Glucocorticoids stimulate Na+/H+ antiporter in OKP cells.
Previous studies have demonstrated that systemic administration of glucocorticoids stimulates proximal tubule acidification in part by increasing Na+/H+ antiporter activity; however, these studies could not exclude the possibility that changes in Na+/H+ antiporter activity were secondary to glucocorticoid-induced hemodynamic changes. The present study examined the effect of dexamethasone on Na+/H+ antiporter activity in quiescent OKP cells. Na+/H+ antiporter activity was assayed as the initial rate of Na(+)-dependent pH recovery from an acid load. Intracellular pH was measured using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Dexamethasone produced a dose- and time-dependent stimulation of Na+/H+ antiporter activity in OKP cells. Dexamethasone produced a 24% stimulation in Na+/H+ antiporter activity at 10(-9) M and an approximately 40% stimulation of Na+/H+ antiporter activity at both 10(-8) and 10(-6) M. The effect of 10(-6) M dexamethasone was seen within 4 h of incubation and was due to an increase in maximal velocity (Vmax, 3.03 vs. 1.79 pH units/min) with no change in the affinity constant for sodium (KNa, 47.2 vs. 42.0 mM). The stimulatory effect of dexamethasone on Na+/H+ antiporter activity was blocked by cycloheximide and was not observed with 10(-8) M aldosterone. These data demonstrate a direct effect of glucocorticoids to stimulate Na+/H+ antiporter activity in OKP cells.
Baum
M
M
Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235-9063.
Cano
A
A
Alpern
R J
RJ
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004351:Drug Resistance; D005938:Glucocorticoids / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D005938:Glucocorticoids; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D003907:Dexamethasone; D003513:Cycloheximide; C039614:ethylisopropylamiloride