LACTATE METABOLISM IN MOUSE-BRAIN ASTROCYTES STUDIED BY [C-13]NMR SPECTROSCOPY

ASTROCYTES possess at least two pathways for pyruvate and thus lactate formation involving precursors derived from mitochondria. The present results suggest that malic enzyme is the preferred route for this pro cess. Although overall lactate release appeared to be independent of e xtracellular lactate concentration, the incorporation of mitochondrial precursors was decreased by starvation, which is known to deplete ast rocyte glycogen stores. Using 1-[C-13]glucose in the presence of 10 mM lactate led to label incorporation into extracellular lactate which i ncreased from 3.4 +/- 0.4 to 6.5 +/- 0.5% during 4 and 6 h incubation periods, respectively. Lactate production from glycolysis proceeded vi rtually unaffected by the extracellular lactate concentration. The tot al amount of lactate in the medium decreased, however, demonstrating t hat lactate was used as a substrate.