Cellular responses to ATP/UTP and analogs are mediated by G-protein coupled P2Y receptors and have been proposed to play a role in the regulation of bone metabolism. Using a degenerate PCR approach on MG-63 cell cDNA we found PCR fragments coding for human P2Y1 and a new receptor, P2Y6. cDNA cloning of the P2Y6 receptor identified three cDNA isoforms. Two contained the same contiguous ORFs but differed in their 5' UTRs and may therefore originate by alternative splicing whereas the third represents a pseudogene. Analysis of P2Y receptor subtype expression in human bone and the osteoblastic cell lines OHS-4 and MG-63 by RT-PCR showed that all known human P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, and P2Y7) were expressed. In contrast, analysis of brain-derived cell lines suggests that a selective expression of P2Y receptor subtypes occurs in brain tissue.