Serves some physiological function other than regulation of cellular pH. Excretory cell. In early stage larva, expressed in the twin excretory cell processes. At later larval stages, expression is more restricted, resulting in a 'beads on a chain' appearance. Phosphorylated. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.