DIRECT EVIDENCE FOR MULTIPLE ENDOTHELIN RECEPTORS

Competition binding experiments and peptide mapping techniques were employed in order to directly address the possible existence of endothelin (ET) receptor subtypes in the atria. Competition binding assays for {sup 125}I-labeled Et-1 or {sup 125}I-labeled Et-3 bovine atrial membrane preparations suggest the existence of two ET receptor subtypes, one of which binds ET-1 and ET-3 with a similar affinity while the other shows preference for ET-3. However, cross-linking experiments of both peptides to this tissue resulted in the identification of a single 50-kDa protein. To identify directly the existence of multiple ET receptors, peptide mapping of cross-linked {sup 125}I-labeled ET-1 or {sup 125}I-labeled ET-3 receptors was conducted. Different peptide maps were obtained only under conditions that preferentially label one receptor subtype. These results indicate, for the first time, the existence of two ET receptor subtypes in the atria which differ from each other in both their binding characteristics and primary structure.