Decreased glutamate metabolism in cultured astrocytes in the presence of thiopental

The effect of thiopental on glutamate metabolism was studied by C-13 magnet ic resonance spectroscopy. Cerebral cortical astrocytes were incubated with 0.5 mM [U-C-13]glutamate for 2 hr in the presence of 0.5 or 1 mM thiopenta l. Labeled glutamate, glutamine, aspartate, and glutathione were observed i n cell extracts, and glutamine, aspartate, and lactate in the medium. Nor. only present in the medium was uniformly labeled glutamate, but also glutam ate derived from the tricarboxylic acid (TCA) cycle, and thus glutamate rel ease could be detected. The amounts of [U-C-13]glutamate and unlabeled gluc ose taken up by astrocytes were unchanged in the presence of 0.5 mM thiopen tal and decreased to about 50% and 80%, respectively when the concentration was increased to 1 mM. The amounts of most metabolites synthesized from [U -C-13]glutamate were unchanged in the presence of 0.5 mM thiopental, but de creased [U-C-13]glutamine, [U-C-13]aspartate, and [U-C-13]lactate were obse rved in the 1 mM group. Surprisingly, the amounts of [1,2,3-C-13]glutamate, [2,3-C-13]aspartate, and [3,4-C-13]aspartate (2nd turn via the TCA cycle) were unchanged. However, this was not the case for [1,2-C-13]lactate and [2 ,3-C-13]lactate. Such variations indicate cellular compartmentation, possib ly caused by a heterogeneous glutamate concentration within the cells affec ting TCA cycle turnover rates differently. (C) 1999 Elsevier Science Inc.