Carver J M, Mansson P E, Cortes-Burgos L, Shu J, Zhou L M, Howe J R, Giordano T
Symphony Pharmaceuticals, Inc., Department of Molecular Biology, Malvern, PA 19355, USA.
Brain Res. 1996 May 13;720(1-2):69-74. doi: 10.1016/0006-8993(96)00115-1.
Exposure of neurons either for prolonged periods of time or to high concentrations of excitatory amino acids (EAA), such as glutamate, results in neuronal death. Kainate also causes cell toxicity through the glutamate receptors. However, it is unclear whether the kainate receptor itself mediates any of the toxic responses. In the present study, HEK cells expressing the GluR6 +/- KA2 receptor subunit(s) were studied for their susceptibility to toxicity through the kainate receptor by kainate ligands. The natural ligand, glutamate, did not result in toxicity to the recombinant cell lines over that observed with the untransfected HEK cells, whereas kainate produced a 2-3-fold increase in LDH in both the HEK/GluR6 (ANOVA, P = 0.0001) and HEK/GluR6 + KA2 (ANOVA, P = 0.0002) cell lines following treatment with various dosages, but did not affect the HEK cells. Similar 2-3-fold increases in LDH activity were detected in both recombinant cell lines following treatment with 100 nM of SYM2081 ((2S,4R)-4-methylglutamic acid), a dose at which agonistic activity is elicited. The rank order potencies for eliciting toxicity are consistent with the previously reported EC50 values (SYM2081 > kainate > > > glutamate). Surprisingly, the kainate antagonist, NBQX, was the most toxic of the compounds tested although it had an affinity for the kainate receptor similar to glutamate. Treatment with as little as 10 nM elicited a dramatic increase in toxicity (6-10-fold) in the recombinant cell lines. At 1 microM, NBQX was significantly more toxic (Fisher PLSD, P < 0.05) than any of the other compounds tested. Thus, it appears that cell toxicity can be mediated via kainate receptor through two independent mechanisms: activation and blockage of the kainate receptor.
长时间暴露神经元或使其暴露于高浓度的兴奋性氨基酸（EAA），如谷氨酸，会导致神经元死亡。海人酸也通过谷氨酸受体引起细胞毒性。然而，尚不清楚海人酸受体本身是否介导任何毒性反应。在本研究中，通过海人酸配体研究了表达GluR6+/-KA2受体亚基的HEK细胞对通过海人酸受体产生毒性的敏感性。天然配体谷氨酸对重组细胞系未产生比对未转染的HEK细胞更高的毒性，而在用不同剂量处理后，海人酸使HEK/GluR6（方差分析，P=0.0001）和HEK/GluR6+KA2（方差分析，P=0.0002）细胞系中的乳酸脱氢酶（LDH）增加了2至3倍，但对HEK细胞无影响。在用100 nM的SYM2081（(2S,4R)-4-甲基谷氨酸）处理后，两种重组细胞系中均检测到类似的2至3倍的LDH活性增加，该剂量可引发激动活性。引发毒性的效价顺序与先前报道的EC50值一致（SYM2081>海人酸>>>谷氨酸）。令人惊讶的是，海人酸拮抗剂NBQX是所测试化合物中毒性最大的，尽管它对海人酸受体的亲和力与谷氨酸相似。低至10 nM的处理就会使重组细胞系中的毒性急剧增加（6至10倍）。在1μM时，NBQX的毒性比任何其他测试化合物都显著更高（Fisher最小显著差异法，P<0.05）。因此，似乎细胞毒性可通过海人酸受体通过两种独立机制介导：海人酸受体的激活和阻断。
