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Carbonic anhydrase II binds to and increases the activity of the epithelial sodium-proton exchanger, NHE3

Authors :
R. Todd Alexander
Devishree Krishnan
Lei Liu
Joseph R. Casey
Emmanuelle Cordat
Shane Wiebe
Source :
American Journal of Physiology-Renal Physiology. 309:F383-F392
Publication Year :
2015
Publisher :
American Physiological Society, 2015.

Abstract

Two-thirds of sodium filtered by the renal glomerulus is reabsorbed from the proximal tubule via a sodium/proton exchanger isoform 3 (NHE3)-dependent mechanism. Since sodium and bicarbonate reabsorption are coupled, we postulated that the molecules involved in their reabsorption [NHE3 and carbonic anhydrase II (CAII)] might physically and functionally interact. Consistent with this, CAII and NHE3 were closely associated in a renal proximal tubular cell culture model as revealed by a proximity ligation assay. Direct physical interaction was confirmed in solid-phase binding assays with immobilized CAII and C-terminal NHE3 glutathione- S-transferase fusion constructs. To assess the effect of CAII on NHE3 function, we expressed NHE3 in a proximal tubule cell line and measured NHE3 activity as the rate of intracellular pH recovery, following an acid load. NHE3-expressing cells had a significantly greater rate of intracellular pH recovery than controls. Inhibition of endogenous CAII activity with acetazolamide significantly decreased NHE3 activity, indicating that CAII activates NHE3. To ascertain whether CAII binding per se activates NHE3, we expressed NHE3 with wild-type CAII, a catalytically inactive CAII mutant (CAII-V143Y), or a mutant unable to bind other transporters (CAII-HEX). NHE3 activity increased upon wild-type CAII coexpression, but not in the presence of the CAII V143Y or HEX mutant. Together these studies support an association between CAII and NHE3 that alters the transporter's activity.

Details

ISSN :
15221466 and 1931857X
Volume :
309
Database :
OpenAIRE
Journal :
American Journal of Physiology-Renal Physiology
Accession number :
edsair.doi.dedup.....229cad55e0bf416b9a96155f0cb8aed2
Full Text :
https://doi.org/10.1152/ajprenal.00464.2014