Robinson M B, Sinor J D, Dowd L A, Kerwin J F
Children's Hospital of Philadelphia, PA 19104.
J Neurochem. 1993 Jan;60(1):167-79. doi: 10.1111/j.1471-4159.1993.tb05835.x.
Some data suggest that the sodium-dependent, high-affinity L-glutamate (Glu) transport sites in forebrain are different from those in cerebellum. In the present study, sodium-dependent transport of L-[3H]Glu was characterized in cerebellum and cortex. In both cerebellar and cortical tissue, activity was enriched in synaptosomes. Approximately 100 excitatory amino acid analogues were tested as potential inhibitors of transport activity. Many of the compounds tested inhibited transport activity by < 65% at 1 mM and were not studied further. One group of compounds exhibited inhibition conforming to theoretical curves with Hill coefficients of 1 and were < 10-fold selective as inhibitors of transport activity. These included three of the putative endogenous substrates for transport: L-Glu, L-aspartate, and L-cysteate. Four of the compounds exhibited inhibition conforming to theoretical curves with Hill coefficients of 1 and were > 10-fold selective as inhibitors. These included beta-N-oxalyl-L-alpha,beta-diaminopropionate, alpha-methyl-DL-glutamate, (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine, and (2S,1'S,2'S,3'S)-2-(2-carboxy-3-methoxymethylcyclopropyl)glycine. Data obtained with a few of the inhibitors were consistent with two sites in one or both of the brain regions. (2S,1'R,2'R)-2-(Carboxycyclopropyl)glycine (L-CCG-II) was identified as the most potent (IC50 = 5.5 microM) and selective (60-100-fold) inhibitor of transport activity in cerebellum. One of the potential endogenous substrates, L-homocysteate, was also a selective inhibitor of cerebellar transport activity. The data for inhibition of transport activity in cortex by both L-CCG-II and L-homocysteate were best fit to two sites. Kainate was equipotent as an inhibitor of transport activity, and in both brain regions the data for inhibition were best fit to two sites. The possibility that there are four subtypes of excitatory amino acid transport is discussed. Altering sodium and potassium levels affects cerebellar and cortical transport activity differently, suggesting that the differences extend to other recognition sites on these transporters.
一些数据表明，前脑中依赖钠的高亲和力L-谷氨酸（Glu）转运位点与小脑中的不同。在本研究中，对小脑和皮质中L-[3H]Glu的钠依赖性转运进行了表征。在小脑和皮质组织中，活性在突触体中富集。测试了大约100种兴奋性氨基酸类似物作为转运活性的潜在抑制剂。许多测试的化合物在1 mM时对转运活性的抑制率<65%，未进一步研究。一组化合物表现出符合理论曲线的抑制作用，希尔系数为1，作为转运活性抑制剂的选择性<10倍。这些包括三种推测的内源性转运底物：L-谷氨酸、L-天冬氨酸和L-半胱氨酸。四种化合物表现出符合理论曲线的抑制作用，希尔系数为1，作为抑制剂的选择性>10倍。这些包括β-N-草酰-L-α，β-二氨基丙酸、α-甲基-DL-谷氨酸、（2S，1'S，2'S）-2-（羧基环丙基）甘氨酸和（2S，1'S，2'S，3'S）-2-（2-羧基-3-甲氧基甲基环丙基）甘氨酸。用一些抑制剂获得的数据与一个或两个脑区中的两个位点一致。（2S，1'R，2'R）-2-（羧基环丙基）甘氨酸（L-CCG-II）被确定为小脑中转运活性最有效（IC50 = 5.5 microM）和选择性最高（60-100倍）的抑制剂。一种潜在的内源性底物L-高半胱氨酸也是小脑转运活性的选择性抑制剂。L-CCG-II和L-高半胱氨酸对皮质转运活性的抑制数据最适合两个位点。 kainate作为转运活性抑制剂的效力相同，在两个脑区中，抑制数据最适合两个位点。讨论了存在四种兴奋性氨基酸转运亚型的可能性。改变钠和钾水平对小脑和皮质转运活性的影响不同，表明这些差异延伸到这些转运体上的其他识别位点。
