Lo Jun-Chih, Huang Wei-Chi, Chou Yun-Chia, Tseng Chun-Hsien, Lee Wei-Li, Sun Synthia H
Institute of Neuroscience, National Yang Ming University, Taipei, Taiwan, Republic of China.
J Neurochem. 2008 Apr;105(1):151-64. doi: 10.1111/j.1471-4159.2007.05119.x. Epub 2007 Dec 6.
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 P2X(7) 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 P2X(7) 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 Ca(2+) and inhibition of protein kinase C (PKC) restored the ATP-decreased GS expression but failed to restore the P2X(7)-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+) suggesting that the P2X(7)-induced increases in Na+ 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.
星形胶质细胞清除谷氨酸对于控制兴奋性神经传递至关重要，而三磷酸腺苷（ATP）是神经元与星形胶质细胞相互作用的重要介质。然而，ATP对谷氨酸清除的影响从未被研究过。在此我们报告，用ATP和P2X(7)受体选择性激动剂3'-O-(4-苯甲酰苯甲酰)腺苷5'-三磷酸（BzATP）处理RBA-2细胞（一种2型样星形胶质细胞系），数分钟内可降低钠依赖性[3H]谷氨酸摄取。机制研究表明，去除细胞外镁离子或钙离子会增强这种降低，而P2X7选择性拮抗剂高碘酸盐氧化的2',3'-二醛ATP（oATP）可使其恢复，这表明这种降低是通过P2X(7)受体介导的。此外，刺激P2X7受体2小时可抑制谷氨酰胺合成酶（GS）的活性和蛋白表达，而oATP可消除这种抑制。另外，去除细胞外钙离子和抑制蛋白激酶C（PKC）可恢复ATP降低的GS表达，但未能恢复P2X(7)降低的[3H]谷氨酸摄取。因此，P2X7介导的细胞内信号在GS活性/表达的下调中起作用。P2X7受体的激活刺激细胞内钠离子浓度（Na+）升高，这表明P2X(7)诱导的Na+升高可能影响局部钠离子梯度并降低钠依赖性[3H]谷氨酸摄取。这些发现表明，P2X7介导的谷氨酸摄取和谷氨酰胺合成的降低在这些细胞中是通过不同机制介导的。
