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Modulation of Na+,K(+)-ATPase activity by a tyrosine phosphorylation process in rat proximal convoluted tubule
E Féraille1, M L Carranza, M Rousselot
1Division de Néphrologie, Hôpital Cantonal Universitaire, Genève, Switzerland.
Abstract:
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 86Rb+ 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 86Rb+ uptake and of the hydrolytic activity of Na+,K(+)-ATPase under rate-limiting Na+ concentration, and absence of modification of the maximal activity (Vmax) of the enzyme. The effects of orthovanadate and insulin on the ouabain-sensitive 86Rb+ 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.
Insights
Tyrosine phosphorylation directly controls kidney Na+,K+-ATPase activity. This mechanism, influenced by growth factors like EGF and insulin, regulates sodium reabsorption in the proximal tubule.
Area of Science:
- Nephrology
- Molecular Biology
- Biochemistry
Background:
- Epidermal growth factor (EGF) and insulin stimulate Na+ reabsorption in the rat kidney proximal convoluted tubule.
- These effects are largely mediated by tyrosine phosphorylation.
- Na+,K+-ATPase is the primary driver of Na+ reabsorption in this segment.
Purpose of the Study:
- To investigate the role of tyrosine kinases and phosphatases in regulating Na+,K+-ATPase activity in the rat kidney proximal convoluted tubule.
- To elucidate the signaling pathways involved in growth factor-mediated sodium reabsorption.
Main Methods:
- Assessed ouabain-sensitive 86Rb+ uptake as a measure of Na+,K+-ATPase activity.
- Utilized EGF, insulin, genistein (tyrosine kinase inhibitor), and orthovanadate (tyrosine phosphatase inhibitor).
- Measured hydrolytic activity and Vmax of Na+,K+-ATPase.
Main Results:
- EGF and insulin activated receptor tyrosine kinases, stimulating Na+,K+-ATPase activity, an effect blocked by genistein.
- Inhibition of tyrosine phosphatases with orthovanadate mimicked EGF and insulin effects, stimulating Na+,K+-ATPase activity.
- The effects of orthovanadate and insulin were not additive, suggesting a common pathway.
Conclusions:
- Tyrosine phosphorylation directly regulates Na+,K+-ATPase activity in the proximal convoluted tubule.
- Both receptor tyrosine kinase activation and tyrosine phosphatase inhibition stimulate Na+,K+-ATPase via a common mechanism.
- This pathway plays a crucial role in the physiological control of water and solute reabsorption.