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

Carbonic anhydrase II binds to and increases the activity of the epithelial sodium proton exchanger, NHE3. Am J Physiol Renal Physiol. 2015 Jun 3;:ajprenal.00464.2014 Authors: Krishnan D, Liu L, Wiebe SA, Casey JR, Cordat E, Alexander RT 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 proximity ligation assay. Direct physical interaction was confirmed in solid-phase binding assays with immobilized CAII and C-terminal NHE3 GST 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 (CAI...
Source: Am J Physiol Renal P... - Category: Urology & Nephrology Authors: Tags: Am J Physiol Renal Physiol Source Type: research