Na+/H+ exchanger which mediates the transient acidification of the coelomic space and plays a role in contraction of posterior body muscles during defecation (PubMed:18191228, PubMed:18291648, PubMed:23319594). Probably by regulating the defecation motor program, required for fatty acid uptake by intestinal cells (PubMed:25849533). Interacts (via C-terminus) with cmd-1. Detected in the posterior cells of the intestine. Loss of posterior body wall muscle contractions (pBoc), weak movement of tail, weak enteric muscle contractions, severe reduction in acidification of the pseudocoelom and slight constipation. Normal oscillatory Ca(2+) signaling in the intestine with unaffected defecation period and timing and normal locomotion. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.