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P2Y2 receptors are expressed by human osteoclasts of giant cell tumour but do not
mediate ATP-induced bone resorption. W.B. Bowler, A .Littlewood-Evans, G. Bilbe, J.A Gallagher and C.J. Dixon Extracellular nucleotides acting through P2 receptors elicit a range of responses in many cell types. Previously, we have cloned the G-protein coupled P2Y2 receptor from a human osteoclastoma cDNA library and demonstrated its expression by RT- PCR and Southern analysis in a number of skeletal tissues, including a purified population of giant cells. In this study we have localised the expression of P2Y2 receptor transcripts to osteoclasts of giant cell tumour of bone by in situ hybridisation. In osteoblasts and other cell types the P2Y2 receptor is coupled to Ins(1,4,5)P3- mediated Ca2+ release from intracellular stores. In this study the P2Y2 receptor agonists ATP and UTP did not increase cytosolic free calcium concentration ([Ca2+]i) in giant cells isolated from osteoclastoma, whilst the G-protein coupled calcium sensing receptor agonist, Ni2+, elevated [Ca2+]i in the same cells. These data indicate that P2Y2 receptor transcripts expressed by giant cells are not presented to the surface of cells as functional receptor, or alternatively, functional receptors are coupled to an effector other than [Ca2+]i. ATPgS (10mM), but not UTP (10mM), significantly stimulated resorption by an enriched giant cell population. These results indicate that ATP-induced effects on resorption, following direct osteoclastic activation, are mediated by a P2 receptor other than the P2Y2 subtype. Nucleotides, released locally in the bone micro-environment in response to acute trauma or transient physical stress, will interact with a complement of P2 receptors expressed by both osteoclasts and osteoblasts to influence the remodelling process. |