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. Plays an important role in signal transduction (By similarity). Ubiquitously expressed. Expressed in both renal cortex and medulla. In the cortex, present in the majority of cortical tubules. In the medulla, most highly expressed in the proximal tubules (S3) of the outer stripe of the outer medulla. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.