NBC1 - Electrogenic Sodium Bicarbonate Cotransporter 1 - SLC4A4
Sodium Bicarbonate Cotransporter (NBCs) are members of the anion exchanger (AE) family
In humans, the AE family is composed of 10 paralogous members, among which are the proteins that perform Na+-independent Cl-HCO3- exchange (e.g., AEs 1-3), Na+-coupled anion exchange (e.g., NDCBE), and electroneutral (e.g., NBCn1) and electrogenic (e.g., NBCe1 and NBCe2) Na/HCO3 cotransport
All AE proteins are hypothesized to share a similar topology in the cell membrane. They have relatively long cytoplasmic N-terminal domains composed of a few hundred to several hundred residues, followed by 10-14 transmembrane domains, and end with relatively short cytoplasmic C-terminal domains composed of ~30 to ~90 residues.
Sodium bicarbonate cotransporters mediate the coupled movement of sodium and bicarbonate ions across the plasma membrane of many cells. This is an electrogenic process with an apparent stoichiometry of 3 bicarbonate ions per sodium ion. These proteins are important for the regulation of intracellular pH (pHi) and play crucial roles in the epithelial absorption of HCO3- (e.g., in the renal proximal tubule) and secretion of HCO3- (e.g., in the pancreatic duct)