{"title":"An unidentified yet notable modification on INa and IK(DR) caused by ramelteon","authors":"Po-Ming Wu, Yi-Fang Tu, Hsin-Yen Cho, Meng-Cheng Yu, Yen-Hsien Wu, Sheng-Nan Wu","doi":"10.1096/fba.2024-00008","DOIUrl":null,"url":null,"abstract":"<p>Despite advancement in anti-seizure medications, 30% of patients continue to experience recurrent seizures. Previous data indicated the antiepileptic properties of melatonin and its agonists in several animal models. However, the underlying mechanisms of melatonin and its agonists on cellular excitability remain poorly understood. In this study, we demonstrated the electrophysiological changes of two main kinds of ion channels that are responsible for hyperexcitability of neurons after introduction of melatonin agonists- ramelteon (RAM). In Neuro-2a cells, the amplitude of voltage-gated Na<sup>+</sup> (<i>I</i><sub>Na</sub>) and delayed-rectifier K<sup>+</sup> currents (<i>I</i><sub>K (DR)</sub>) could be suppressed under RAM. The IC<sub>50</sub> values of 8.7 and 2.9 μM, respectively. RAM also diminished the magnitude of window Na<sup>+</sup> current (<i>I</i><sub>Na (W)</sub>) elicited by short ascending ramp voltage, with unchanged the overall steady-state current–voltage relationship. The decaying time course of <i>I</i><sub>Na</sub> during a train of depolarizing pulses arose upon the exposure to RAM. The conditioning train protocol which blocked <i>I</i><sub>Na</sub> fitted the recovery time course into two exponential processes and increased the fast and slow time constant of recovery the presence of RAM. In pituitary tumor (GH<sub>3</sub>) cells, <i>I</i><sub>Na</sub> amplitude was also effectively suppressed by the RAM. In addition, GH3-cells exposure to RAM decreased the firing frequency of spontaneous action potentials observed under current-clamp conditions. As a result, the RAM-mediated effect on INa was closely associated with its ability to decrease spontaneous action potentials. Collectively, we found the direct attenuation of <i>I</i><sub>Na</sub> and <i>I</i><sub>K (DR)</sub> caused by RAM besides the agonistic action on melatonin receptors, which could partially explain its anti-seizure activity.</p>","PeriodicalId":12093,"journal":{"name":"FASEB bioAdvances","volume":null,"pages":null},"PeriodicalIF":2.5000,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11452446/pdf/","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"FASEB bioAdvances","FirstCategoryId":"1085","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1096/fba.2024-00008","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"BIOCHEMISTRY & MOLECULAR BIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Despite advancement in anti-seizure medications, 30% of patients continue to experience recurrent seizures. Previous data indicated the antiepileptic properties of melatonin and its agonists in several animal models. However, the underlying mechanisms of melatonin and its agonists on cellular excitability remain poorly understood. In this study, we demonstrated the electrophysiological changes of two main kinds of ion channels that are responsible for hyperexcitability of neurons after introduction of melatonin agonists- ramelteon (RAM). In Neuro-2a cells, the amplitude of voltage-gated Na+ (INa) and delayed-rectifier K+ currents (IK (DR)) could be suppressed under RAM. The IC50 values of 8.7 and 2.9 μM, respectively. RAM also diminished the magnitude of window Na+ current (INa (W)) elicited by short ascending ramp voltage, with unchanged the overall steady-state current–voltage relationship. The decaying time course of INa during a train of depolarizing pulses arose upon the exposure to RAM. The conditioning train protocol which blocked INa fitted the recovery time course into two exponential processes and increased the fast and slow time constant of recovery the presence of RAM. In pituitary tumor (GH3) cells, INa amplitude was also effectively suppressed by the RAM. In addition, GH3-cells exposure to RAM decreased the firing frequency of spontaneous action potentials observed under current-clamp conditions. As a result, the RAM-mediated effect on INa was closely associated with its ability to decrease spontaneous action potentials. Collectively, we found the direct attenuation of INa and IK (DR) caused by RAM besides the agonistic action on melatonin receptors, which could partially explain its anti-seizure activity.
尽管抗癫痫药物取得了进步,但仍有 30% 的患者会反复出现癫痫发作。以前的数据表明,褪黑激素及其激动剂在多个动物模型中具有抗癫痫特性。然而,人们对褪黑素及其激动剂影响细胞兴奋性的内在机制仍然知之甚少。在这项研究中,我们证实了两种主要离子通道的电生理变化,它们是导致神经元过度兴奋的原因。在 Neuro-2a 细胞中,电压门控 Na+ 电流(I Na)和延迟整流 K+ 电流(I K (DR))的振幅在 RAM 的作用下受到抑制。IC50 值分别为 8.7 和 2.9 μM。RAM 还能减弱短时间上升斜坡电压引起的窗口 Na+ 电流(I Na (W))的大小,但总体稳态电流-电压关系不变。一连串去极化脉冲期间 I Na 的衰减时间过程是在暴露于 RAM 后出现的。阻断 I Na 的调节训练方案将恢复时间过程拟合为两个指数过程,并增加了 RAM 存在时恢复的快慢时间常数。在垂体瘤(GH3)细胞中,I Na 振幅也受到 RAM 的有效抑制。此外,GH3 细胞暴露于 RAM 会降低电流钳条件下观察到的自发动作电位的发射频率。因此,RAM 介导的对 INa 的影响与其降低自发动作电位的能力密切相关。总之,我们发现除了对褪黑激素受体的激动作用外,RAM 还能直接减弱 I Na 和 I K(DR),这可以部分解释其抗癫痫活性。