We investigated the effect of extracellular adenosine triphosphate (ATP) on the production of interleukin (IL)-6. whose molecules are capable of stimulating the development of osteoclasts from their hematopoietic precursors as well as are involved in signal transduction systems in human osteoblastic SaM-1 cells. These human osteoblasts Constitutively expressed P2X4, P2X5, P2X6, P2Y2, P2Y5, and P2Y6 purinergic receptors. ATP increased gene- and protein-expression of IL-6 in SaM-1 cells. The expression of the IL-6 mRNA was maximal at I h, and the increase in IL-6 synthesis in response to ATP (10-100 M) occurred in a concentration-dependent manner. Over the same concentration range of the nucleotide that was effective for IL-6 synthesis, ATP caused an increase in the intracellular Ca2+ concentration ([Ca2+](i)), which increase was inhibited by pretreatment with suramin, a P2Y receptor antagonist, or 2-aminoethoxydiphenyl borate (2-APB), an inositol 1,4,5-trisphosphate receptor blocker, but not by the extracellular Ca2+-chelating agent EGTA. The pretreatment of SaM-1 cells with suramin or 2-APB also inhibited the increase in IL-6 synthesis in response to ATP. These findings suggest that extracellular ATP-induced IL-6 synthesis occurs through P2Y receptors and mobilization of Ca2+ from internal stores in human osteoblastic cells. (C) 2004 Elsevier Inc. All rights reserved.