de Mello F G
Brain Res. 1984 May;316(1):7-13. doi: 10.1016/0165-3806(84)90003-8.
Glutamate decarboxylase (L-glutamate 1-carboxylase, (EC 4.1.1.15) activity increased 7-fold during the course of differentiation of retina cell aggregate cultures prepared from 8-day-old embryos. The addition of 5 mM GABA in the culture medium almost completely prevented the appearance of GAD activity normally observed during the differentiation of the aggregates. This effect was readily reversible after shifting the aggregates to a GABA-free medium. Differentiated cultures, characterized by high GAD specific activity were also sensitive to GABA treatment, which promoted 50% decrease in the enzyme activity after 7 h incubation of the aggregates in the presence of 0.01 mM GABA. Maximal inhibition was obtained at 0.1 mM GABA. However, GABA up to 10 mM concentration had no effect on GAD activity when added directly to homogenates of retinal tissue. The GABA-mediated inhibition of GAD was antagonized by picrotoxin. The ED50 for picrotoxin to revert GAD inhibition by 0.01 mM GABA was approximately 2 microM. The time course for the decay in GAD activity of cultures exposed to 5 mM GABA, revealed two first-order kinetic components. For an 8-day-old culture the first component had a T1/2 of approximately 60 min and the second decayed with a T1/2 of approximately 315 min. In 13-day-old cultures the first component of GAD decay was identical to the one observed in 8-day-old cultures. The second component, however, was insensitive to GABA inhibition.
谷氨酸脱羧酶（L-谷氨酸1-羧化酶，（EC 4.1.1.15））活性在由8日龄胚胎制备的视网膜细胞聚集体培养物分化过程中增加了7倍。在培养基中添加5 mM GABA几乎完全阻止了聚集体分化过程中正常观察到的GAD活性的出现。将聚集体转移到无GABA的培养基后，这种作用很容易逆转。以高GAD比活性为特征的分化培养物对GABA处理也敏感，在0.01 mM GABA存在下将聚集体孵育7小时后，GABA促进酶活性降低50%。在0.1 mM GABA时获得最大抑制作用。然而，当直接添加到视网膜组织匀浆中时，高达10 mM浓度的GABA对GAD活性没有影响。GABA介导的GAD抑制作用被印防己毒素拮抗。印防己毒素逆转0.01 mM GABA对GAD抑制作用的ED50约为2 microM。暴露于5 mM GABA的培养物中GAD活性衰减的时间进程显示出两个一级动力学成分。对于8日龄培养物，第一个成分的T1/2约为60分钟，第二个成分以约315分钟的T1/2衰减。在13日龄培养物中，GAD衰减的第一个成分与在8日龄培养物中观察到的相同。然而，第二个成分对GABA抑制不敏感。
