Function of TRAAK current in the rat node of Ranvier

TRAAK电流在大鼠Ranvier结中的作用

• 批准号: 389567163
• 负责人: Professor Dr. Jürgen R. Schwarz
• 金额: --
• 依托单位: Institut für Molekulare Neurogenetik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/389567163?language=en
• 关键词: Function; TRAAK; current; rat; node

We propose experiments to prove a new function of mechano-sensitive TRAAK channels in the rat node of Ranvier. In the mammalian node of Ranvier the action potential is brought about by Na+ current activation and inactivation, activation of voltage-dependent K channels does not contribute to repolarization. This is in contrast to the classical ion theory of the action potential where activation of voltage-dependent K current is important for repolarization. In the mammalian node outward current is provided by a relatively large voltage-independent leakage current (Schwarz and Eikhof, 1987; Schwarz et al., 1995). Recently, the human TRAAK channel was crystallized by R. MacKinnon (Brohawn et al., 2012). The MacKinnon lab also found that TRAAK channels are localized almost exclusively in the node of Ranvier, they do not occur elsewhere in the nervous system. In the proposed experiments we want to analyze the function of these newly discovered mechano-sensitive nodal TRAAK channels. An important prerequisite for this analysis is the detection of a TRAAK blocking compound (Su et al., 2016). We have done preliminary experiments in nodes of Ranvier of single myelinated rat nerve fibers by using the Nonner clamp (Nonner 1969). About 30% of the "leakage" current was blocked by the TRAAK channel blocker and the amplitude of the "leakage" current was almost doubled by 10 µM arachidonic acid and 10 mM trichlorethanol. Since these findings are characteristic for TRAAK channels they indicate the presence of TRAAK channels in the node of Ranvier. We have also shown that nodal TRAAK current is activated by stretching the axoplasma by superfusing the node under investigation with a hypotonic solution. In our grant application we propose experiments to test the hypothesis that the mechano-sensitive TRAAK channels are activated by the transient nodal swelling induced by the influx of Na+ and water during the upstroke of the action potential. The proposed function of TRAAK would be that the stretch-activated K+ current would accelerate action potential repolarization. We want to record action potentials before and after application of the TRAAK blocker and we want to carry out action potential clamp experiments with an action potential as potential template to see whether the TRAAK blocker broadens the inward current. Since TRAAK channels are very temperature-sensitive we want to do experiments at physiological temperature. We expect that the TRAAK current component of the leakage current increases considerably. If our hypothesis is correct then we would have discovered a new mechanism to stabilize the generation of the nodal action potential.

我们提出的实验，以证明一个新的功能的机械敏感TRAAK通道在大鼠的朗维尔结。在哺乳动物朗氏结中，动作电位是由Na+电流激活和失活引起的，电压依赖性K通道的激活对复极化没有贡献。这与动作电位的经典离子理论相反，在经典离子理论中，电压依赖性K电流的激活对复极化很重要。在哺乳动物节点中，外向电流由相对大的电压无关的漏电流提供（施瓦茨和Eikhof，1987;施瓦茨等人，1995年）。最近，人TRAAK通道被R. MacKinnon（Brown等人，2012年）。MacKinnon实验室还发现，TRAAK通道几乎完全位于Ranvier结中，它们不会出现在神经系统的其他地方。在拟议的实验中，我们要分析这些新发现的机械敏感节点TRAAK通道的功能。该分析的重要先决条件是检测TRAAK阻断化合物（Su等人，2016年）。我们已经用Nonner夹（Nonner 1969）在单个有髓大鼠神经纤维的Ranvier结中进行了初步实验。约30%的“漏”电流被TRAAK通道阻滞剂阻断，而10 µM花生四烯酸和10 mM三氯乙醇几乎使“漏”电流的振幅增加了一倍。由于这些发现是TRAAK通道的特征，因此它们表明朗维尔结中存在TRAAK通道。我们还表明，节点TRAAK电流被激活的轴浆体通过超灌的节点下调查与低渗溶液拉伸。在我们的资助申请中，我们提出了实验来测试以下假设：机械敏感性TRAAK通道是由动作电位上升期间Na+和水的流入引起的瞬时节点肿胀激活的。TRAAK的功能可能是牵张激活的K+电流加速动作电位复极。我们想在应用TRAAK阻断剂之前和之后记录动作电位，并且我们想以动作电位作为电位模板进行动作电位钳实验，以观察TRAAK阻断剂是否扩大内向电流。由于TRAAK通道对温度非常敏感，我们希望在生理温度下进行实验。我们预计漏电流的TRAAK电流分量会显著增加。如果我们的假设是正确的，那么我们将发现一种新的机制来稳定节点动作电位的产生。