Molecular Cloning and Functional Expression of a Sodium Bicarbonate Cotransporter from Guinea-Pig Parotid Glands

Abstract

We recently found that the concentration of in guinea-pig saliva is very similar to that of human saliva; however, the entity that regulates transport has not yet been fully characterized. In order to investigate the mechanism of transport, we identified, cloned, and characterized a sodium bicarbonate cotransporter found in guinea-pig parotid glands (gpNBC1). The gpNBC1 gene encodes a 1079-amino acid protein that has 95% and 96% homology with human and mouse parotid NBC1, respectively. Oocytes expressing gpNBC1 were exposed to or Na+-free solutions, which resulted in a marked change in membrane potentials (Vm), suggesting that gpNBC1 is electrogenic. Likewise, a gpNBC1-mediated pH recovery was observed in gpNBC1 transfected human hepatoma cells; however, in the presence of 4, 4-diisothiocyanostilbene-2,2-disulfonic acid, a specific NBC1 inhibitor, such changes in Vm and pHi were not observed. Together, the data show that the cloned guinea-pig gene is a functional, as well as sequence homologue of human NBC1.