Energetic and morphological plasticity of C6 glioma cells grown on 3-D support; Effect of transient glutamine deprivation

The energetic metabolism of rat C6 glioma cells has been investigated as a function of the proliferative and differentiation states under three-dimens ional (3-D) growing conditions on microcarrier beads. First, the transient deprivation of glutamine from the culture medium induced a marked decrease in the growth rate and a differentiation of C6 cells through the oligodendr ocytic phenotype. Second, the respiratory capacity of the C6 cells during s hortterm subcultures with or without glutamine continuously declined as a f unction of the cell density, in part due to the mitochondrial content decre ase. During the transition from the early exponential to the plateau growth phase in glutamine-containing medium, the oxygen consumption rate per sing le cell decreased concomitantly with a decrease in the glucose consumption and lactate production rates. This phenomenon led to a sixfold decrease in the total ATP production flux, without significantly affecting the cellular ATP/ADP ratio, thus indicating that some ATP-consuming processes were simu ltaneously suppressed during C6 proliferation. In glutamine-free medium, th e cellular ATP/ADP ratio transiently increased due to growth arrest and to a reduced ATP turnover. Moreover, the results indicated that glutamine is n ot an essential respiratory substrate for rat C6 glioma under short-term gl utamine deprivation. Worth noting was the high contribution of the mitochon drial oxidative phosphorylation toward the total ATP synthesis (about 80%), regardless of the proliferation or the differentiation status of the C6 ce lls.