Figure 4. Schematic presentation of multiple compartments in astrocytes.

Synthesis of a large amount of releasable citrate via pyruvate carboxylase occurs in compartment A, a compartment for preferential glucose metabolism. Releasable glutamine is synthesized from glutamate originating from compartments B and C. Glucose is the main oxidative substrate for compartment B, whereas lactate and glucose are metabolized to the same extent in compartments C and D. The main intracellular pool of glutamine is synthesized from glutamate originating from compartment D. The size of the arrows provide an estimate of the relative magnitudes of the respective fluxes. GLN, glutamine; GLU, glutamate; CIT, citrate; OAA, oxaloacetate; ASP, aspartate; FUM, fumarate.