Kriegler S, Chiu S Y
Biophysics Training Program, University of Wisconsin, Madison 53706.
J Neurosci. 1993 Oct;13(10):4229-45. doi: 10.1523/JNEUROSCI.13-10-04229.1993.
Glial [Ca2+]i signaling was examined in a mammalian white matter lacking neuronal cell bodies and synapses. Rat optic nerves (postnatal days 2 and 7) were stained with calcium indicator dyes and confocal images of [Ca2+bdi were recorded at approximately 25 degrees C or approximately 37 degrees C. Glial cell bodies showed spiking or sustained [Ca2+], response to bath-applied glutamate (50-500 microM). The metabotropic glutamate agonist trans-ACPD elicited transient, sometimes spiking, [Ca2+], responses, whereas ionotropic agonists kainate and AMPA elicited a 6,7-dinitroquinoxaline-2,3-dione-sensitive, mostly sustained [Ca2+]i response. Transient and spiking glial [Ca2+]i responses also were elicited by adenosine and ATP (0.1-100 microM). Repetitive nerve stimulation (10-20 Hz) elicited [Ca2+bdi spiking in 15-25% of glial cells in postnatal day 7 nerves, with spiking typically occurring 15-60 sec after onset of nerve stimulation. At 37 degrees C, the frequency of glial [Ca2+]i spikes increased from approximately 0.06 Hz to approximately 0.11 Hz when axonal stimulation was increased from 10 to 20 Hz. This activity-dependent glial spiking was inhibited by TTX, could not be mimicked by increasing the bath K+ by 20 mM, and occurred when nerves were stimulated in the absence of bath calcium. Activity-dependent and glutamate-induced glial spiking could be mimicked by altering ionic gradients known to favor release of glutamate via glutamate transporters, including elevation of intracellular Na+ by veratridine concurrent with external K+ elevation. We suggest that glial [Ca2+]i spiking observed during electrical activity resulted from activation of glial receptors (e.g., metabotropic glutamate receptor, adenosine receptor) by substances (e.g., glutamate, adenosine) released from the optic nerve in a nonvesicular fashion, possibly through a reversal of sodium-coupled transporters when Na+ and K+ gradients are altered by prolonged nerve activity.
在缺乏神经元胞体和突触的哺乳动物白质中研究了胶质细胞内钙离子（[Ca2+]i）信号传导。用钙指示剂染料对大鼠视神经（出生后第2天和第7天）进行染色，并在约25℃或约37℃下记录[Ca2+]i的共聚焦图像。胶质细胞胞体对浴槽中施加的谷氨酸（50 - 500微摩尔）表现出尖峰状或持续性的[Ca2+]i反应。代谢型谷氨酸受体激动剂反式-ACPD引发短暂的、有时是尖峰状的[Ca2+]i反应，而离子型激动剂 kainate 和 AMPA 引发一种对 6,7 - 二硝基喹喔啉 - 2,3 - 二酮敏感的、大多为持续性的[Ca2+]i反应。腺苷和 ATP（0.1 - 100微摩尔）也能引发短暂的和尖峰状的胶质细胞[Ca2+]i反应。重复神经刺激（10 - 20赫兹）在出生后第7天的神经中，能使15 - 25%的胶质细胞产生[Ca2+]i尖峰，尖峰通常在神经刺激开始后15 - 60秒出现。在37℃时，当轴突刺激从10赫兹增加到20赫兹时，胶质细胞[Ca2+]i尖峰的频率从约0.06赫兹增加到约0.11赫兹。这种活动依赖性的胶质细胞尖峰受到河豚毒素（TTX）的抑制，不能通过将浴槽中的钾离子浓度增加20毫摩尔来模拟，并且在无浴槽钙的情况下刺激神经时也会出现。活动依赖性和谷氨酸诱导的胶质细胞尖峰可以通过改变已知有利于通过谷氨酸转运体释放谷氨酸的离子梯度来模拟，包括通过藜芦碱升高细胞内钠离子同时升高细胞外钾离子。我们认为，在电活动期间观察到的胶质细胞[Ca2+]i尖峰是由视神经以非囊泡方式释放的物质（如谷氨酸、腺苷）激活胶质细胞受体（如代谢型谷氨酸受体、腺苷受体）所致，可能是当钠离子和钾离子梯度因长时间神经活动而改变时，钠耦联转运体发生逆转的结果。
