Ouabain‐induced reversal of astrocytic GLT‐1 crucial to neuronal death in neuron/astrocyte co‐cultures

We investigated whether the role of the astrocytic glutamate transporter GLT-1 is reversed when the ionic gradient across plasma membrane has collapsed, and if so, whether the reversal is crucial to neuronal death. To estimate the direction of glutamate transport by GLT-1, Na+ movement coupled with glutamate transport in astrocytes was analyzed in mixed astrocyte/neuron cultures. The rise in astrocytic intracellular Na+ due to glutamate exposure was suppressed by co-treatment with dihydrokainate (DHK). In contrast, the ouabain-induced rise in Na+ was significantly enhanced by DHK, suggesting that the role of GLT-1 was reversed. We then analyzed whether the reversal increased the amount of extracellular glutamate, and was crucial to excitotoxic neuronal death. Ouabain treatment resulted in a marked rise in glutamate and in neuronal death, and both the rise and cell death were significantly attenuated by DHK treatment.