Electrogenic sodium bicarbonate cotransporter 1

Electrogenic sodium bicarbonate cotransporter 1 (NBCe1) is a membrane transport protein that in humans is encoded by the 'SLC4A4' gene.
Function.
Sodium bicarbonate cotransporters (NBCs) 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. Sodium bicarbonate cotransport is involved in bicarbonate secretion/absorption and intracellular pH regulation. Romero and Boron (1999) reviewed NBCs. Soleimani and Burnham (2000) reviewed NBCs and their regulation in physiologic and pathophysiologic states.[supplied by OMIM]
Clinical significance.
In brain, NBCe1 is predominantly expressed by astrocytes. NBCe1 may participate in regulation of brain extracellular space pH. Some mutations in NBCe1 have been associated with Familial hemiplegic migraine. Other NBCe1 mutations disrupt kidney bicarbonate transport and cause proximal renal tubular acidosis.
Splice variants.
NBCe1-A aka kNBC1 (mainly expressed in the kidney)
NBCe1-B aka pNBC1 (expressed in the pancreas and elsewhere)
NBCe1-C (expressed in the brain)
Distribution.
The renal SLC4A4 gene product NBCe1-A is specifically expressed in the basolateral membranes of proximal tubule epithelia.