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The cloning of a cDNA encoding a G protein-coupled receptor homologous to the endothelin type B receptor, but unable to bind endothelin, was recently reported and termed ETBR-LP. We report here the isolation of a human cDNA encoding a receptor that is highly related to ETBR-LP and which was therefore termed ETBR-LP-2. Comparison of the two amino acid sequences revealed 68% overall homology and 48% identity. As is the case for ETBR-LP, the new receptor is strongly expressed in the human central nervous system (e.g. in cerebellar Bergmann glia, cerebral cortex, internal capsule fibers). Membranes of HEK-293 cells stably expressing ETBR-LP-2 did not bind endothelin-1, endothelin-2, endothelin-3, bombesin, cholecystokinin-8 or gastrin-releasing peptide.

A three-dimensional model for the transmembrane domains of human endothelin-A receptor was built using structural information from bacteriorhodopsin and sequence alignment to other guanine-nucleotide-binding regulatory(G) protein-coupled receptors. Based on this model, 18 amino acids located at the inside of the receptor were mutated and analyzed for binding of the natural ligand endothelin-1 and bosentan, a recently described potent orally active endothelin antagonist [Clozel, M., Breu, V., Gray, G., Kalina, B., Loffler, B.-M., Burri, K., Cassal, J.-M., Hirth, G., Muller, M., Neidhart, W. & Ramuz, H. (1994) Pharmacological characterization of bosentan, a new potent orally active nonpeptide endothelin receptor antagonist, J. Pharmacol. Exp. Ther. 270, 228-235]. Mutation of Gly97, Lys140, Lys159, Gln165 and Phe315, located in transmembrane region 1, 2, 3, 3, and 6, respectively, caused reduced specific binding of 125I-labelled endothelin-1, despite an expression level similar to wild-type endothelin-A receptor. Mutation of Tyr263, Arg326 and Asp351 preserved endothelin-1 binding but caused reduced binding of bosentan. These amino acids, located on transmembrane regions 5, 6 and 7, respectively, are conserved among endothelin-A and endothelin-B receptors but not in other G-protein-coupled receptors. These observations demonstrate a dissociation of the binding site for the peptidic natural agonist endothelin-1 and the synthetic non-peptide antagonist bosentan. They provide the molecular basis for bosentan being a specific antagonist for both, endothelin-A as well as endothelin-B receptors and may in combination with studies on structure/activity relationship support the design of novel and more potent endothelin receptor antagonists.

SPECIFIC AIMSAspirin inhibits IKKβ in vitro; however, the in vivo relevance of the phenomenon is unclear. We have developed a model of severe angiotensin (Ang) II-induced vascular injury and now tested the hypothesis that chronic aspirin treatment of transgenic rats overexpressing the human renin and angiotensinogen genes (dTGR) protects from Ang II-induced end organ damage by inhibiting NF-κB activation in vivo.PRINCIPAL FINDINGSHigh-dose aspirin reduces mortality and renal damage independent of blood pressureRenal glomerulus of untreated 7-wk-old dTGR shows mesangial expansion and podocyte damage. Renal dTGR arterioles exhibit severe changes in wall structure, including proliferation of smooth muscle cells and deposition of dense vacuoles. In contrast, nontransgenic Sprague-Dawley (SD) rats showed no vascular or glomerular damage. Untreated dTGR show signs of glomerular sclerosis and vascular damage with mortality > 50% at wk 7. High-dose aspirin reduced mortality to < 10% whereas low-dose aspirin produ...

The goal of our study was to evaluate and compare the effects of receptor blockade with different endothelin (ET) receptor antagonists on plasma concentrations of ET-1, big ET-1 and ET-3 in conscious rats. Ro 46-2005 (10 mgkg, i.v.), a novel non-peptide antagonist of both ETA and ETB receptors, increased the concentrations of ET-1 in plasma to 200 ± 13% of basal levels (P < 0.001). This effect was dose- and time-dependent and reached a maximum at 15 min. Ro 46-2005 had no effect on plasma concentrations of big ET-1 and only a minor effect on those of ET-3. In contrast to Ro 46-2005, the selective peptide ETA antagonists BQ-123 and FR-139317 had no effect on plasma ET-1 concentrations. The increase in plasma ET-1 concentrations by Ro 46-2005 was most likely not due to de novo synthesis, since big ET-1 levels were not increased and peak levels were reached early after compound injection, but perhaps to displacement of ET-1 from the ETB receptors.