Abstract 248: Non-genomic Vasoconstrictor Effect of Aldosterone via Angiotensin II Type 1 (AT1) Receptor in Mice Mesenteric Arterioles : Role of AT1 Receptor Dimerization
We recently reported that aldosterone shows non-genomic vasoconstrictor effect in rat coronary arterioles and this effect was blocked by AT1 receptor blocker (ARB). Any specific membrane receptor for aldosterone has not been determined, and therefore a precise mechanism for aldosterone’s effect via AT1 receptor remains unclear. Recently it was reported that ATz1 receptor dimerization enhances AT1 receptor responsiveness. We investigated the role of AT1 receptor in aldosterone-mediated, non-genomic vasoconstriction in the mesenteric arterioles and the involvement of AT1 receptor dimerization in it. The mesenteric arterioles (80–160 μm) were isolated from C57BL/6J mice and AT1a knockout mice (age, 15–20 weeks), cannulated, and pressurized at 60 mmHg. The effect of aldosterone (10−15 to 10−6 M) on the mesenteric arteriolar diameter was examined. Then the effects of spironolactone (10−6M), ARB valsartan and candesartan (10−4M), superoxide dismutase (SOD, 300 U/ml), NADPH oxidase inhibitor apocynin (10−4M), and transglutaminase (an enzyme to dimerize AT1 receptor) inhibitors cystamine (5×10−4M) on aldosterone-induced changes in the mesenteric arteriolar diameter were examined. Aldosterone produced endothelium-dependent vasoconstriction in a dose-dependent manner and the maximum diameter change from the baseline was -7.1±2.0% in C57BL/6J mice (n = 15, p < 0.05). This vasoconstrictor effect of aldosterone was blocked by valsartan, candesartan, SOD, apocynin and cystamine, but not by spinoloractone. In AT1 knockout mice, no vasomotor effect of aldosterone was detected. To confirm the dimerization of AT1 receptor, cultured vascular endothelial cells were exposed to 10−6 M aldosterone for 10 minutes. Dimerized AT1 recepor proteins were detected as double molecular mass of monomeric AT1 receptor by Western blot analysis and cystamine suppressed the aldosterone-induced formation of AT1 dimers. Thus, aldosterone caused superoxide-mediated vasoconstriction in the mice mesenteric arterioles, and it was blocked by ARB, genetic AT1a receptor knockout, and AT1 receptor dimerization inhibitor. These suggest that AT1 receptor dimerization by aldosterone is a mechanism for its non-genomic vasoconstrictor effect in the resistance arterioles.