Extracellular hypotonicity increases Na,K-ATPase cell surface expression via enhanced Na+ influx in cultured renal collecting duct cells.
In the renal collecting duct (CD), the Na,K-ATPase, which provides the driving force for Na+ absorption, is under tight multifactorial control. Because CD cells are physiologically exposed to variations of interstitial and tubular fluid osmolarities, the effects of extracellular anisotonicity on Na,K-ATPase cell surface expression were studied. Results show that hypotonic conditions increased, whereas hypertonic conditions had no effect on Na,K-ATPase cell surface expression in confluent mpkCCDcl4 cells. Incubating cells with amphotericin B, which increases [Na+]i, under isotonic or anisotonic conditions, revealed that Na,K-ATPase recruitment to the cell surface was not directly related to variations of cell volume and osmolarity. The effects of amphotericin B and extracellular hypotonicity were not additive, and both were prevented by protein kinase A and proteasome inhibitors, suggesting a common mechanism of action. In line with this hypothesis, extracellular hypotonicity induced a sustained stimulation of the amiloride-sensitive short-circuit current, indicating increased Na+ influx through the apical epithelial Na+ channel. Moreover, inhibiting apical Na+ entry by amiloride, a blocker of epithelial Na+ channel, or incubating cells in Na+ -free medium prevented the cell surface recruitment of Na,K-ATPase in response to extracellular hypotonicity. Altogether, these findings strongly suggest that extracellular hypotonicity stimulates apical Na+ influx leading to increased [Na+]i, protein kinase A activation, and recruitment of Na,K-ATPase units to the cell surface of mpkCCDcl4 cells.
Service de Néphrologie, Fondation pour Recherches Médicales, Geneva, Switzerland.
Manlio
M
Vinciguerra
Serge
S
Arnaudeau
David
D
Mordasini
Martine
M
Rousselot
Marcelle
M
Bens
Alain
A
Vandewalle
Pierre-Yves
PY
Martin
Udo
U
Hasler
Eric
E
Feraille
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D004789:Enzyme Activation; D045604:Extracellular Fluid / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000201:enzymology*; D051379:Mice; D009994:Osmolar Concentration; D011336:Probability; D012680:Sensitivity and Specificity; D015222:Sodium Channels / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D018709:Statistics, Nonparametric
D027682:Cation Transport Proteins; D015222:Sodium Channels; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase; D000254:Sodium-Potassium-Exchanging ATPase