Netopilová M, Drsata J, Kubová H, Mares P
Department of Biochemical Sciences, Faculty of Pharmacy, Charles University, Hradec Králové, Prague, Czech Republic.
Epilepsy Res. 1995 Mar;20(3):179-84. doi: 10.1016/0920-1211(94)00068-8.
Glutamate decarboxylase (EC 4.1.1.15, GAD) activity was studied in the brain of 12-day-old and adult rats treated with 3-mercaptopropionic acid (3-MPA), an inhibitor of GAD competitive with glutamate. Control GAD activity in the brains of immature animals (91.8 +/- 18.2 nmol/h/mg of protein) was lower than that of the adult rats (228 +/- 37.5 nmol/h/mg of protein). Brain GAD inhibition in adult rats was 58% at the onset of seizures (9 min on the average after administration of 70 mg 3-MPA/kg). At the same time, 3-MPA-treated young rats exhibited 76% inhibition of GAD despite the fact that at 9 min these animals were not yet having seizures. At the onset of seizures (19 min after 3-MPA on the average) their GAD activity remained at the same level. The difference between the groups was not related to the presence of the coenzyme pyridoxal-5'-phosphate in the enzyme assay. The inhibition of GAD by 3-MPA in vitro in the immature and adult brains was similar (Ki at 5.1 microM and 4.8 microM concentrations of 3-MPA, respectively). Identical values were found for Km of GAD (at 4.5 mM concentration of L-glutamate). Calculations based on the results suggest that 3-MPA enters the immature brain more easily than the brain of the adult animals. While GAD inhibition by 3-MPA is the primary cause of seizures, their onset is influenced by other factors, in which the immature brain differs from the adult one and which may include less sensitivity to GABA decrease due to relative overactivity of the GABA system.
在12日龄和成年大鼠的大脑中研究了谷氨酸脱羧酶（EC 4.1.1.15，GAD）的活性，这些大鼠用3-巯基丙酸（3-MPA）处理，3-MPA是一种与谷氨酸竞争的GAD抑制剂。未成熟动物大脑中的对照GAD活性（91.8±18.2 nmol/h/mg蛋白质）低于成年大鼠（228±37.5 nmol/h/mg蛋白质）。成年大鼠大脑中的GAD抑制在癫痫发作开始时为58%（平均在给予70 mg 3-MPA/kg后9分钟）。同时，3-MPA处理的幼鼠表现出76%的GAD抑制，尽管在9分钟时这些动物尚未出现癫痫发作。在癫痫发作开始时（平均在3-MPA后19分钟），它们的GAD活性保持在同一水平。两组之间的差异与酶测定中辅酶磷酸吡哆醛-5'-磷酸的存在无关。3-MPA在未成熟和成年大脑中体外对GAD的抑制相似（在3-MPA浓度为5.1 microM和4.8 microM时的Ki分别为）。GAD的Km值相同（在L-谷氨酸浓度为4.5 mM时）。根据结果进行的计算表明，3-MPA比成年动物的大脑更容易进入未成熟大脑。虽然3-MPA对GAD的抑制是癫痫发作的主要原因，但其发作受其他因素影响，未成熟大脑与成年大脑在这些因素方面存在差异，这些因素可能包括由于GABA系统相对过度活跃而对GABA减少的敏感性较低。
