Figure 3. Photolysis of caged Ca2+ triggers efflux of cytosolic glutamate via anion channels. A, Schematic drawing depicts that depletion of intracellular glutamate by addition of GPT and pyruvate to the pipette solution eliminates cytosolic glutamate (right). Representative traces of mEPSCs in a CA1 pyramidal neuron recorded during photolysis of NP-EGTA in a nearby astrocyte in which GPT and pyruvate was added to the patch pipette solution (left). B, Schematic drawing showing that addition of GPT, but not pyruvate (Pyru), to the pipette solution does not eliminates cytosolic glutamate (right). Representative traces of mEPSCs in a CA1 pyramidal neuron recorded during photolysis of NP-EGTA in a nearby astrocyte after addition of GPT, but not pyruvate, to the pipette solution (left). C, Histograms comparing the effects of addition of vehicle, GPT (100 U/L) and sodium pyruvate (1 mm), GPT alone, NPPB (50 μm), and DIDS (5 μm) to the pipette patching astrocytes on the amplitude of mEPSCs (p > 0.05, paired t test and one-way ANOVA; n = 5), frequency of mEPSCs (*p < 0.05, paired t test before and after photolysis for each group; #p < 0.01, one-way ANOVA with Bonferroni's test, comparing different pipette conditions; n = 5), and membrane potential changes (*p < 0.05, paired t test before and after photolysis for each group; #p < 0.05, one-way ANOVA with Bonferroni's test comparing different pipette conditions; n = 4–5) in CA1 neurons induced by a photolysis in neighboring astrocytes. D, Representative traces of recordings of mEPSCs in a pyramidal CA1 neuron in response to photolysis of NP-EGTA in a nearby astrocyte in a slice prepared from dnSNARE mice (−Dox indicates not receiving Dox). E, Histogram comparing the effects of photolysis of NP-EGTA in astrocytes on the amplitude (*p < 0.05, paired t test before and after photolysis for each group; #p < 0.05, t test comparing dnSNARE mice with or without Dox water; n = 5–6), frequency (*p < 0.05, paired t test before and after photolysis for each group; n = 5–6) of mEPSCs, and membrane potentials of neighboring neurons (*p < 0.05, paired t test before and after photolysis for each group; n = 5–6) in nearby neurons in slices prepared from +Dox (with Dox) and −Dox (without Dox).