Differential expression of electrogenic NBC1 (SLC4A4) variants in rat kidney and pancreas

The purpose of this study was to determine expression and localization of NH2-terminal variants of the electrogenic Na+-HCO3- co-transporter NBC1 (SLC4A4) in the rat kidney and pancreas. We generated two anti-peptide antibodies: alpha333 against the mste start (kidney; kNBC1) and alpha332 against the mede start (pancreas; pNBC1). Transcripts for both NBC1 variants were detected in kidney and pancreas by RT-PCR, though kNBC1 was more prominent in the kidney and pNBC1 was more prominent in the pancreas. Similar protein expression levels were detected by immunoblotting of plasma membranes (PM) from kidney cortex and pancreas. Immunohistochemistry with alpha333 recognized the mste-epitope in the basolateral plasma membrane (BLM) of renal proximal tubule. The mede-protein (alpha332) was similarly localized although staining was much less and more diffuse. In the pancreas, alpha332 stained BLM of acinar and duct cells. Some isolated duct cells were also stained at the apical PM. The mste-protein (alpha333) was absent in acinar cells but was located at the apical PM of duct cells. The data indicate that the two NH2-terminal NBC1 variants are co-expressed in kidney and pancreas, where they may contribute to HCO3- transport and pH regulation. (C) 2003 Elsevier Inc. All rights reserved.