Glutathione restoration as indicator for cellular metabolism of astroglial cells

The restoration of glutathione in astroglia-rich primary cultures derived from the brains of newborn rats was used to indicate metabolic properties of astroglial cells. At a culture age of 14-21 days these cultures contain an average total glutathione content of 32.8 +/- 3.2 nmol/mg protein and a cytosolic volume, estimated with the 3-O-methylglucose method, of 4.1 +/- 0.1 microl/mg protein. Therefore, cells of astroglial cultures have a cytosolic glutathione concentration of about 8 mM. In order to investigate glutathione synthesis in astroglial cultures the cellular glutathione content was reduced by starvation in a minimal medium lacking glucose and amino acids. Resynthesis of glutathione depended on the presence of glucose and the three constituent amino acids glutamate, cysteine and glycine. Absence of glucose reduced the amount of net glutathione restoration found after 4 h of incubation by about 50%. Of known substrates of astroglial energy metabolism, mannose could fully and fructose, lactate, pyruvate or sorbitol could partially replace glucose during glutathione restoration. In contrast to these compounds, galactose, 5-thioglucose and 2-deoxyglucose failed to substitute for glucose during glutathione restoration. Astroglial cells are able to use as precursors for the three constituent amino acids of glutathione a variety of amino acids and dipeptides. The results presented demonstrate that glutathione restoration can be used as an indicator for amino acid as well as energy metabolism of astroglial cells.