ATP-induced cytoplasmic calcium mobilization in Bergmann glial cells

ATP receptor mediated Ca2+ signaling was recorded from Bergmann glial cells in cerebellar slices obtained from mice of different ages (postnatal days 6 to 45). To measure the cytoplasmic concentration of Ca2+ ([Ca2+]in), either individual cells were loaded with the Ca(2+)-sensitive probes using the whole cell patch clamp technique or slices were incubated with the dye and the microfluorimetric system was focused on individual cells. Signals were recorded either with single-detector microfluorimetry of the dye fura-2 or by confocal laser scanning microfluorimetry (fluo-3-based recordings). Extracellular application of 100 microns ATP caused a transient elevation of [Ca2+]in, which amplitude was significantly higher in Bergmann glial cell processes as compared with their soma. The rank order of potency for the purinoreceptor agonists was: ADP > or = ATP > UTP >> AMP = adenosine = alpha, beta-methylene-ATP. ATP-triggered Ca2+ transients were reversibly inhibited by the P2 purinoreceptor agonist suramin (100 microM). The involvement of P2 metabotropic receptors is inferred by the observation that ATP mediated cytoplasmic Ca2+ transients were not associated with a measurable change in membrane conductance. The [Ca2+]in increase was due to release from inositol-1,4,5-trisphosphate (InsP3)-sensitive intracellular stores since responses were still observed in Ca(2+)-free extracellular solutions and were irreversibly blocked by the inhibitor of the sarco(endo)plasmic reticulum Ca2+ ATPase, thapsigargin, and by the competitive inhibitor of the InsP3-gated intracellular Ca2+ channels heparin. Intracellular dialysis altered the refilling process of the InsP3-sensitive stores, suggesting that cytoplasmic factors control ATP mediated Ca2+ signalling.