Modulation of Na+,K+-ATPase activity by a tyrosine phosphorylation process in rat proximal convoluted tubule

1. In the rat kidney proximal convoluted tubule, epidermal growth factor and insulin have been reported to stimulate Na+ reabsorption. Because most of the effects of these growth factors are mediated by a process of tyrosine phosphorylation and Na+,K+-ATPase drives Na+ reabsorption, the influence of tyrosine kinases and tyrosine phosphatases on Na+,K+-ATPase activity located in the proximal convoluted tubule was evaluated. 2. Activation of receptor tyrosine kinases by epidermal growth factor and insulin stimulated ouabain-sensitive Rb-86(+) uptake. The effects of epidermal growth factor and insulin were prevented by genistein, a tyrosine kinase inhibitor, but were unaffected by GF109203X, a protein kinase C inhibitor. 3. Inhibition of tyrosine phosphatases by orthovanadate (10(-7) and 10(-6) M) mimicked the effects of activation of receptor tyrosine kinases: stimulation of the ouabain-sensitive Rb-86(+) uptake and of the hydrolytic activity of Na+,K+-ATPase under rate-limiting Na+ concentration, and absence of modification of the maximal activity (V-max) of the enzyme. The effects of orthovanadate and insulin on the ouabain-sensitive Rb-86(+) uptake were not additive. 4. The present results show that both activation of receptor tyrosine kinases and inhibition of tyrosine phosphatases stimulate the Na+,K+-ATPase activity through a common mechanism. Thus, a tyrosine phosphorylation process directly controls the Na+,K+-ATPase activity and contributes to the physiological control of water and solute reabsorption in the proximal convoluted tubule.