Effect of methylmercury on glutamate metabolism in cerebellar astrocytes in culture

The effect of methylmercury (MeHg) on [U-¹³C]glutamate metabolism was studied in cerebellar astrocytes using ¹³C nuclear magnetic resonance spectroscopy. The cells were preincubated in medium containing 25 or 50μM MeHg and 10% fetal calf serum for 4h and then in medium with [U-¹³C]glutamate (0.5mM) for 2h. Labeled glutamate, glutamine and aspartate were observed both in the cell extracts and media, labeled glutathione in the cell extracts and labeled lactate and alanine in the media. The amount of glutamate removed from the media was decreased in the 50μM MeHg group, furthermore, the levels of both labeled and unlabeled glutamine were decreased. This might indicate a decreased synthesis and/or increased degradation. An increase was observed for glutathione in the 25μM group, which might be due to an upregulated synthesis of glutathione in response to the toxic effects of MeHg. The percentage of [U-¹³C]glutamate used for the synthesis of metabolites via the tricarboxylic acid cycle was increased in the presence of 50μM MeHg. However, the percentage used for energy production was decreased in both groups, indicating selective mitochondrial vulnerability due to the inhibitory effect of MeHg.