The Apical Na+-Hco3- Cotransporter Slc4a7 (Nbcn1) Does Not Contribute To Bicarbonate Transport By Mouse Salivary Gland Ducts

The HCO3 (-) secretion mechanism in salivary glands is unclear but is thought to rely on the co-ordinated activity of multiple ion transport proteins including members of the Slc4 family of bicarbonate transporters. Slc4a7 was immunolocalized to the apical membrane of mouse submandibular duct cells. In contrast, Slc4a7 was not detected in acinar cells, and correspondingly, Slc4a7 disruption did not affect fluid secretion in response to cholinergic or -adrenergic stimulation in the submandibular gland (SMG). Much of the Na (+)-dependent intracellular pH (pH (i)) regulation in SMG duct cells was insensitive to 4,4-diisothiocyano-2,2-stilbenedisulfonic acid, S0859, and to the removal of extracellular HCO (3) (-). Consistent with these latter observations, the Slc4a7 null mutation had no impact on HCO (3) (-) secretion nor on pH (i) regulation in duct cells. Taken together, our results revealed that Slc4a7 targets to the apical membrane of mouse SMG duct cells where it contributes little if any to pH (i) regulation or stimulated HCO (3) (-) secretion.