Involved in pH regulation to eliminate acids generated by active metabolism or to counter adverse environmental conditions. Major proton extruding system driven by the inward sodium ion chemical gradient. Seems to play an important role in colonic sodium absorption. Interacts with CHP1 and CHP2. High levels in intestine and kidney. Phosphorylated (Possible). Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family. The number, localization and denomination of hydrophobic domains in the Na(+)/H(+) exchangers vary among authors.