Trans-inhibition of glutamate transport prevents excitatory amino acid-induced glycolysis in astrocytes

Previous studies have demonstrated that activation of glutamate transporters promotes glycolysis in astrocytes. Current evidence indicates that compounds such as threo-β-hydroxyaspartate (THA) are both competitive inhibitors and substrates for glutamate transporters. In this study, we have analyzed the effect of THA on excitatory amino acid (EAA) transport and on EAA-induced glycolysis in mouse primary astrocyte cultures. In agreement with previous studies in rat astrocytes, THA competitively inhibited ³H-D-aspartate (³H-D-Asp) uptake with an IC₅₀ of 319 μM (K(i)=36.6 μM). In contrast, it did not prevent D-aspartate-induced ³H-2-deoxyglucose (2DG) uptake in these conditions. Preexposure of cells to THA for at least 15 min revealed another form of glutamate transport inhibition. This effect was concentration-dependent with an apparent IC₅₀ of 47.7 μM and showed kinetic characteristics consistent with a mechanism of trans-inhibition. Preincubation with THA also inhibited D-aspartate-induced ³H-2DG uptake in a concentration-dependent manner with an apparent IC₅₀ of 59.8 μM. Comparison with other transportable analogues reveals that they share with THA the ability to cause trans-inhibition of glutamate transport and to prevent glutamate-stimulated glycolysis; THA, however, is unique in that it has no effect alone on glucose utilization after preexposure. These data indicate that trans-inhibition of glutamate transport may be a mechanism by which certain glutamate transport inhibitors can prevent the stimulation of aerobic glycolysis by glutamate in astrocytes. Copyright (C) 1999 Elsevier Science B.V.