Identification of a domain of ETA receptor required for ligand binding

Abstract
Various chimeric ETA and ETB receptors were produced in CHO cells for the elucidation of a specific domain which influences the affinity of the receptor toward BQ‐123, a selective ETA antagonist. Replacement of the first extracellular loop domain (B‐loop) of the ETA receptor with the corresponding domain of the ETB receptor, reduced the inhibition by BQ‐123 drastically, while the replacements of other extracellular domains of ETA did not. By contrast, the introduction of the B‐loop of ETA in place of the corresponding domain of the ETB receptor endowed the ETB‐based chimeric receptor with a sensitivity to BQ‐123. These observations suggest that the B‐loop domain of the ETA receptor is involved in ligand binding.