dramatically in their affinity for some peptide antagonists. The mouse receptor has a 60- to 80-fold higher affinity for [D-Arg0Hyp3, Thi5,8,D-Phe7]BK and [D-Arg0,Hyp3,D-Phe7]BK than its human homolog. Thus, the species of a bradykinin receptor can have a significant effect on its pharmacology. The cloning, expression, and pharmacological comparison of human and mouse B2 bradykinin receptor genes indicate that some of the previous reports of B2 receptor subtypes can be explained by species differences in a single B2 bradykinin receptor gene.