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

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.

Increases in intracellular sodium activate transcription and gene expression via the salt-inducible kinase 1 network in an atrial myocyte cell line

“…Increases in [Na ϩ ] i were accomplished by using the sodium ionophore monensin, as described previously (8). The concentration used (3-5 M) was validated in renal epithelial cells using live cell imaging, and it increased [Na ϩ ] i by ϳ6 -10 mM under steady-state conditions (8). These changes in [Na ϩ ] i do not affect the cell architecture or other vital functions of the cell (8,43).…”

“…This cell line expresses both BNP and ␣-MHC (6, 50). Increases in [Na ϩ ] i were accomplished by using the sodium ionophore monensin, as described previously (8). The concentration used (3-5 M) was validated in renal epithelial cells using live cell imaging, and it increased [Na ϩ ] i by ϳ6 -10 mM under steady-state conditions (8).…”

Analysis of Na+,K+-ATPase Motion and Incorporation into the Plasma Membrane in Response to G Protein–coupled Receptor Signals in Living Cells

“…However, phosphorylation may not affect the intrinsic properties of the Na ϩ ,K ϩ -ATPase (i.e., catalytic activity) but their subcellular distribution. For example, in renal epithelial cells inhibition of Na ϩ ,K ϩ -ATPase activity by catecholamines or phorbol esters is mediated by phosphorylation of the catalytic ␣-subunit, and this event does not affect the catalytic properties of the enzyme while in the plasma membrane but constitutes the triggering signal for its endocytosis into endosomes via a clathrin vesicle-dependent mechanism (Chibalin et al, 1997Yudowski et al, 2000;Efendiev et al, 2002). By contrast, in lung alveolar epithelial cells isoproterenol or DA increase Na ϩ , K ϩ -ATPase activity and this effect is associated with an increased recruitment of active Na ϩ , K ϩ -ATPase molecules to the plasma membrane Lecuona et al, 2000;Ridge et al, 2002).…”

The 14-3-3 Protein Translates the NA+,K+-ATPase α1-Subunit Phosphorylation Signal into Binding and Activation of Phosphoinositide 3-Kinase during Endocytosis

“…In the rodent renal epithelia, phosphorylation of Na ϩ ,K ϩ -ATPase ␣ 1 -subunits (at that are present at the plasma membrane is necessary for dopamine (DA) 1 -induced endocytosis (6 -8) and (at Ser-11) for parathyroid hormoneinduced endocytosis (9). In contrast, recruitment of new molecules to the plasma membrane in response to angiotensin II (10) or serotonin (11) requires the phosphorylation of Na ϩ ,K ϩ -ATPase molecules (Ser-11/Ser-18) present within endosomes. DA-mediated phosphorylation of the ␣ 1 -subunit and Na ϩ ,K ϩ -ATPase endocytosis requires activation of the PKC-isoform, whereas serotonin-and angiotensin II-dependent increase in Na ϩ ,K ϩ -ATPase activity requires activation of the PKC-␤ isoform (11,12).…”