Analysis of carbon metabolism in cultured cerebellar and cortical astrocytes

Carbon metabolism was investigated in cerebellar and cortical astrocytes cultured for 15 or 35 days. The consumption rates of exogenous carbon sources--amino acids and glucose--and the production rates of exported metabolites--citrate, lactate, alanine and glutamine--were determined. The specific 13C-enrichment of lactate and glutamine carbons were determined after cell incubation with [1-13C]glucose. These data were used to evaluate the fluxes through metabolic pathways using a monocompartmental model of the cell metabolism including glycolysis and tricarboxylic acid cycle related pathways. The model concluded to a very large contribution of fatty acids as an endogenous carbon source of acetyl-CoA. As a consequence of the high fatty acid turn-over, there was an important recycling (via pyruvate) of the oxaloacetate molecules generated by citrate lyase activity. This recycling represented in fact the major part of the pyruvate carboxylase activity, which therefore was not directly related to metabolite export. Comparing the data from cerebellar and cortical astrocytes evidenced, on the other hand, some differences in metabolite contents which could be related to different cell maturation stages linked to their different tissular origins.