Glutamate receptor agonists up-regulate glutamate transporter GLAST in astrocytes

LONG-TERM treatment of astrocytes in primary culture with L-glutamate (0.1–3 mM) resulted in a dose-dependent increase in D-[H]aspartate uptake. The effect was abolished by an antagonist of kainate/AMPA receptors, CNQX, and mimicked by kainate, but not by AMPA or tACPD. Both glutamate and kainate caused a dramatic up-regulation (82% and 69%, respectively) of GLAST, a predominant glutamate transporter in cultured astroglia, though the mRNA levels appeared unaffected. Long-term treatment of cultures with dBcAMP stimulated D-[H]aspartate uptake as well as GLAST expression. Apart from glutamate, none of the agonists used was capable of increasing further the uptake capacity of the dBcAMP-treated astroglia. The glutamate receptor- dependent modulation of glutamate transport in astroglial cultures may represent a novel feedback regulatory mechanism for glutamate uptake in the brain.