Fig. 4
Metabolic water production in activated astrocytes. Rapid fluctuations in brain activity trigger an increase in astrocyte metabolism associated with glutamate uptake, conversion of glutamate to glutamine, and the associated cation pumping. Astrocytic energy requirements are met by glycogenolysis, a pathway that can rapidly replenish ATP [46]. Glycolytic metabolism of 1 glucose-6-phosphate (Glc-6P) molecule produces 3 ATP, 1 of which replaces that used to produce fructose-1,6-bisphosphate (Fru-1,6P2). The other 2 ATP plus 2 glycolytic H2O are assigned to cation pumping; no metabolic water is available for secretion. Metabolic water production is twice the rate of glycogenolysis. The pyruvate (Pyr) generated from glycogen is converted to lactate (Lac) that is released from the cell