This gene encodes a sodium bicarbonate cotransporter (NBC) involved in the regulation of bicarbonate secretion and absorption and intracellular pH. Mutations in this gene are associated with proximal renal tubular acidosis. Multiple transcript variants encoding different isoforms have been found for this gene. 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.