Figure 8. Astrocytes have high capacity for rapid lactate uptake and lactate dispersal to other gap junction-coupled astrocytes compared with neuronal lactate uptake and astrocyte-to-neuron lactate shuttling.

Initial (A, B) and net (C, D) rates of lactate uptake from an extracellular point source into astrocytes and neurons at different lactate concentrations. Initial (E, F) and net (G, H) rates of lactate transfer from an astrocyte to another astrocyte or to a neuron located the same distance from the donor astrocyte as the gap junction-coupled recipient astrocyte. Figure re-printed from Gautam K. Gandhi, Nancy F. Cruz, Kelly K. Ball, Gerald A. Dienel (2009) Astrocytes are poised for lactate trafficking and release from activated brain and for supply of glucose to neurons, Journal of Neurochemistry 111:522–536. published by John Wiley and Sons © 2009 The Authors. Journal Compilation © 2009 International Society for Neurochemistry. When the extracellular lactate level approximates the mean tissue lactate level during brain activation (2 mmol/l), lactate uptake into astrocytes and lactate shuttling among astrocytes is about twice that of neurons, and the difference is larger as the lactate level rises. Astrocyte-to-neuron lactate shuttling does not change with increasing lactate level, even as high as 10 mmol/l in the donor astrocyte. Shuttling of lactate to neurons is much less than that dispersed to another astrocyte, and thousands of astrocytes are gap junction coupled.