COMPARTMENTATION OF LACTATE AND GLUCOSE-METABOLISM IN C6 GLIOMA-CELLS- A C-13 AND H-1-NMR STUDY

C-13 and H-1 NMR spectroscopy was used to investigate the metabolism o f L-lactate and D-glucose in C6 glioma cells, The changing of lactate and glucose concentration in the extracellular medium of C6 glioma cel ls incubated with 5.5 mM glucose and 11 mM lactate indicated a net pro duction of lactate as the consequence of an active aerobic glycolysis. The C-13 enrichments of various metabolites were determined after 4-h cell incubation in media containing both substrates, each of them bei ng alternatively labeled in the form of either [3-C-13]L-lactate or [1 -C-13]D-glucose. Using 11 mM [3-C-13]L-lactate, the enrichment of glut amate C4, 69%, was found higher than that of alanine C3, 32%, when tha t of acetyl-CoA C2 was 78%. These results indicated that exogenous lac tate was the major substrate for the oxidative metabolism of the cells , Nevertheless, an active glycolysis occurred, leading to a net lactat e production. This lactate was, however, metabolically different from the exogenous lactate as both lactate species did not mix into a uniqu e compartment, The results were actually consistent with the concept o f the existence of two pools of both lactate and pyruvate, wherein one pool was closely connected with exogenous lactate and was the main fu el for the oxidative metabolism, and the other pool was closely relate d to aerobic glycolysis.