Proton-sensing receptor involved in pH homeostasis. May represents an osteoblastic pH sensor regulating cell-mediated responses to acidosis in bone. Mediates its action by association with G proteins that stimulates inositol phosphate (IP) production or Ca(2+) mobilization. The receptor is almost silent at pH 7.8 but fully activated at pH 6.8 (By similarity). Also functions as a metastasis suppressor gene in prostate cancer (By similarity). Belongs to the G-protein coupled receptor 1 family.