Angiotensin II (angII) is the major effector molecule of the renin angiotensin system and a principal determinant of blood pressure and fluid volume. Progress towards an understanding of the molecular properties of receptors for angII (AT receptors) has lagged that achieved for other components of the renin-angiotensin system. Although evidence of AT receptor heterogeneity has accumulated over two decades, progress towards defining an AT receptor family has been hindered by a lack of information on receptor primary structure. On the basis of newly developed nonpeptidic ligands, the existence of two classes of AT receptors, termed AT1 and AT2, has been proposed. However, no known biological response has been associated with AT2 binding sites. Thus, its existence could not have been predicted by earlier studies. Therefore, diversity within the AT1 receptor class most likely accounts for early evidence of AT receptor heterogeneity. A cDNA encoding a rat vascular smooth muscle AT1 receptor has now been isolated. the amino acid sequence encoded by this clone shares seven hydrophobic, putative membrane spanning structures and conserved amino acid motifs with the rhodopsin-like superfamily of G-protein-coupled receptors. Genomic Southern analysis demonstrates several hybridizing bands to a cloned cDNA probe that suggests the possibility of molecular diversity in AT1 receptors. The objective of this proposal is to define rigorously the molecular basis for this diversity by isolating cDNAs and/or genes encoding additional AT1 receptor subtypes. Using a model system whereby each cloned receptor is uniquely transfected and expressed in a cell line, their pharmacological attributes and biochemical signalling mechanisms will be studied in the absence of AT receptor heterogeneity commonly found in other tissue models. Experiments are proposed to localize the tissue and cellular distribution of AT1 receptor subtypes using in situ hybridization and immuno-cytochemical approaches. These studies should improve knowledge of the pharmacology, function and distribution of AT receptors subtypes. They should improve the rational development of selective therapeutic agents for the treatment of cardiovascular disorders, and provide insights into potential pathophysiological roles of AT receptors.
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