Representative traces of [Ca2+]i response in solitary neurons and astrocytes in low density cultures stimulated with 30 μM UTP (A); 100 μM ATP (B). The traces shown are from a single neuron and astrocyte representing 15 neurons and 40 astrocytes from eight experiments. (C and D) Confocal images of mixed hippocampal cultures immunostained with anti-P2Y receptors (green) and synaptophysin (red). P2Y2 and P2Y4 receptors are expressed only in astrocytes. P2Y2 and P2Y4 receptor immunofluorescence was not colocalized with synaptophysin fluorescence at synaptic terminals.