Expression and Function of Na+HCO3− Cotransporters in the Gastrointestinal Tract

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Abstract
Abstract: The stomach, duodenum, colon, and pancreas secrete HCO3− ions into the lumen. Although the importance of HCO3− secretion for the maintenance of mucosal integrity, a normal digestion, and the reabsorption of Cl− has been well established, the molecular nature of the apical and basolateral HCO3− transporting proteins has remained largely unknown. Functional studies have suggested that a Na+HCO3− cotransport system, similar but not identical to the well‐characterized Na+HCO3− cotransporter in the basolateral membrane of the kidney proximal tubule, is present in duodenal and colonic enterocytes, pancreatic ducts cells, and gastric cells and involved in HCO3− uptake from the interstitium. This report describes our work towards understanding the molecular nature, cellular origin, and functional relevance of the Na+HCO3− cotransporter(s) in the stomach and intestine and reviews work by others on the function and localization of Na+HCO3− cotransport processes in the gastrointestinal tract.