Bowser David N, Wagner David A, Czajkowski Cynthia, Cromer Brett A, Parker Michael W, Wallace Robyn H, Harkin Louise A, Mulley John C, Marini Carla, Berkovic Samuel F, Williams David A, Jones Mathew V, Petrou Steven
Department of Physiology, University of Melbourne, Victoria 3010, Australia.
Proc Natl Acad Sci U S A. 2002 Nov 12;99(23):15170-5. doi: 10.1073/pnas.212320199. Epub 2002 Nov 1.
The gamma-aminobutyric acid type A (GABA(A)) receptor mediates fast inhibitory synaptic transmission in the CNS. Dysfunction of the GABA(A) receptor would be expected to cause neuronal hyperexcitability, a phenomenon linked with epileptogenesis. We have investigated the functional consequences of an arginine-to-glutamine mutation at position 43 within the GABA(A) gamma(2)-subunit found in a family with childhood absence epilepsy and febrile seizures. Rapid-application experiments performed on receptors expressed in HEK-293 cells demonstrated that the mutation slows GABA(A) receptor deactivation and increases the rate of desensitization, resulting in an accumulation of desensitized receptors during repeated, short applications. In Xenopus laevis oocytes, two-electrode voltage-clamp analysis of steady-state currents obtained from alpha(1)beta(2)gamma(2) or alpha(1)beta(2)gamma(2)(R43Q) receptors did not reveal any differences in GABA sensitivity. However, differences in the benzodiazepine pharmacology of mutant receptors were apparent. Mutant receptors expressed in oocytes displayed reduced sensitivity to diazepam and flunitrazepam but not the imidazopyridine zolpidem. These results provide evidence of impaired GABA(A) receptor function that could decrease the efficacy of transmission at inhibitory synapses, possibly generating a hyperexcitable neuronal state in thalamocortical networks of epileptic patients possessing the mutant subunit.
γ-氨基丁酸A型（GABA(A)）受体介导中枢神经系统中的快速抑制性突触传递。预计GABA(A)受体功能障碍会导致神经元过度兴奋，这是一种与癫痫发生相关的现象。我们研究了在一个患有儿童失神癫痫和热性惊厥的家族中发现的GABA(A)γ(2)亚基第43位精氨酸突变为谷氨酰胺的功能后果。对在HEK-293细胞中表达的受体进行的快速应用实验表明，该突变减缓了GABA(A)受体的失活并增加了脱敏速率，导致在重复的短时间应用过程中脱敏受体的积累。在非洲爪蟾卵母细胞中，对从α(1)β(2)γ(2)或α(1)β(2)γ(2)(R43Q)受体获得 的稳态电流进行的双电极电压钳分析未发现GABA敏感性有任何差异。然而，突变受体的苯二氮䓬药理学差异很明显。在卵母细胞中表达的突变受体对地西泮和氟硝西泮的敏感性降低，但对咪唑吡啶唑吡坦不敏感。这些结果提供了GABA(A)受体功能受损的证据，这可能会降低抑制性突触处的传递效率，并可能在拥有突变亚基的癫痫患者的丘脑皮质网络中产生过度兴奋的神经元状态。
