Acid-induced stimulation of Na-Pi cotransport in OK cells: molecular characterization and effect of dexamethasone.
Alterations in systemic acid/base balance affect renal Pi excretion. In the present study, the effects of an acidic pH on apical Na-dependent Pi (Na-Pi) cotransport were analyzed using OK cells (opossum kidney cell line). Cells were maintained at either pH 7.4 or 7.1 (altered HCO3- concentration at constant PCO2). Incubation in acidic medium led to an increase in Na-Pi cotransport activity, which was characterized by a transient, initial response (2-4 h, 25% increase) followed by a sustained response (24 h, 75% increase). Increased Na-Pi cotransport activity (24 h) was sensitive to inhibition by parathyroid hormone. Actinomycin D did not abolish the acid-induced increases (initial and sustained responses). Cycloheximide abolished the increase in Na-Pi cotransport observed after 24 h. The increase in Na-Pi cotransport (24 h) was prevented by dexamethasone (2 x 10(-6) M). Western blots showed a twofold (3 h) and two- to threefold (24 h) increase in NaPi-4 protein after acid exposure. Cycloheximide prevented the late increase in NaPi-4 protein abundance. Also dexamethasone reduced the increase in specific protein content. In conclusion, the exposure of OK cells to an acidic medium causes a stimulation of the NaPi-4 cotransporter that is prevented by dexamethasone.
Jehle
A W
AW
Institute of Physiology, University of Zurich, Switzerland.
Forgo
J
J
Biber
J
J
Lederer
E
E
Krapf
R
R
Murer
H
H
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001692:Biological Transport; D002245:Carbon Dioxide; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009893:Opossums; D010313:Partial Pressure; D010710:Phosphates / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D019379:Teriparatide / Q000494:pharmacology
D001639:Bicarbonates; D002352:Carrier Proteins; D010710:Phosphates; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D019379:Teriparatide; D002245:Carbon Dioxide; D003609:Dactinomycin; D003907:Dexamethasone; D003513:Cycloheximide