Sodiumhydrogen antiporter 3, found on the apical side of the epithelial cells of the proximal tubule of the nephron of the kidney, is primarily responsible for maintaining the balance of sodium.
It is found on the apical side of the epithelial cells of the proximal tubule of the nephron of the kidney, in the apical membrane of enterocytes of the intestine, as well as the basolateral side of both duodenal and pancreatic cells responsible for the release of HCO3 into the duodenal lumen. It is primarily responsible for maintaining the balance of sodium. 
