Unilateral ureteral obstruction alters expression of acid-base transporters in rat kidney.
OBJECTIVE
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 HCO(3)(-) 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.


METHODS
Wistar rats (Møllegard 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 NH(4)Cl 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(+)/HCO(3)(-) cotransporter to 60% +/- 9%, type 1 bumetanide sensitive Na(+)-K(+)(NH(4)(+)) -2Cl(-) cotransporter to 64% +/- 7%, electroneutral Na(+)/HCO(3)(-) 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 NH(4)Cl oral administration plasma pH and HCO(3)(-) were dramatically decreased in response to NH(4)Cl for 2 days compared with those in sham operated rats with acid loading, indicating a defect in H(+) excretion and HCO(3)(-) 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 HCO(3)(-) reabsorption to the urinary acidification defect in response to unilateral ureteral obstruction.
Water and Salt Research Center, University of Aarhus, Aarhus, Denmark.
Guixian
G
Wang
Troels
T
Ring
Chunling
C
Li
Soo Wan
SW
Kim
Jianguo
J
Wen
Jens Christian
JC
Djurhuus
Søren
S
Nielsen
Jørgen
J
Frøkiaer
D000818:Animals; D007668:Kidney / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000096:biosynthesis; D006180:Proton-Translocating ATPases / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D027982:Sodium-Bicarbonate Symporters / Q000096:biosynthesis; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis; D028021:Sodium-Potassium-Chloride Symporters / Q000096:biosynthesis; D064466:Solute Carrier Family 12, Member 1; D000076988:Sulfate Transporters; D014517:Ureteral Obstruction / Q000378:metabolism*
D026901:Membrane Transport Proteins; C578714:SLC12A1 protein, human; C085609:SLC26A4 protein, human; C498898:SLC4A4 protein, human; C578716:Slc12a1 protein, rat; D027982:Sodium-Bicarbonate Symporters; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D000076988:Sulfate Transporters; D006180:Proton-Translocating ATPases