Renal Na/H exchanger NHE-3 and Na-PO4 cotransporter NaP(i)-2 protein expression in glucocorticoid excess and deficient states

Abstract

Administration of pharmacologic doses of glucocorticoid in vivo increases renal proximal tubule apical membrane Na/H exchange and decreases Na/PO4 cotransport activity (1). Current data suggest that the NHE-3 and NaP(i)-2 proteins mediate significant fractions of proximal tubule apical membrane Na/H exchange and Na/PO4 cotransport, respectively. This study examines whether glucocorticoid excess or deficiency affects NHE-3 and NaP(i)-2 protein abundance and the intrarenal distribution of these transporters. Protein abundance of NHE-3 and NaP(i)-2 in control rats was compared to rats rendered glucocorticoid-deficient by bilateral adrenalectomy, and to rats receiving pharmacologic doses of dexamethasone using immunoblots and immunohistochemistry. Adrenalectomy had modest effects on NHE-3 protein abundance, but dexamethasone administration to either adrenalectomized or sham-operated rats significant]y increased NHE-3 protein abundance in both the proximal tubule and thick ascending limb, but not the thin descending limb. Adrenalectomy increased NaP(i)-2 protein abundance in the proximal tubule, whereas dexamethasone administration dramatically suppressed NaP(i)-2 protein on the apical membrane in both adrenalectomized and sham-operated animals. No significant reciprocal increase in subapical NaP(i)-2 staining was seen in the dexamethasone-treated rats. The present study shows that glucocorticoids regulate proximal tubule apical membrane Na/H exchange and NaP(i) cotransport by changes in protein abundance of NHE- 3 and NaP(i)-2, respectively.