Fast and Reversible Stimulation of Astrocytic Glycolysis by K⁺ and a Delayed and Persistent Effect of Glutamate

Acute stimulation of astrocytic glycolysis by K⁺. A, The basal rate of glycolysis in a single astrocyte was first estimated over 2 min by applying 20 μm cytochalasin B, followed by addition of 12 mm K⁺. Dashed lines represent the rates before and after addition of K⁺. B, A similar experiment testing the effect of simultaneous addition of 50 μm glutamate and 12 mm K⁺. C, Transient exposure to 15 mm K⁺ brought about a fall in intracellular glucose, consistent with transient activation of glycolysis. Data are representative of 10 similar experiments. D, Glycolytic rate was measured in the presence of increasing concentrations of K⁺ (6 and 15 mm). E, Subsequent exposures of a cell to increasing K⁺ concentrations (2, 4, 6, 9, and 15 mm) caused stronger perturbations in glucose concentration. F, Intracellular glucose was measured every 2 s in cells with Fura 2, allowing nonquantitative reciprocal imaging of intracellular Ca²⁺ at 380 nm excitation (continuous line). The onset of the Fura 2 deflection (dotted vertical line) marked the arrival of 50 μm glutamate/15 mm K⁺ to the cell. The intercept between linear regressions before and after the Fura 2 deflection (dashed lines) was computed as the onset of metabolic activation. The difference between the Fura 2 deflection and the intercept was computed as the stimulation delay, which for this specific cell was zero. G, Lactate release by pure astrocytic cultures was measured over a period of 20 min in 3 mm K⁺ (control) or 15 mm K⁺ (n = 3 experiments paired with Fig. 1F). H, The rate of glucose metabolism in a single astrocyte in an organotypic hippocampal slice was measured with 20 μm cytochalasin B before and after exposure to 15 mm K⁺. Similar results were obtained in other eight experiments. I, Effect of 15 mm K⁺ on the concentration of glucose in an astrocyte, representative of five similar experiments.