Chatton J Y, Marquet P, Magistretti P J
Institute of Physiology and Laboratory of Neurological Research, Department of Neurology, University of Lausanne Medical School, Rue du Bugnon 7, CH-1005 Lausanne, Switzerland.
Eur J Neurosci. 2000 Nov;12(11):3843-53. doi: 10.1046/j.1460-9568.2000.00269.x.
The mode of Na+ entry and the dynamics of intracellular Na+ concentration ([Na+]i) changes consecutive to the application of the neurotransmitter glutamate were investigated in mouse cortical astrocytes in primary culture by video fluorescence microscopy. An elevation of [Na+]i was evoked by glutamate, whose amplitude and initial rate were concentration dependent. The glutamate-evoked Na+ increase was primarily due to Na+-glutamate cotransport, as inhibition of non-NMDA ionotropic receptors by 6-cyano-7-nitroquinoxiline-2,3-dione (CNQX) only weakly diminished the response and D-aspartate, a substrate of the glutamate transporter, produced [Na+]i elevations similar to those evoked by glutamate. Non-NMDA receptor activation could nevertheless be demonstrated by preventing receptor desensitization using cyclothiazide. Thus, in normal conditions non-NMDA receptors do not contribute significantly to the glutamate-evoked Na+ response. The rate of Na+ influx decreased during glutamate application, with kinetics that correlate well with the increase in [Na+]i and which depend on the extracellular concentration of glutamate. A tight coupling between Na+ entry and Na+/K+ ATPase activity was revealed by the massive [Na+]i increase evoked by glutamate when pump activity was inhibited by ouabain. During prolonged glutamate application, [Na+]i remains elevated at a new steady-state where Na+ influx through the transporter matches Na+ extrusion through the Na+/K+ ATPase. A mathematical model of the dynamics of [Na+]i homeostasis is presented which precisely defines the critical role of Na+ influx kinetics in the establishment of the elevated steady state and its consequences on the cellular bioenergetics. Indeed, extracellular glutamate concentrations of 10 microM already markedly increase the energetic demands of the astrocytes.
通过视频荧光显微镜技术，在原代培养的小鼠皮质星形胶质细胞中研究了神经递质谷氨酸作用后钠离子（Na⁺）的进入模式以及细胞内钠离子浓度（[Na⁺]i）变化的动力学过程。谷氨酸可诱发[Na⁺]i升高，其幅度和初始速率呈浓度依赖性。谷氨酸诱发的Na⁺增加主要归因于Na⁺-谷氨酸共转运，因为用6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）抑制非NMDA离子型受体只能微弱地减弱该反应，而谷氨酸转运体的底物D-天冬氨酸产生的[Na⁺]i升高与谷氨酸诱发的相似。然而，使用环噻嗪防止受体脱敏可证明非NMDA受体的激活。因此，在正常情况下，非NMDA受体对谷氨酸诱发的Na⁺反应贡献不大。在施加谷氨酸期间，Na⁺内流速率下降，其动力学与[Na⁺]i的增加密切相关，且取决于细胞外谷氨酸浓度。当哇巴因抑制泵活性时，谷氨酸诱发的大量[Na⁺]i增加揭示了Na⁺进入与Na⁺/K⁺ ATP酶活性之间的紧密耦合。在长时间施加谷氨酸期间，[Na⁺]i在一个新的稳态下保持升高，此时通过转运体的Na⁺内流与通过Na⁺/K⁺ ATP酶的Na⁺外流相匹配。本文提出了一个[Na⁺]i稳态动力学的数学模型，该模型精确地定义了Na⁺内流动力学在建立升高的稳态及其对细胞生物能量学影响方面的关键作用。实际上，10微摩尔的细胞外谷氨酸浓度已显著增加了星形胶质细胞的能量需求。
