ATP-INDUCED CYTOPLASMIC CALCIUM MOBILIZATION IN BERGMANN GLIAL-CELLS

ATP receptor mediated Ca2+ signalling was recorded from Bergmann glial cells in cerebellar slices obtained from mice of different ages (post natal days 6 to 45). To measure the cytoplasmic concentration of Ca2([Ca2+](in)), either individual cells were loaded with the Ca2+-sensit ive probes using the whole cell patch clamp technique or slices were i ncubated with the dye and the microfluorimetric system was focused on individual cells. Signals were recorded either with single-detector mi crofluorimetry of the dye fura-2 or by confocal laser scanning microfl uorimetry (fluo-3-based recordings). Extracellular application of 100 mu M ATP caused a transient elevation of [Ca2+](in), which amplitude w as significantly higher in Bergmann glial cell processes as compared w ith their soma. The rank order of potency for the purinoreceptor agoni sts was: ADP greater than or equal to ATP > UTP >> AMP = adenosine = a lpha,beta-methylene-ATP. ATP-triggered Ca2+ transients were reversibly inhibited by the P-2 purinoreceptor agonist suramin (100 mu M) The in volvement of P-2 metabotropic receptors is inferred by the observation that ATP mediated cytoplasmic Ca2+ transients were not associated wit h a measurable change in membrane conductance. The [Ca2+](in) increase was due to release from inositol-1,4,5-trisphosphate (InsP(3))-sensit ive intracellular stores since responses were still observed in Ca2+-f ree extracellular solutions and were irreversibly blocked by the inhib itor of the sarco(endo)plasmic reticulum Ca2+ ATPase, thapsigargin, an d by the competitive inhibitor of the InsP(3)-gated intracellular Ca2 channels heparin. Intracellular dialysis altered the refilling proces s of the InsP(3)-sensitive stores, suggesting that cytoplasmic factors control ATP-mediated Ca2+ signalling.