Ferreira I L, Duarte C B, Carvalho A P
Center for Neurosciences of Coimbra, Department of Zoology, University of Coimbra, Portugal.
Eur J Pharmacol. 1996 Apr 29;302(1-3):153-62. doi: 10.1016/0014-2999(96)00044-1.
We studied the effect of glutamate, N-methyl-D-aspartate (NMDA), kainate or K+ depolarization, on neurotoxicity in cultured chick retinal cells, under conditions in which we could discriminate between Ca2+ entering through ionotropic glutamate receptors and voltage-sensitive Ca2+ channels (VSCCs). When neurons were challenged with NMDA, kainate or glutamate, in Na(+)-containing medium, a decrease in cell survival was observed, whereas K+ depolarization did not affect the viability of the cells. The Mg2+ ion completely prevented the toxic effect mediated by the NMDA receptor, and had a small but significant protective effect at the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate (AMPA/kainate) receptor-induced cell death. We observed that, in a Na(+)-free N-methyl-D-glucamine (NMG) medium, to avoid the activation of VSCCs indirectly by the glutamate receptor agonists, stimulation of the glutamate receptors causes Ca2+ influx only through NMDA and AMPA/kainate receptor-associated channels, and that Ca2+ entry correlates well with subsequent cell death. These results show that the activation of NMDA or AMPA/kainate receptors can cause excitotoxicity in retinal neurons by mechanisms not involving Na+ influx, but rather depending on the permeation of Ca2+ through glutamate receptor-associated channels. For small Ca2+ loads the entry of Ca2+ through the NMDA receptor-associated channel was more efficient in triggering cell death than the influx of Ca2+ through the AMPA/kainate receptor.
我们研究了谷氨酸、N-甲基-D-天冬氨酸（NMDA）、海人酸或K⁺去极化对培养的鸡视网膜细胞神经毒性的影响，实验条件为我们能够区分通过离子型谷氨酸受体进入的Ca²⁺和电压敏感性Ca²⁺通道（VSCCs）。当神经元在含Na⁺的培养基中受到NMDA、海人酸或谷氨酸刺激时，观察到细胞存活率下降，而K⁺去极化并不影响细胞活力。Mg²⁺离子完全阻止了NMDA受体介导的毒性作用，并且对α-氨基-3-羟基-5-甲基-4-异恶唑丙酸/海人酸（AMPA/海人酸）受体诱导的细胞死亡有微小但显著的保护作用。我们观察到，在无Na⁺的N-甲基-D-葡糖胺（NMG）培养基中，为避免谷氨酸受体激动剂间接激活VSCCs，谷氨酸受体的刺激仅通过NMDA和AMPA/海人酸受体相关通道引起Ca²⁺内流，并且Ca²⁺内流与随后的细胞死亡密切相关。这些结果表明，NMDA或AMPA/海人酸受体的激活可通过不涉及Na⁺内流的机制导致视网膜神经元兴奋毒性，而是取决于Ca²⁺通过谷氨酸受体相关通道的通透。对于少量Ca²⁺负荷，通过NMDA受体相关通道的Ca²⁺内流比通过AMPA/海人酸受体的Ca²⁺内流在触发细胞死亡方面更有效。
