Differential frequency dependence of P2Y1- and P2Y2-mediated Ca2+ signaling in astrocytes

ATP is a key extracellular messenger that mediates the propagation of Ca2+ waves in astrocyte networks in various regions of the CNS. ATP-mediated Ca2+ signals play critical roles in astrocyte proliferation and differentiation and in modulating neuronal activity. The actions ofATPon astrocytes are via two distinct subtypes of P2Y purinoceptors, P2Y(1) and P2Y(2) receptors ( P2Y(1)Rs and P2Y(2)Rs), G-protein coupled receptors that stimulate mobilization of intracellular Ca2+([Ca2+](i)) via the phospholipase Cbeta- IP3 pathway. We report here that P2Y(1)R-mediated and P2Y(2)R-mediated Ca2+ responses differentially show two forms of activity-dependent negative feedback. First, Ca2+ responses mediated by either receptor exhibit slow depression that is independent of stimulation frequency. Second, responses mediated by P2Y(1)Rs, but not those mediated by P2Y(2)Rs, show rapid oscillations after high-frequency stimulation. We demonstrate that the oscillations are mediated by recruiting negative feedback by protein kinase C, and we map the site responsible for the effect of protein kinase C to Thr(339) in the C terminus of P2Y(1)R. We propose that frequency-dependent changes in ATP-mediated Ca2+ signaling pathways may modulate astrocyte function and astrocyte - neuron signaling in the CNS.