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. Also functions as a metastasis suppressor gene in prostate cancer. Expressed in the lung, testis, heart, brain, spleen, thymus, brown fat, small intestine, colon, peripheral blood leukocytes, macrophages, stomach, ovary and white fat but not in the liver, kidney, and skeletal muscle. Expression in the prostate is weak but detectable. Mice have reduced osteoclasts derived from bone marrow cells, a pH-dependent osteoclast survival effect is also detected. However, the overall bone structures of the mice are not affected. In addition melanoma cell tumorigenesis is significantly inhibited. Belongs to the G-protein coupled receptor 1 family.