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 gall bladder. In this study, we measured gallbladder Na+/H+ exchange and charact erized the NHE isoforms ex pressed in prairie dogs. Na+/H+ exchange activit y was assessed by measuring amiloride-inhibitable transepithelial Na+ flux and apical Na-22(+) uptake using dimethylamiloride (DMA). HOE-694 was used to determine NHE2 and NHE3 contributions. Basal J(ms)(Na) was higher than J (sm)(Na) with J(net)(Na) absorption. Mucosal DMA inhibited transepithelial Na+ flux in a dose-dependent fashion. causing J(ms)(Na) equal to J(sm)(Na) and blocking J(net)(Na) absorption at 100 muM. Basal Na-22(+) uptake rate w as 10.9 +/- 1.0 mu mol.cm(-2).hr(-1) which was inhibited by similar to 43% by mucosal DMA and similar to 30% by mucosal HOE-694 at 100 muM. RT-PCR and Northern blot analysis demonstrated expression of mRNAs encoding NHE1, NHE 2 and NHE3 in the gallbladder. Expression of NHE1, NHE2 and NHE3 polypeptid es was confirmed using isoform-specific anti-NHE antibodies. These data sug gest that Na+/H+ exchange accounts for a substantial fraction of gallbladde r 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+ up take and transepithelial Na+ absorption.