Fig. 2.

Time- and concentration-dependent consumption of extracellular pyruvate by primary astrocyte cultures. The cells were incubated for up to 5 h in a glucose-free incubation buffer with pyruvate in the concentrations indicated. The extracellular concentration of pyruvate (a) and the extracellular LDH activity (b) were determined for the time periods given. The almost linear decline in the extracellular pyruvate concentrations during the first 3 h of incubation was used to calculate the specific pyruvate consumption rates. The initial cellular LDH activity of the cultures was 116 ± 9 nmol/(min × well) and the initial protein content was 122 ± 7 µg/well (c). Half-maximal pyruvate consumption (as calculated by using the Michaelis-Menten equation) was observed for an initial pyruvate concentration of 0.6 ± 0.1 mM and the maximal pyruvate consumption rate was calculated to be 5.1 ± 0.8 nmol/(min × mg). The data shown are means ± SD of values obtained in three experiments performed on independently prepared cultures