AT 1Receptor Gene Regulation in Cardiac Myocytes and Fibroblasts

Abstract

The regulation of the AT 1receptor gene was studied in neonatal cardiomyocytes and fibroblasts in vitro. Incubation with angiotensin II (Ang II) resulted in a time-dependent and dose-dependent decrease in AT 1mRNA levels in both cardiomyocytes and fibroblasts. Co-incubation with Ang II and the specific AT 1antagonist losartan prevented the decrease in AT 1mRNA whereas the AT 2antagonist PD123319 was ineffective in preventing the decrease in AT 1mRNA. Because Ang II is known to decrease cAMP levels in cardiomyocytes, the role of cAMP in the regulation of the AT 1gene was examined. Treatment with the adenylyl cyclase stimulant forskolin or the cAMP stereoisomer Sp-cAMPS increased AT 1mRNA levels or prevented the Ang II mediated decrease in AT 1mRNA levels. The role of calcium in the regulation of the AT 1gene was determined by incubation with the calcium ionophores A23187 and ionomycin (0.0625–1 μ m) which resulted in a profound, dose-dependent decrease in AT 1mRNA levels. Treatment with BAPTA, an intracellular chelator of calcium, prevented the Ang II-mediated decrease in AT 1mRNA. Therefore Ang II is a potent negative regulator of the AT 1gene in cardiomyocytes and fibroblasts via the AT 1receptor. This Ang II mediated decrease in AT 1mRNA is mediated by two complementary mechanisms involving cAMP and intracellular calcium.