Abstract

The angiotensin IV receptor (AT₄) receptor is widely distributed in both species and tissues. This broad distribution appears to be reflected in an equally diverse repertoire of physiological actions that are mediated through AT₄receptors. This breadth of location and function of AT₄receptors encourages speculation that multiple AT₄ isoforms might exist. In this study, we compared the structural properties of bovine AT₄ receptors from adrenals, kidney, heart, thymus, bladder, aorta, and hippocampus. These comparisons were made using polyacrylamide gel electrophoresis or HPLC analysis of AT₄receptors that had been covalently radiolabeled with the AT₄-specific photoprobe ¹²⁵I-benzoyl phenylalamine-angiotensin IV. Except for the hippocampal AT₄ receptor, the binding subunit in all tissues had a molecular mass of approximately 165 kDa and associated with additional subunits via disulfide linkages. The hippocampal receptor was significantly smaller (150 kDa) and did not appear to possess other disulfide-linked subunits. The receptor was highly glycosylated in all tissues examined. Peptide mapping following cleavage of¹²⁵I-labeled receptor with endopeptidase C or cyanogen bromide resulted in complex cleavage patterns. Together these mapping studies demonstrated the uniqueness of the hippocampal receptor and further suggested that other AT₄ isoforms may exist and be variably distributed among bovine tissues. In agreement with the peptide mapping studies, differences in the binding pattern of several AngIV analogs were observed among the various tissues.