Presynaptic Release of Glutamate by Heteroexchange Under Altered Gravity Conditions

The study focused on the release of glutamate by reversal of Na (+) -dependent glutamate transporters that was investigated in cortical synaptosomes isolated from Wistar rats subjected to centrifuge-induced hypergravity of 10xg for 1 h. Transportable competitive inhibitor of glutamate transporters-DL-threo-beta-hydroxyaspartate (DL-THA) induced the release of L-[C-14]glutamate via heteroexchange that consisted of 22.5 +/- 1.7% of total label in normal gravity and 23.7 +/- 1.7% in altered gravity conditions. Inhibition of the ability of synaptic vesicles to accumulate the neuromediator by preliminary treatment of synaptosomes with the protonophore (FCCP) augmented the release of cytosolic L-[C-14]glutamate evoked by DL-THA from 44.0 +/- 2.0% to 52.0 +/- 2.3% of total label for G-loaded animals as compared to controls. Thus, combined application of DL-THA and FCCP revealed the increase in transporter-mediated release of glutamate that might be evidence for hypoxic injury of neurons.