Functional hemichannels in astrocytes: A novel mechanism of glutamate release
Functional hemichannels in astrocytes: A novel mechanism of glutamate release
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DOI：
10.1523/jneurosci.23-09-03588.2003
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发表时间：
2003-05-01
影响因子：
5.3
通讯作者：
Ransom, BR
中科院分区：
文献类型：
--
作者：
Ye, ZC;Wyeth, MS;Ransom, BR
关于无对抗间隙连接半通道在脑中的表达和可能的功能知之甚少。新出现的证据表明，缝隙连接半通道可以作为星形胶质细胞中的独立功能通道。免疫细胞化学，染料摄取，和HPLC测量，我们表明，星形胶质细胞在体外表达功能性半通道，可以介导强大的流出谷氨酸和天冬氨酸。通过在标称二价无阳离子溶液（DCFS）中细胞外荧光黄（LY）进入星形胶质细胞以及用间隙连接阻断剂阻断该通道的能力来证实功能性半通道。DCFS中的谷氨酸/天冬氨酸释放（或LY加载）被多价阳离子（Ca 2+、Ba 2+、Sr 2+、Mg 2+和La 3+）和间隙连接阻断剂（甘珀酸、辛醇、庚醇、氟灭酸和18 α-大黄酸）阻断，其亲和力接近于报道的间隙连接细胞间通讯阻断剂。通过半通道的谷氨酸流出也伴随着谷氨酸摄取大大减少。谷氨酸释放DCFS，但是，没有显着介导的逆转谷氨酸转运蛋白：释放不饱和，不被谷氨酸转运蛋白阻断剂。DCFS中的对照实验排除了通过体积敏感性阴离子通道、P2 X（7）嘌呤能受体孔或一般嘌呤能受体激活释放谷氨酸。BAPTA-AM或毒胡萝卜素阻断细胞内Ca ~（2+）动员并不能抑制DCFS中谷氨酸的释放。二价阳离子去除还诱导完整的中枢神经系统白色物质（急性分离的视神经）释放谷氨酸，该物质被甘珀酸阻断，这表明原位存在功能性半通道。我们的研究结果表明，星形胶质细胞半通道可以影响中枢神经系统的细胞外谷氨酸水平与正常和病理性脑功能的影响。
Little is known about the expression and possible functions of unopposed gap junction hemichannels in the brain. Emerging evidence suggests that gap junction hemichannels can act as stand-alone functional channels in astrocytes. With immunocytochemistry, dye uptake, and HPLC measurements, we show that astrocytes in vitro express functional hemichannels that can mediate robust efflux of glutamate and aspartate. Functional hemichannels were confirmed by passage of extracellular lucifer yellow (LY) into astrocytes in nominal divalent cation-free solution (DCFS) and the ability to block this passage with gap junction blocking agents. Glutamate/aspartate release (or LY loading) in DCFS was blocked by multivalent cations (Ca2+, Ba2+, Sr2+, Mg2+, and La3+) and by gap junction blocking agents (carbenoxolone, octanol, heptanol, flufenamic acid, and 18alpha-glycyrrhetinic acid) with affinities close to those reported for blockade of gap junction intercellular communication. Glutamate efflux via hemichannels was also accompanied by greatly reduced glutamate uptake. Glutamate release in DCFS, however, was not significantly mediated by reversal of the glutamate transporter: release did not saturate and was not blocked by glutamate transporter blockers. Control experiments in DCFS precluded glutamate release by volume-sensitive anion channels, P2X(7) purinergic receptor pores, or general purinergic receptor activation. Blocking intracellular Ca2+ mobilization by BAPTA-AM or thapsigargin did not inhibit glutamate release in DCFS. Divalent cation removal also induced glutamate release from intact CNS white matter ( acutely isolated optic nerve) that was blocked by carbenoxolone, suggesting the existence of functional hemichannels in situ. Our results indicated that astrocyte hemichannels could influence CNS levels of extracellular glutamate with implications for normal and pathological brain function.