Figure 5
Metabolic trafficking between astrocytes and neurons. À: Synaptic activity causes an accumulation of glutamate in the synaptic cleft. Á: An astrocytic glutamate transporter ensures removal of glutamate from the synaptic cleft. Â: The entry of Na+ cotransported with glutamate activates the Na+,K+-ATPase hence decreasing ATP levels. Ã: The decrease in ATP levels activates the glycolytic flux (see Fig. 1) hence stimulating glucose uptake from the capillaries. Ä: Lactate, the major end product of glycolysis, is released by astrocytes and taken up by neurons where it can enter the TCA cycle. Other metabolic intermediates such as pyruvate and the TCA cycle intermediates malate, citrate, and a-ketoglutarate, although quantitatively less significant, may also be released. Å: Certain neurotransmitter systems such as those containing NE and VIP promote glycogenolysis hence supplying further glycosyl residues for glycolysis. N, Neuron; A, astrocyte, C, capillary; Glu, glutamate; a-KG, a-ketoglutarate; DAG, diacylglycerol; Vm, depolarization of glutamate-containing terminal.
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published 2000