Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, CP 1428, Ciudad Autónoma de Buenos Aires, Argentina.
J Neurosci. 2011 Jun 29;31(26):9672-82. doi: 10.1523/JNEUROSCI.5157-10.2011.
Ionotropic GABA receptors (GABA(A) and GABA(C)) belong to the Cys-loop receptor family of ligand-gated ion channels. GABA(C) receptors are highly expressed in the retina, mainly localized at the axon terminals of bipolar cells. Ascorbic acid, an endogenous redox agent, modulates the function of diverse proteins, and basal levels of ascorbic acid in the retina are very high. However, the effect of ascorbic acid on retinal GABA receptors has not been studied. Here we show that the function of GABA(C) and GABA(A) receptors is regulated by ascorbic acid. Patch-clamp recordings from bipolar cell terminals in goldfish retinal slices revealed that GABA(C) receptor-mediated currents activated by tonic background levels of extracellular GABA, and GABA(C) currents elicited by local GABA puffs, are both significantly enhanced by ascorbic acid. In addition, a significant rundown of GABA puff-evoked currents was observed in the absence of ascorbic acid. GABA-evoked Cl(-) currents mediated by homomeric ρ(1) GABA(C) receptors expressed in Xenopus laevis oocytes were also potentiated by ascorbic acid in a concentration-dependent, stereo-specific, reversible, and voltage-independent manner. Studies involving the chemical modification of sulfhydryl groups showed that the two Cys-loop cysteines and histidine 141, all located in the ρ(1) subunit extracellular domain, each play a key role in the modulation of GABA(C) receptors by ascorbic acid. Additionally, we show that retinal GABA(A) IPSCs and heterologously expressed GABA(A) receptor currents are similarly augmented by ascorbic acid. Our results suggest that ascorbic acid may act as an endogenous agent capable of potentiating GABAergic neurotransmission in the CNS.
离子型 GABA 受体（GABA(A) 和 GABA(C)）属于配体门控离子通道的 Cys 环受体家族。GABA(C) 受体在视网膜中高度表达，主要定位于双极细胞的轴突末梢。抗坏血酸是一种内源性氧化还原剂，可调节多种蛋白质的功能，而视网膜中的抗坏血酸基础水平非常高。然而，抗坏血酸对视网膜 GABA 受体的影响尚未得到研究。本文显示，抗坏血酸可调节 GABA(C) 和 GABA(A) 受体的功能。金鱼视网膜切片中双极细胞末梢的膜片钳记录显示，由背景水平的细胞外 GABA 引起的 GABA(C) 受体介导的电流，以及由局部 GABA 脉冲引起的 GABA(C) 电流，均被抗坏血酸显著增强。此外，在没有抗坏血酸的情况下，观察到 GABA 脉冲诱发电流的显著衰减。在非洲爪蟾卵母细胞中表达的同型 ρ(1)GABA(C) 受体介导的 GABA 诱导 Cl(-) 电流也被抗坏血酸以浓度依赖性、立体特异性、可逆性和电压独立性方式增强。涉及巯基化学修饰的研究表明，两个 Cys 环半胱氨酸和位于 ρ(1)亚基细胞外结构域的组氨酸 141 均在 GABA(C) 受体被抗坏血酸调节中发挥关键作用。此外，我们还表明，视网膜 GABA(A) IPSC 和异源表达的 GABA(A) 受体电流也被抗坏血酸类似地增强。我们的结果表明，抗坏血酸可能作为一种内源性物质，能够增强中枢神经系统中的 GABA 能神经传递。
