Slc26a6 (PAT1) deletion downregulates the apical Na+/H+ exchanger in the straight segment of the proximal tubule.
OBJECTIVE
Slc26a6 (PAT1, CFEX) is a major chloride/base exchanger located on the apical membrane of the kidney proximal tubule. The purpose of the present study was to examine the effect of Slc26a6 deletion on the apical Na+/H+ exchanger 3 (NHE3) in the straight segment (S3) of the proximal tubule, which is the major site for the reabsorption of filtered chloride in the kidney.


METHODS
The proximal tubule S3 segment was perfused and the intracellular pH and apical Na+/H+ exchanger activity and expression were measured.


RESULTS
In the proximal tubule straight segments that were microperfused in vitro, baseline intracellular pH, measured by BCPCF-AM, was 7.10 +/- 0.02 in Slc26a6-/- and 7.33 +/- 0.02 in Slc26a6+/+ animals, a significant reduction in Slc26a6 mutant mice (p < 0.00001). The activity of the apical Na+/H+ exchanger was 0.49 +/- 0.02 pH units/min in Slc26a6+/+ and 0.26 +/- 0.03 pH units/min in Slc26a6-/- animals, a significant reduction in Slc26a6-/- mice (p < 0.0001). Formate-induced intracellular alkalinization, which is mediated via NHE3, was significantly blunted in Slc26a6-/- animals, with an alkalinization magnitude of 0.16 pH unit in Slc26a6-/- versus 0.37 in Slc26a6+/+ animals (p < 0.00001, n = 5 separate animals). Angiotensin II stimulation of NHE3 activity was intact in Slc26a6-/- animals. Buffering capacity was comparable in Slc26a6+/+ and Slc26a6-/- mice. Immunoblotting and immunofluorescent labeling demonstrated comparable NHE3 abundance and distribution in kidney proximal tubules of Slc26a6+/+ and Slc26a6-/- mice.


CONCLUSIONS
In conclusion, Slc26a6 deletion downregulates the apical Na+/H+ exchanger activity in the straight segment of the proximal tubule. The absence of a significant renal sodium loss in Slc26a6-null mice, despite NHE3 downregulation in the in vitro perfused tubules, points to possible activation of signaling pathways that can stimulate the apical Na+/H+ exchanger in vivo.
Petrovic
Snezana
S
Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0585, USA.
Barone
Sharon
S
Wang
Zhaohui
Z
McDonough
Alicia A
AA
Amlal
Hassane
H
Soleimani
Manoocher
M
D000818:Animals; D017920:Antiporters / Q000235:genetics* / Q000502:physiology*; D015536:Down-Regulation; D005260:Female; D017353:Gene Deletion; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D010477:Perfusion; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism; D000076988:Sulfate Transporters
D017920:Antiporters; C466900:Slc26a6 protein, mouse; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000076988:Sulfate Transporters