Intracellular sodium modulates the expression of angiotensin II subtype 2 receptor in PC12W cells

Although the angiotensin II subtype 2 receptor (AT(2)-R) is expressed abund antly in the adrenal medulla, its physiological significance has not yet be en determined. To obtain fundamental knowledge of the regulation of AT(2)-R expression in the adrenal medulla, we investigated the effects of modulati ng several ion channels on AT(2)-R expression in PC12W cells. Experiments w ere performed after 24 hours of serum depletion under subconfluent conditio ns. After 48 hours of treatment with various agonists or antagonists, the r eceptor density and mRNA level of AT(2)-Rs were quantified by I-125-[Sar(1) , Ile(8)]angiotensin II binding and Northern blot analysis. Ouabain (10 to 100 nmol/L) and insulin (10 to 100 nmol/L) dose-dependently increased recep tor density and mRNA level. Analysis of the binding characteristics reveale d that the ouabain-dependent increase in AT(2)-R levels was due to an incre ase in binding capacity without a change in the K-d value. These increases were blocked by lowering the Na+ concentration in the medium. A low concent ration of the sodium ionophore monensin (10 nmol/L), the K+-channel blocker quinidine (10 mu mol/L), and the ATP-sensitive K+-channel blockers tolbuta mide (100 mu mol/L) and glybenclamide (10 mu mol/L) also significantly incr eased receptor density, but the ATP-sensitive K+-channel agonist cromakalim (100 mu mol/L) decreased receptor density significantly (P<0.01). Nifedipi ne (10 mu mol/L) decreased basal receptor density and completely blocked th e increase in receptor density caused by these agents. The increase in rece ptor density caused by an increase in intracellular Na+ was accompanied by an increase in mRNA level, whereas the ATP-sensitive K+-channel blockers di d not change mRNA level, Nifedipine slightly decreased mRNA level. These re sults suggest that AT(2)-R expression is sensitively regulated by intracell ular cation levels. The change in intracellular Na+ level transcriptionally regulates AT(2)-R expression whereas the K+-channel blocker-dependent upre gulation appears to be at least in part posttranslational.