MECHANISMS OF ATP-INDUCED CA2+ SIGNALING IN OSTEOCLASTS

We investigate the mechanisms underlying the intracellular calcium pulse that occurs in response to extraceullular adenosine triphosphate (ATP) in osteoclasts. We find that pre-loading of GDP-beta-S abolishes the response in Ca2+-free medium, demonstrating an internal release of Ca2+ via a pathway that involves a G protein. GDP-beta-S does not block in normal Ca2+-containing medium, suggesting that ATP also induces a Ca2+ influx across the cell membrane. We confirmed this using the Mn2+ quenching technique, which shows significant opening of Ca2+ channels. We find a smaller response to adenosine diphosphate (ADP) and 2-methylthio-ATP (2-MeSATP), but no response to beta, gamma-methylene-ATP (AMP-PCP), adenosine monophosphate (AMP) or uridine triphosphate (UTP). Prior application of AMP and UTP, but not AMP-PCP, blocks the response to ATP. Our results indicate that the receptor is a P-2 subtype that is not characteristic of any previously reported P-2 receptor or combination of P-2 receptors.