Unilateral Ureteral Obstruction Alters Expression of Acid-Base Transporters in Rat Kidney

Purpose: Unilateral ureteral obstruction is a common clinical problem that is often associated with a urinary acidification defect caused by decreased net H+ secretion and/or HCO3- reabsorption. To clarify the molecular mechanisms of these defects we examined expression levels of key acid-base transporters along the renal nephron segments and collecting duct. Materials and Methods: Wistar rats (Mollegard Breeding Centre, Eiby, Denmark) underwent 24-hour unilateral ureteral obstruction, unilateral ureteral obstruction release followed for 4 days or unilateral ureteral obstruction release followed for 4 days plus experimental acidosis induced by NH4Cl oral administration. After sacrifice kidneys were processed for immunoblotting and immunohistochemistry. Results: Semiquantitative immunoblotting revealed that unilateral ureteral obstruction caused significant mean +/- SE down-regulation of type 3 Na+/H+ exchanger to 53% +/- 9%, electrogenic Na+/HCO3- cotransporter to 60% +/- 9%, type 1 bumetanide sensitive Na+-K+(NH4+) -2Cl(-) cotransporter to 64% +/- 7%, electroneutral Na+/HCO3- cotransporter to 43% +/- 4% and anion exchanger (pendrin) to 53% +/- 10% in the obstructed kidney, which was confirmed by immunohistochemistry. After release of unilateral ureteral obstruction down-regulation of these transporters persisted together with marked down-regulation of H+-adenosine triphosphatase in the obstructed kidney. In rats with unilateral ureteral obstruction release followed for 4 days with experimental acidosis induced by NH4Cl oral administration plasma pH and HCO3- were dramatically decreased in response to NH4Cl for 2 days compared with those in sham operated rats with acid loading, indicating a defect in H+ excretion and HCO3- reabsorption after obstruction release. Expression of these transporters did not change in the contralateral nonobstructed kidney of rats with unilateral ureteral obstruction and unilateral ureteral obstruction release followed for 4 days. Conclusions: The expression of renal acid-base transporters is markedly decreased in the obstructed kidney, which may be responsible for the contribution of impaired renal H+ excretion and HCO3- reabsorption to the urinary acidification defect in response to unilateral ureteral obstruction.