Beltrán González Andrea N, Vicentini Florencia, Calvo Daniel J
Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenos Aires, Argentina.
J Neurochem. 2018 Jan;144(1):50-57. doi: 10.1111/jnc.14237. Epub 2017 Nov 7.
l-Cysteine is an endogenous sulfur-containing amino acid with multiple and varied roles in the central nervous system, including neuroprotection and the maintenance of the redox balance. However, it was also suggested as an excitotoxic agent implicated in the pathogenesis of neurological disorders such as Parkinson's and Alzheimer's disease. l-Cysteine can modulate the activity of ionic channels, including voltage-gated calcium channels and glutamatergic NMDA receptors, whereas its effects on GABAergic neurotransmission had not been studied before. In the present work, we analyzed the effects of l-cysteine on responses mediated by homomeric GABA ρ1 receptors, which are known for mediating tonic γ-aminobutyric acid (GABA) responses in retinal neurons. GABA ρ1 receptors were expressed in Xenopus laevis oocytes and GABA-evoked chloride currents recorded by two-electrode voltage-clamp in the presence or absence of l-cysteine. l-Cysteine antagonized GABA ρ1 receptor-mediated responses; inhibition was dose-dependent, reversible, voltage independent, and susceptible to GABA concentration. Concentration-response curves for GABA were shifted to the right in the presence of l-cysteine without a substantial change in the maximal response. l-Cysteine inhibition was insensitive to chemical protection of the sulfhydryl groups of the ρ1 subunits by the irreversible alkylating agent N-ethyl maleimide. Our results suggest that redox modulation is not involved during l-cysteine actions and that l-cysteine might be acting as a competitive antagonist of the GABA ρ1 receptors.
L-半胱氨酸是一种内源性含硫氨基酸，在中枢神经系统中具有多种不同作用，包括神经保护和维持氧化还原平衡。然而，它也被认为是一种兴奋性毒性剂，与帕金森病和阿尔茨海默病等神经疾病的发病机制有关。L-半胱氨酸可以调节离子通道的活性，包括电压门控钙通道和谷氨酸能N-甲基-D-天冬氨酸（NMDA）受体，而其对γ-氨基丁酸（GABA）能神经传递的影响此前尚未得到研究。在本研究中，我们分析了L-半胱氨酸对同聚GABA ρ1受体介导的反应的影响，该受体以介导视网膜神经元中的紧张性GABA反应而闻名。GABA ρ1受体在非洲爪蟾卵母细胞中表达，并在存在或不存在L-半胱氨酸的情况下通过双电极电压钳记录GABA诱发的氯离子电流。L-半胱氨酸拮抗GABA ρ1受体介导的反应；抑制作用呈剂量依赖性、可逆、电压非依赖性且对GABA浓度敏感。在存在L-半胱氨酸的情况下，GABA的浓度-反应曲线向右移动，最大反应无实质性变化。L-半胱氨酸抑制对不可逆烷基化剂N-乙基马来酰亚胺对ρ1亚基巯基的化学保护不敏感。我们的结果表明，L-半胱氨酸作用过程中不涉及氧化还原调节，并且L-半胱氨酸可能作为GABA ρ1受体的竞争性拮抗剂起作用。
