Pumain R, Kurcewicz I, Louvel J
Can J Physiol Pharmacol. 1987 May;65(5):1067-77. doi: 10.1139/y87-168.
The ionic mechanisms underlying the action of excitatory amino acids were investigated in the rat motor cortex. Ion-selective microelectrodes were attached to micropipettes such that their tips were very close and local changes in extracellular concentration of sodium, calcium, and potassium ions elicited through ionophoretic applications of glutamate (Glu) and of its agonists N-methyl-D-aspartate (NMDA), quisqualate (Quis), and kainate (Ka) were measured. These agents produced moderate increases in [K+]o (up to 13 mM) but, in contrast, substantial tetrodotoxin-insensitive decreases in [Na+]o (maximally of 60 mM). NMDA-induced sodium responses could be blocked by manganese, while the Quis- and Ka-induced responses were not. Quis and Ka produced increases in [Ca2+]o or biphasic responses while NMDA, even with small doses, induced each time drastic decreases in [Ca2+]o (maximally of 1.15 mM), which could be attenuated or blocked by manganese but not by organic calcium channel blockers. NMDA responses could be abolished by reduced doses of 2-amino-phosphonovalerate. The largest Glu- and NMDA-induced calcium responses were observed in the superficial cortical layers, but such maxima disappeared after selective degeneration of pyramidal tract neurons. All amino acids produced sizeable reductions in the extracellular space volume. The following can be concluded. (i) All the excitatory amino acids tested induce an increased permeability to sodium and potassium ions. (ii) In addition, the NMDA-operated channels have specifically a large permeability for calcium, although calcium ions contribute only by less than 10% to the NMDA-induced inward currents.(ABSTRACT TRUNCATED AT 250 WORDS)
在大鼠运动皮层中研究了兴奋性氨基酸作用的离子机制。将离子选择性微电极连接到微量移液器上，使它们的尖端非常靠近，并测量通过离子电泳应用谷氨酸（Glu）及其激动剂N-甲基-D-天冬氨酸（NMDA）、quisqualate（Quis）和海人藻酸（Ka）引起的细胞外钠、钙和钾离子浓度的局部变化。这些试剂使[K⁺]o适度增加（高达13 mM），但相比之下，[Na⁺]o却有大量对河豚毒素不敏感的降低（最大降低60 mM）。NMDA诱导的钠反应可被锰阻断，而Quis和Ka诱导的反应则不能。Quis和Ka使[Ca²⁺]o增加或产生双相反应，而NMDA即使小剂量也每次都诱导[Ca²⁺]o急剧降低（最大降低1.15 mM），这可被锰减弱或阻断，但不能被有机钙通道阻滞剂阻断。NMDA反应可被降低剂量的2-氨基-膦酸戊酸消除。在皮层浅层观察到最大的Glu和NMDA诱导的钙反应，但在锥体束神经元选择性变性后这种最大值消失。所有氨基酸都使细胞外空间体积大幅减小。可以得出以下结论。（i）所有测试的兴奋性氨基酸都诱导对钠和钾离子的通透性增加。（ii）此外，NMDA操作的通道对钙具有特别大的通透性，尽管钙离子对NMDA诱导的内向电流的贡献仅不到10%。（摘要截断于250字）
