Regulation of renal Na-HCO3 cotransporter: III. Presence and modulation by glucocorticoids in primary cultures of the proximal tubule.
We looked for the presence of the Na-HCO3 cotransporter in primary cultures of the proximal tubule and examined the modulation of this cotransporter by glucocorticoid hormones. Primary cultures of the proximal tubule of the rabbit have Cl-independent, HCO3-dependent 22Na uptake which is DIDS-sensitive. In addition, in cells loaded with BCECF and perfused with Cl-free solution, removal of Na was associated with a decrease in intracellular pH which returned to normal with re-addition of Na. The pH recovery was not inhibited by EIPA but was sensitive to DIDS. These findings are compatible with existence of Na-HCO3 cotransporter in these cells. We examined the role of glucocorticoids on the activity of the Na-HCO3 cotransporter by culturing proximal tubule cells in the presence of hydrocortisone and when confluence was reached, hydrocortisone was deleted from the medium. In the absence of hydrocortisone, the activity of the cotransporter, measured either isotopically or fluorometrically, was significantly decreased, whereas re-addition of hydrocortisone 10(-8) M, restored the activity of the cotransporter to normal levels. The effect of hydrocortisone could not be duplicated by aldosterone, suggesting a glucocorticoid-dependent effect. Dexamethasone, a glucocorticoid without mineralocorticoid activity, stimulated the activity of the cotransporter within physiologic concentrations and this effect was blocked by progesterone. The effect of dexamethasone was time-dependent and was prevented by cycloheximide, a protein synthesis inhibitor. These results demonstrate that primary cultures of the proximal tubule have Na-HCO3 cotransporter activity which is modulated by physiological concentrations of glucocorticoids through a protein synthesis-dependent mechanism.
Ruiz
O S
OS
Section of Nephrology, University of Illinois, Chicago, USA.
Wang
L J
LJ
Pahlavan
P
P
Arruda
J A
JA
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology*; D006854:Hydrocortisone / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism*; D007684:Kidney Tubules / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D027982:Sodium-Bicarbonate Symporters
D002352:Carrier Proteins; D005938:Glucocorticoids; D027982:Sodium-Bicarbonate Symporters; D000584:Amiloride; D003907:Dexamethasone; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C039614:ethylisopropylamiloride; D006854:Hydrocortisone