Differential frequency dependence of P2Y1- and P2Y2- mediated Ca 2+ signaling in astrocytes.

ATP is a key extracellular messenger that mediates the propagation of Ca 2+ waves in astrocyte networks in various regions of the CNS. ATP-mediated Ca 2+ signals play critical roles in astrocyte proliferation and differentiation and in modulating neuronal activity. The actions of ATP on astrocytes are via two distinct subtypes of P2Y purinoceptors, P2Y1 and P2Y2 receptors (P2Y1Rs and P2Y2Rs), G-protein coupled receptors that stimulate mobilization of intracellular Ca 2+ ([Ca 2+]i) via the phospholipase Cbeta-IP3 pathway. We report here that P2Y1R-mediated and P2Y2R-mediated Ca 2+ responses differentially show two forms of activity-dependent negative feedback. First, Ca 2+ responses mediated by either receptor exhibit slow depression that is independent of stimulation frequency. Second, responses mediated by P2Y1Rs, but not those mediated by P2Y2Rs, 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 Thr339 in the C terminus of P2Y1R. We propose that frequency-dependent changes in ATP-mediated Ca 2+ signaling pathways may modulate astrocyte function and astrocyte-neuron signaling in the CNS.