Role of protein kinase C in beta 2-adrenoceptor function in cultured rat proximal tubule epithelial cells

Abstract

Renal sodium excretion is regulated by the adrenergic system. We recently demonstrated the presence of functional beta 2-adrenoceptors (beta 2-AR) in cultured rat proximal tubule epithelial cells beta 2-AR activation resulted in increases in Na-K-adenosinetriphosphatase (Na-K-ATPase) activity and transcellular sodium transport as a consequence of increased apical sodium entry. The purpose of this study was to determine the role of protein kinase C (PKC) on beta 2-AR-dependent increases in Na-K-ATPase activity and sodium transport in proximal tubules. To determine the effect of PKC on basal function, cultured rat proximal tubule cells were exposed to phorbol 12-myristate 13-acetate (PMA). PMA increased apical Na entry (+/-80%), decreased Na-K-ATPase activity (+/-25%), and prevented increases in Na-K-ATPase activity after sodium entry facilitation with monensin. Decreases in Na-K-ATPase activity were associated with decreases in sodium transport (+/-30%). To determine whether beta 2-AR function was transduced by PKC, PKC activity was measured in cells exposed to the selective beta 2-AR agonist metaproterenol. Metaproterenol caused increases in PKC activity, which were blocked by a beta 2-AR but not by a beta 1-AR-receptor antagonist. beta 2-AR-dependent increases in apical Na entry, Na-K-ATPase activity, and sodium transport were blocked by calphostin C or staurosporine. To determine whether PKC had additional effects on beta 2-AR function, cells were exposed to metaproterenol and PMA. Metaproterenol-induced increases in Na-K-ATPase activity and sodium transport were blocked by PMA. In conclusion, beta 2-AR-mediated increases in Na-K-ATPase activity and sodium flux are transduced by PKC acting through increases in apical Na entry. However, activation of PKC by phorbol esters inhibits beta 2-AR-dependent increases in Na-K-ATPase activity and sodium transport.