Manzoni O, Prezeau L, Rassendren F A, Sladeczek F, Curry K, Bockaert J
Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France.
Mol Pharmacol. 1992 Aug;42(2):322-7.
We tested the effects of two enantiomers of a glutamate analogue, (trans)-1-aminocyclopentyl-1,3-dicarboxylate (t-ACPD), in striatal and cerebellar neurons in primary culture, as well as in Xenopus oocytes injected with cerebellar rat RNA. In the presence of MK-801, to avoid N-methyl-D-aspartate receptor activation, and 3 microM tetrodotoxin, both enantiomers [(1R,3S)- and (1S,3R)-t-ACPD] stimulated inositol phosphate (InsP) formation both in striatal neurons after 9-11 days in vitro [EC50, 3.7 +/- 1.1 microM, three experiments, and 33 +/- 7.5 microM, three experiments; maximal stimulatory effects, 252 +/- 15%, 13 experiments, and 269 +/- 15% of basal InsP formation, 14 experiments, for (1R,3S)- and (1S,3R)-t-ACPD, respectively] and in cerebellar granule cells after 9-11 days in vitro [EC50, 50 +/- 18 microM, four experiments, and 307 +/- 92 microM, four experiments; maximal stimulatory effects, 401 +/- 71%, eight experiments, and 423 +/- 75% of basal InsP formation, eight experiments, for (1R,3S)- and (1S,3R)-t-ACPD, respectively]. These effects were not additive, indicating that both enantiomers acted at the same receptor molecule. When we monitored t-ACPD-induced increases in intracellular Ca2+ concentration ([Ca2+]i) with fura-2 ratio-imaging, we found that both enantiomers could elicit similar increase in [Ca2+]i, in the presence of 1 microM MK-801 and 3 microM tetrodotoxin; these effects were also observed in the absence of external Ca2+. Moreover, in Xenopus oocytes injected with adult rat cerebellar RNA, both drugs elicited oscillatory increases of a Ca(2+)-dependent chloride conductance, with similar efficacy, with (1R,3S)-t-ACPD being the more potent isomer. These data are in contradiction to previous reports showing that, in "immature" cerebellar neurons and adult hippocampal slices, (1S,3R)-t-ACPD was either the only active enantiomer or a full agonist of metabotropic receptors, with (1R,3S)-t-ACPD being ineffective or a partial agonist. However, performing these experiments in immature (2-3 days in vitro) striatal or cerebellar neurons, we found that only (1S,3R)-t-ACPD was active in stimulating [Ca2+]i.
我们测试了谷氨酸类似物（反式）-1-氨基环戊基-1,3-二羧酸（t-ACPD）的两种对映体对原代培养的纹状体和小脑神经元以及注射了大鼠小脑RNA的非洲爪蟾卵母细胞的影响。在存在MK-801以避免N-甲基-D-天冬氨酸受体激活和3 microM河豚毒素的情况下，两种对映体[（1R,3S）-和（1S,3R）-t-ACPD]在体外培养9-11天后均能刺激纹状体神经元中肌醇磷酸（InsP）的形成[EC50，3.7±1.1 microM，三个实验；33±7.5 microM，三个实验；最大刺激作用，分别为基础InsP形成的252±15%，13个实验；和269±15%，14个实验，针对（1R,3S）-和（1S,3R）-t-ACPD]以及体外培养9-11天后的小脑颗粒细胞[EC50，50±18 microM，四个实验；307±92 microM，四个实验；最大刺激作用，分别为基础InsP形成的401±71%，八个实验；和423±75%，八个实验，针对（1R,3S）-和（1S,3R）-t-ACPD]。这些作用并非相加性的，表明两种对映体作用于同一受体分子。当我们用fura-2比率成像监测t-ACPD诱导的细胞内Ca2+浓度（[Ca2+]i）增加时，我们发现在存在1 microM MK-801和3 microM河豚毒素的情况下，两种对映体均可引起[Ca2+]i的类似增加；在无细胞外Ca2+时也观察到这些作用。此外，在注射了成年大鼠小脑RNA的非洲爪蟾卵母细胞中，两种药物均引起Ca(2+)依赖性氯电导的振荡性增加，效力相似，其中（1R,3S）-t-ACPD是更有效的异构体。这些数据与先前的报道相矛盾，先前报道显示，在“未成熟”的小脑神经元和成年海马切片中，（1S,3R）-t-ACPD要么是唯一具有活性的对映体，要么是代谢型受体的完全激动剂，而（1R,3S）-t-ACPD无效或为部分激动剂。然而，在未成熟（体外培养2-3天）的纹状体或小脑神经元中进行这些实验时，我们发现只有（1S,3R）-t-ACPD在刺激[Ca2+]i方面具有活性。
