Immunohistochemical localization of distinct angiotensin II AT1 receptor isoforms in the kidneys of the Sprague-Dawley rat and the desert rodent Meriones crassus

Employing a purified lgG fraction of a polyclonal anti-AT1 receptor anti-body, raised against a synthetic octapeptide encompassing residues 14-21 of the first extracellular domain of the AT1 polypeptide, selective AT1 receptor expression was immunohistochemically demonstrable within renal structures in Sprague-Dawley (SD) rats and the desert rodent Meriones crassus. In both animal models, prominent AT1 receptor labelling was evident in renal vascular elements, particularly cortical inter-lobular arteries (IA) as well as vasa recta bundles in the inner stripe of the outer medulla. Less intense labelling was observed among peritubular capillary endothelia within the deep cortex, and at both the outer stripe and the inter-bundle regions of the inner stripe of the outer medulla. The binding of the anti-peptide anti-body was, however, lacking among glomeruli and, except for the intense labelling confined to basement membranes of Bowman's capsule of deep nephrons, was virtually absent in all renal tubular structures of both animal models. Structural assessment of the expressed AT1 receptors by two-dimensional Western blotting revealed that a spectrum of structurally distinct AT1 receptor isoforms is expressed in the renal tissues of both animal models. This spectrum was constituted by isoforms of equal size (70 kDa) but distinct pls in SD rats, and of both different sizes (67-73 kDa) and isoelectric points in M. crassus. In either species, the charge and/or size heterogeneity of AT1 receptor isoforms may be attributed in part to differential post-translational glycosylation mechanisms of the AT1 receptor polypeptide backbone. The potential for the differential glycosylation state of AT1 receptors to alter recognition properties may add another level of complexity to tissue-specific and/or species-specific mechanisms underlying angiotensin II interactions in the kidney.