ATP induces an intracellular calcium pulse in osteoclasts

Adenosine triphosphate (ATP; 50 microM) induces a large, fast, transient increase in intracellular calcium ([Ca2+]i) in rabbit osteoclasts, as measured with fluo-3 on a confocal laser scanning system. The [Ca2+]i increase is most intense in the nuclei of these multinuclear cells, indicating that Ca2+ release is occurring just outside the nuclei. ATP produces a much larger effect than adenosine, indicating that these cells have P2 purinergic receptors. Ca(2+)-free bathing medium and the Ca2+ channel blocker Cd2+ both inhibit but do not block the effect, showing that internal Ca2+ release is involved, but that either the steady state Ca2+ influx or a change in influx is important in modulating the effect. Thapsigargin also inhibits the effect. The ATP effect is repeatable with no change in bathing medium, implying that this signalling pathway has a mechanism for adaptation to progressively higher levels of ATP.