Abstract
NaCl absorption in the gastrointestinal tract is mediated by coupled Na+/H+ and Cl−/HCO3− exchangers. Recent studies have suggested that SLC26A3 (also called DRA) is a major Cl−/HCO3− exchanger in the colon, yet little is known about its functional properties. Since multiple isoforms of the Cl−/HCO3− exchanger are co-expressed in an intact colonic cell, complicating the functional analysis of an individual isoform, we generated an N-terminal hemagglutinin (HA) epitope-tagged human SLC26A3 construct and expressed transiently in CHO cells by using inducible gene expression systems. Cl−/HCO3− exchange activity was assessed by measuring intracellular pH using fluorescent dye BCECF. When the cells were induced DRA, the cells were conferred 100μM DIDS insensitive Cl−/HCO3− exchange activity. Pharmacological analyses revealed that SLC26A3 was inhibited by 50 μM niflumic acid (90%), by 50 μM tenidap (30%). Ion selectivity experiments showed that SLC26A3 can also transport Br− and I− but not SO42−. Increased intracellular cAMP and/or Ca2+ elicited by enterotoxins and some neurotransmitters is known to result in inhibition of electroneutral NaCl absorption in intestinal epithelium. In SLC26A3-expressing cells, elevating [Ca2+ ]i with ionomycin rapidly inhibited SLC26A3 activity, while did not affect increasing cAMP. Immunoblotting and fluorescence imaging analysis of cells before and after treatment of ionomycin revealed no visible differences in the density or distribution of SLC26A3. [Jpn J Physiol 55 Suppl:S85 (2005)]
