Mediates electroneutral sodium- and carbonate-dependent chloride-HCO3(-) exchange with a Na(+):HCO3(-) stoichiometry of 2:1. Plays a major role in pH regulation in neurons. May be involved in cell pH regulation by transporting HCO3(-) from blood to cell. Enhanced expression in severe acid stress could be important for cell survival by mediating the influx of HCO3(-) into the cells. Also mediates lithium-dependent HCO3(-) cotransport. May be regulated by osmolarity. Activity is inhibited by 4,4'-Di-isothiocyanatostilbene-2,2'-disulfonic acid (DIDS - an inhibitor of several anion channels and transporters). Highly expressed in brain with lower levels in lung, kidney and heart. In the kidney, there is high expression in the inner medulla, localized to the inner medullary collecting duct. In the brain, there seems to be three transcripts each having a different expression pattern. The smaller 3kb transcript has highest expression levels in the thalamus and the largest 9.5kb transcript has highest levels in the substantia nigra. The middle transcript of 4.4kb, which is also the main transcript in kidney, is highly expressed in thalamus. Hence, the highest levels are observed in the thalamus, amygdala and caudate nucleus and very low expression was seen in the corpus callosum. Belongs to the anion exchanger (TC 2.A.31) family.