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. Activated by cAMP, protein kinase A and protein kinase C. Inhibited by amiloride and 5-amino-substituted derivatives and activated in a cooperative fashion by intracellular H(+). Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.