Down-regulation of organic anion transporter 2 mRNA expression by nitric oxide in primary cultured rat hepatocytes.

Role of nitric oxide (NO) on the expression of organic anion transporter 2 (OAT2) located in sinusoidal domain of hepatocytes has been investigated. Effect of NO generated in vivo in rat and delivered in vitro to hepatocytes was determined. Lipopolysaccharide (LPS) and spermine NONOate (SPER/NO) were selected as the NO donors for in vivo and in vitro experiments, respectively. Constitutive basal expression of rOAT2 mRNA was detected in the normal rat liver and the level of its expression was decreased by intraperitoneal administration of LPS. This LPS-induced decrement did not occur when aminoguanidine (AG), an inhibitor of iNOS, was co-administered with LPS. The expression of rOAT2 mRNA was detected in hepatocytes, but not in the nonparenchymal cells. In the primary cultured hepatocytes obtained from normal rats (normal hepatocytes), a time-dependent decline of rOAT2 mRNA expression was observed, but not in the hepatocytes obtained from rats pretreated with gadolinium chloride (GdCl3, Gd-hepatocytes), an inhibitor of Kupffer cell activation. The decline of rOAT2 mRNA expression observed in the normal hepatocytes was enhanced by LPS treatment, but not in the Gd-hepatocytes. The LPS-dependent enhancement in the decline of rOAT2 mRNA expression did not occur when the normal hepatocytes were treated with AG or actinomycin D. When the Gd-hepatocytes were treated with SPER/NO, an NO donor, the rOAT2 mRNA expression declined markedly. Combined, our results suggest that rOAT2 mRNA expression in hepatocytes is down-regulated by NO at least at the transcriptional step.