MOLECULAR BASIS OF SODIUM CHANNEL INACTIVATION

这项提议的目的是阐明钠的分子基础 通道停用。NA通道是一种完整的蛋白质， 膜可通过支持电压诱导的快速变化而兴奋 对钠离子的渗透性。失活在以下方面起着关键作用 调节钠通道开放的可用性，从而直接 影响神经、骨骼肌和神经细胞的兴奋性和药物结合 心。膜片钳技术允许记录来自 整个细胞或来自单个钠通道。全细胞失活 记录是明显的，因为在保持期间钠电流的衰减 膜去极化。在单声道录制中，停用是 被视为从电流传导构象的离散转变 将通道蛋白转变为持久的非传导构象。这个 失活态转变的动力学和电压依赖性 可以使用基于马尔可夫链的分析方法来显式描述 理论或艾林率理论。跨膜的结构模型 钠通道的拓扑结构导致了关于该功能的假设 通道的几个高度保守的片段。这些假设 现在可以通过技术联盟严格测试 生物物理学和分子生物学。这项提议针对的是推定的 位于脑部内前庭附近的“失活门” 通道，并似乎摆动或滑动到阻止 毛孔。具体目的是：(1)研究Na通道失活的特征。 单通道录音；(2)调查推定的 失活门和钠通道失活；以及(3)评估 钠的整体行为与失活门的关系 频道。灭活将首先在大鼠身上进行表征和比较 骨骼肌细胞和表达功能性钠的非洲爪哇卵母细胞 通道由编码钠通道A亚基的mRNA组成。后来， 定点突变将用于合成突变的钠通道 与改变的初级氨基酸序列在该区域 失活门。建议的突变包括：(1)缺口突变 划分失活门；(2)改变网络的点突变 失活门上的电荷；以及(3)改变 失活门的灵活性。这些突变的通道，表达 在卵母细胞中，提供了一种方法来探索 结构-功能关系。总体而言，拟议的研究承诺 增进我们对基本电生理学和 钠离子通道的结构特性。

The goal of this proposal is to elucidate the molecular basis of Na channel inactivation. Na channels are integral proteins that render membranes excitable by supporting rapid voltage-induced changes in permeability to Na ions. Inactivation plays a critical role in modulating the availability of Na channels to open and therefore directly influences excitability and drug binding in nerve, skeletal muscle and heart. The patch-clamp technique allows recording of Na currents from whole cells or from single Na channels. Inactivation in whole-cell records is evident as the decay of the Na current during maintained membrane depolarization. In single-channel recordings, inactivation is seen as a discrete transition from a current-conducting conformation of the channel protein to a long-lasting nonconducting conformation. The kinetics and voltage-dependence of transitions to the inactivated state can be explicitly described using analytic methods based on Markov chain theory or Eyring rate theory. Structural models of the transmembrane topology of the Na channel have led to hypotheses regarding the function of several highly conserved segments of the channel. These hypotheses can now be rigorously tested through the alliance of techniques in biophysics and molecular biology. This proposal targets the putative "inactivation gate" which resides near the inner vestibule of the Na channel and appears to swing or slide to a position which blocks the pore. Specific aims are: (1) to characterize Na channel inactivation in single-channel recordings; (2) to investigate links between the putative inactivation gate and Na channel inactivation; and (3) to assess the relationship of the inactivation gate to the overall behavior of Na channels. Inactivation will first be characterized and compared in rat skeletal muscle cells and in Xenopus oocytes which express functional Na channels from mRNA encoding the Na channel a subunit. Subsequently, site-directed mutagenesis will be used to synthesize mutant Na channels with altered primary amino acid sequence in the region of the inactivation gate. Proposed mutations include: (1) nick mutations which divide the inactivation gate; (2) point mutations which change the net charge on the inactivation gate; and (3) point mutations which change the flexibility of the inactivation gate. These mutant channels, expressed in oocytes, provide a means to probe specific aspects of structure-function relationships. Overall, the proposed studies promise to enhance our understanding of fundamental electrophysiological and structural properties of the Na channel.