Forms a proton-gated ion channel with pbo-6 that is activated by acidification of the posterior coelomic space, leading to posterior body wall muscle contraction (pBoc) during the defecation cycle (PubMed:18191228). Probably by regulating the defecation motor program, required for fatty acid uptake by intestinal cells (PubMed:25849533). Does not bind neurotransmitters such as acetylcholine, gamma-aminobutyric acid, glycine, serotonin, glutamate or choline (PubMed:18191228). The functional channel is a heterooligomer of pbo-5 and pbo-6. May self-associate to form homooligomers with negligible ion channel activity. Expressed in the posterior body muscles. Also detected in the RIFL, RIFR and RIS head neurons. Loss of posterior body wall muscle contractions (pBoc). Belongs to the ligand-gated ion channel (TC 1.A.9) family. Acetylcholine receptor (TC 1.A.9.1) subfamily.