Expression of sodium bicarbonate cotransporter and its role in pHi regulation in guinea pig salivary glands

Patterns of salivary HCO3 secretion vary and depend on species and gland type. However, the identities of the transporters involved in HCO3 transport and the underlying mechanism of intracellular pH (pHi) regulation in the salivary glands still remain unclear. In this experiment, we examined the expression of the Na/HCO3 cotransporter(NBC) and its role in pHi regulation in guinea pig salivary glands, which can serve as an experimental model to study HCO3 transport in human salivary glands. RT-PCR, immunohistochemistry, and pHi measurements from the 2',7'-bis-(2carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester(BCECF/AM) loaded cells were performed. Amiloride-sensitive Na/H exchange (NHE) played a putative role in pHi regulation in salivary acinar cells, and also appears to be involved in regulation in salivary ducts. In addition to NHE, NBC also played a role in pHi regulation in both acini and ducts. In the parotid gland, NBC1 was functionally expressed in the basolateral membrane (BLM) of acinar cells and the luminal membrane(LM) of ducts. In the submandibular gland, NBC1 was expressed only in the BLM of ducts. The NBC1 expressed in these two types of salivary glands take up HCO3 and are involved in pHi regulation. Although NBC3 immunoreactivity was also detected in submandibular gland acinar cells and in the ducts of both glands, it is unlikely that NBC3 plays any role in pHi regulation. We conclude that NBC1 is functionally expressed and plays a role in pHi regulation in guinea pig salivary glands, but that its localization and role are different depending on the type of salivary glands.