Characterization of Na+/H+ Exchanger Isoform (NHE1, NHE2 and NHE3) Expression in Prairie Dog Gallbladder

Gallbladder Na+ absorption is linked to gallstone formation in prairie dogs. Na+/H+ exchange (NHE) is one of the major Na+ absorptive pathways in gallbladder. In this study, we measured gallbladder Na+/H+ exchange and characterized the NHE isoforms expressed in prairie dogs. Na+/H+ exchange activity was assessed by measuring amiloride-inhibitable transepithelial Na+ flux and apical 22Na+ uptake using dimethylamiloride (DMA). HOE-694 was used to determine NHE2 and NHE3 contributions. Basal JNams was higher than JNasm with JNanet absorption. Mucosal DMA inhibited transepithelial Na+ flux in a dose-dependent fashion, causing JNams equal to JNasm and blocking JNanet absorption at 100 μm. Basal 22Na+ uptake rate was 10.9 ± 1.0 μmol · cm−2· hr−1 which was inhibited by ∼43% by mucosal DMA and ∼30% by mucosal HOE-694 at 100 μm. RT-PCR and Northern blot analysis demonstrated expression of mRNAs encoding NHE1, NHE2 and NHE3 in the gallbladder. Expression of NHE1, NHE2 and NHE3 polypeptides was confirmed using isoform-specific anti-NHE antibodies. These data suggest that Na+/H+ exchange accounts for a substantial fraction of gallbladder apical Na+ entry and most of net Na+ absorption in prairie dogs. The NHE2 and NHE3 isoforms, but not NHE1, are involved in gallbladder apical Na+ uptake and transepithelial Na+ absorption.