Abstract
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
3
H
-
d-aspartate (
3
H
-
d-Asp) uptake with an IC
50 of 319 μM (
K
i=36.6 μM). In contrast, it did not prevent
d-aspartate-induced
3
H
-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 IC
50 of 47.7 μM and showed kinetic characteristics consistent with a mechanism of
trans-inhibition. Preincubation with THA also inhibited
d-aspartate-induced
3
H
-2DG uptake in a concentration-dependent manner with an apparent IC
50 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.