Duan Shumin, Anderson Christopher M, Keung Edmund C, Chen Yongmei, Chen Yiren, Swanson Raymond A
Department of Neurology, University of California, San Francisco and Veterans Affairs Medical Center, San Francisco, California 94121, USA.
J Neurosci. 2003 Feb 15;23(4):1320-8. doi: 10.1523/JNEUROSCI.23-04-01320.2003.
Astrocyte glutamate release can modulate synaptic activity and participate in brain intercellular signaling. P2X7 receptors form large ion channels when activated by ATP or other ligands. Here we show that P2X7 receptors provide a route for excitatory amino acid release from astrocytes. Studies were performed using murine cortical astrocyte cultures. ATP produced an inward current in patch-clamped astrocytes with properties characteristic of P2X7 receptor activation: the current was amplified in low divalent cation medium, blocked by pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), and more potently activated by 3'-O-(4-benzoyl)benzoyl ATP (BzATP) than by ATP itself. Measurement of current reversal potentials showed the relative BzATP-induced permeabilities to different substrates to be Na+, 1 > Cl-, 0.34 > N-methyl-D-glucamine, 0.27 > L-glutamate, 0.15 approximately D-aspartate, 0.16. Astrocytes exposed to BzATP also became permeable to Lucifer yellow, indicating a large channel opening. Release of L-glutamate and D-aspartate through P2X7 channels was confirmed using radiolabeled tracers. As with the inward current, release of glutamate and D-aspartate was induced by BzATP more potently than ATP, amplified in Ca2+/Mg2+-free medium, and blocked by PPADS or oxidized ATP. Efflux through P2X7 channels is a previously unrecognized route of ligand-stimulated, nonvesicular astrocyte glutamate release.
星形胶质细胞释放谷氨酸可调节突触活动并参与脑内细胞间信号传导。P2X7受体在被ATP或其他配体激活时会形成大的离子通道。在此我们表明，P2X7受体为星形胶质细胞释放兴奋性氨基酸提供了一条途径。研究是使用小鼠皮质星形胶质细胞培养物进行的。ATP在膜片钳记录的星形胶质细胞中产生内向电流，其特性具有P2X7受体激活的特征：该电流在低二价阳离子培养基中被放大，被磷酸吡哆醛 - 6 - 偶氮苯 - 2',4'-二磺酸（PPADS）阻断，并且被3'-O-(4-苯甲酰基)苯甲酰基ATP（BzATP）比ATP本身更有效地激活。电流反转电位的测量表明，BzATP诱导的对不同底物的相对通透性为Na +，1＞Cl -，0.34＞N - 甲基 - D - 葡糖胺，0.27＞L - 谷氨酸，0.15≈D - 天冬氨酸，0.16。暴露于BzATP的星形胶质细胞对荧光黄也变得通透，表明有大通道开放。使用放射性标记示踪剂证实了通过P2X7通道释放L - 谷氨酸和D - 天冬氨酸。与内向电流一样，谷氨酸和D - 天冬氨酸的释放被BzATP比ATP更有效地诱导，在无Ca2 + /Mg2 +的培养基中被放大，并被PPADS或氧化ATP阻断。通过P2X7通道的外流是配体刺激的、非囊泡性星形胶质细胞谷氨酸释放的一条先前未被认识的途径。
