Inhibitors of glutamate transport modulate distinct patterns in brain metabolism

Abstract

High affinity uptake of glutamate plays a major role in the termination of excitatory neurotransmission. Identification of the ramifications of transporter function is essential to understand the diseases in which defective excitatory amino acid transporters (EAAT) have been implicated. In this work we incubated Guinea pig cortical tissue slices with [3-(13)C]pyruvate and major currently available glutamate uptake inhibitors and studied the resultant metabolic sequelae by (13)C and (1)H NMR spectroscopy using a multivariate statistical approach. Perturbation of glutamate uptake produced significant effects on metabolic flux through the Krebs cycle, and on glutamate/glutamine cycling rates, with this effect accounting for 76% of the variation in the total data set. The effects of all inhibitors were separable from each other along three major principal components. The competitive inhibitor L-CCG III ((2S,1'S,2'R)-2-carboxycyclopropyl)glycine) differed most from the other inhibitors, showing negative weightings on both the first and second principal components, whereas the EAAT2-specific inhibitor dihydrokainate (DHK) showed metabolic patterns similar to that of anti-endo-3,4-methanopyrolidine dicarboxylate but separate from those of DL-threo-beta-benzyloxyaspartate (TBOA) and L-trans-pyrrolidine-2,4-dicarboxylate (L-tPDC). This indicates that different inhibition mechanisms or different colocalisation of the separate transporter subtypes with glutamate receptors can produce significantly different metabolic and functional outcomes for the brain.

Distribution of Glutamate Transporter GLAST in Membranes of Cultured Astrocytes in the Presence of Glutamate Transport Substrates and ATP

“…Such movements may occur in response to changes in the activity of glutamatergic synapses and, therefore, activity of L-glu transport could be of importance not only for the normal operation of the synaptic excitation [5] but also as an indicator of local excitatory activity that would have to be matched by local changes in the metabolism and blood flow. Indeed, it has recently been demonstrated that not only pharmacological manipulation of glutamate receptors but, in particular, interference with GluT, can elicit specific metabolic responses in brain tissue [14][15][16][17].…”

Rottlerin Inhibits (Na+, K+)-ATPase Activity in Brain Tissue and Alters d-Aspartate Dependent Redistribution of Glutamate Transporter GLAST in Cultured Astrocytes

“…)-dependent ATPase in brain tissue [13]. Such a relationship could be important for the regulation of energy supply in response to changes in excitatory (glutamatergic) synaptic activity [14,15] and for the activity of metabolic pathways that are linked to glutamatergic neurotransmission and/or to functioning glutamate transport [16][17][18]. Testing the effect of rottlerin on the activity of the (Na ?…”

GLAST But Not Least—Distribution, Function, Genetics and Epigenetics of l-Glutamate Transport in Brain—Focus on GLAST/EAAT1

“…Experiments with brain cortical tissue in vitro have indicated that inhibition of GluT (this would include GluT in glia, neurons as well as the ''presynaptic'' GluT) depended somewhat on the type of inhibitor used but, those compounds which are not transported themselves but clearly inhibit at least one of the main EAATs [32], appeared to potentiate glutamatergic activity [33,34]. This would seem to suggest that GluT has a primarily moderating effect on glutamatergic neurotransmission and would be consistent with the predominant role of GluT being that of limiting the spread of synaptically released L-Glu and preventing ''runaway'' excitation; if it was important mainly for replenishing presynaptic stores thus maintaining the potency of glutamatergic synapses, the effect of GluT inhibitors would not be expected to cause an increase in the overall intensity of glutamatergic excitation over a period of many minutes [33,34].…”