Agonist-dependent Regulation of Renal Na+, K+-ATPase Activity Is Modulated by Intracellular Sodium Concentration

Riad Efendiev,Alejandro M Bertorello,Ruben Zandomeni,Angel R Cinelli,Carlos H Pedemonte

doi:10.1074/jbc.m108182200

Abstract

We tested the hypothesis that the level of intracellular sodium modulates the hormonal regulation of the Na(+),K(+)-ATPase activity in proximal tubule cells. By using digital imaging fluorescence microscopy of a sodium-sensitive dye, we determined that the sodium ionophore monensin induced a dose-specific increase of intracellular sodium. A correspondence between the elevation of intracellular sodium and the level of dopamine-induced inhibition of Na(+),K(+)-ATPase activity was determined. At basal intracellular sodium concentration, stimulation of cellular protein kinase C by phorbol 12-myristate 13-acetate (PMA) promoted a significant increase in Na(+),K(+)-ATPase activity; however, this activation was gradually reduced as the concentration of intracellular sodium was increased to become a significant inhibition at concentrations of intracellular sodium higher than 16 mm. Under these conditions, PMA and dopamine share the same signaling pathway to inhibit the Na(+),K(+)-ATPase. The effects of PMA and dopamine on the Na(+),K(+)-ATPase activity and the modulation of these effects by different intracellular sodium concentrations were not modified when extracellular and intracellular calcium were almost eliminated. These results suggest that the level of intracellular sodium modulates whether hormones stimulate, inhibit, or have no effect on the Na(+),K(+)-ATPase activity leading to a tight control of sodium reabsorption.

Highlights

We tested the hypothesis that the level of intracellular sodium modulates the hormonal regulation of the Na؉,K؉-ATPase activity in proximal tubule cells
We demonstrate that direct stimulation of cellular protein kinase C by the phorbol ester phorbol 12-myristate 13-acetate (PMA) leads to either activation or inhibition of Naϩ,Kϩ-ATPase activity depending on the intracellular sodium concentration
The basal Naϩ,Kϩ-ATPase activity and its inhibition by either PMA or dopamine were not affected by changes of extracellular or intracellular calcium. This is the first time that changes in intracellular sodium were measured to correlate accurately changes in this ion concentration with the regulation of the Naϩ,Kϩ-ATPase activity by dopamine and PMA

Summary

Introduction

We tested the hypothesis that the level of intracellular sodium modulates the hormonal regulation of the Na؉,K؉-ATPase activity in proximal tubule cells. The effects of PMA and dopamine on the Na؉,K؉-ATPase activity and the modulation of these effects by different intracellular sodium concentrations were not modified when extracellular and intracellular calcium were almost eliminated These results suggest that the level of intracellular sodium modulates whether hormones stimulate, inhibit, or have no effect on the Na؉,K؉-ATPase activity leading to a tight control of sodium reabsorption. Increases in dietary sodium intake or acute sodium loading lead to natriuresis accompanied by elevated urinary dopamine excretion, which suggested that dopamine produced endogenously by the epithelial proximal tubule cells might contribute to the natriuretic response [2,3,4]. We demonstrate that direct stimulation of cellular protein kinase C by the phorbol ester PMA leads to either activation or inhibition of Naϩ,Kϩ-ATPase activity depending on the intracellular sodium concentration

Methods

Results

Conclusion