NBC1 - Electrogenic Sodium Bicarbonate Cotransporter 1 - SLC4A4

Family:
Sodium Bicarbonate Cotransporter (NBCs) are members of the anion exchanger (AE) family

Subgrops:
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

Topology:
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.

Function:
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)