Activation of P2X7 receptors decreases glutamate uptake and glutamine synthetase activity in RBA-2 astrocytes via distinct mechanisms.

Glutamate clearance by astrocytes is critical for controlling excitatory neurotransmission and ATP is an important mediator for neuron-astrocyte interaction. However, the effect of ATP on glutamate clearance has never been examined. Here we report that treatment of RBA-2 cells, a type-2-like astrocyte cell line, with ATP and the P2X7 receptor selective agonist 3′-O-(4-benzoylbenzoyl) adenosine 5′-triphosphate (BzATP) decreased the Na+-dependent [3H]glutamate uptake within minutes. Mechanistic studies revealed that the decreases were augmented by removal of extracellular Mg2+ or Ca2+, and was restored by P2X7 selective antagonist , periodate-oxidized 2′,3′-dialdehyde ATP (oATP), indicating that the decreases were mediated through P2X7 receptors. Furthermore, stimulation of P2X7 receptors for 2 h inhibited both activity and protein expression of glutamine synthetase (GS), and oATP abolished the inhibition. In addition, removal of extracellular Ca2+ and inhibition of protein kinase C (PKC) restored the ATP-decreased GS expression but failed to restore the P2X7-decreased [3H]glutamate uptake. Therefore, P2X7-mediated intracellular signals play a role in the down-regulation of GS activity/expression. Activation of P2X7 receptors stimulated increases in intracellular Na+ concentration ([Na+]i) suggesting that the P2X7-induced increases in [Na+]i may affect the local Na+ gradient and decrease the Na+-dependent [3H]glutamate uptake. These findings demonstrate that the P2X7-mediated decreases in glutamate uptake and glutamine synthesis were mediated through distinct mechanisms in these cells. [ABSTRACT FROM AUTHOR]