Severe Motor Impairment in Kv3 Channel-deficient Mice

电压门控钾离子通道（K+）是一大类离子通道，参与了静息膜电位的建立、动作电位波形和持续时间的确定、神经递质释放的调节、节律性放电模式和神经元起搏器活动的调节。一些遗传性人类疾病强调了K+通道的关键重要性，其中一些通道功能失调。两个电压门控K+通道Kv3.1和Kv3.3具有独特的生物物理特性，并在整个神经系统中广泛共表达。当在小鼠中单独敲除时，每个突变只显示微妙的（Kv3.1）或没有明显的（Kv3.3）表型。两个共表达的K+通道的功能冗余可能解释了单突变体缺乏强表型。为了研究这种可能性，产生了kv3.1 /3.3双突变体。虽然kv3.1 /3.3缺陷小鼠过度活跃，但它们表现出严重的共济失调、间歇性震颤样运动、肌阵挛和对乙醇过敏。为了了解不同表型性状的细胞起源和分子基础，我们建议：1)使用比较免疫组织化学和脑切片电生理学方法检查突变大脑中两个K+通道通常共表达区域可能的结构和生理改变；2)利用dna微阵列技术检测影响神经递质系统和其他信号分子的基因表达水平可能发生的变化；3)通过将双突变体杂交给转基因小鼠，尝试有针对性地挽救不同的表型性状（肌阵挛、震颤等），其中Kv3.1或Kv3.3 K+通道的表达是由具有明确表达模式的启动子在不同的神经元亚群中驱动的。这些研究产生的知识将有助于确定Kv3.1和Kv3.3 K+通道的生理作用，并增加我们对某些类型的震颤、肌阵挛和乙醇敏感性的病理生理学的理解，为未来开发筛查程序、诊断工具和高危个体的干预策略提供可能性。

Voltage-gated potassium (K+) channels form a large family of ion channels that are involved in establishing the resting membrane potential, in determining the action potential waveform and duration, in regulating release of neurotransmitter, and in modulating rhythmic firing patterns and pacemaker activity of neurons. The pivotal importance of K+ channels is underlined by several inherited human disorders in which some of these channels are dysfunctional. The two voltage-gated K+ channels Kv3.1 and Kv3.3 have unique biophysical properties and are extensively co-expressed throughout the nervous system. When individually knocked out in mice, each mutant displays only a subtle (Kv3.1) or no overt (Kv3.3) phenotype. Functional redundancy of the two co-expressed K+ channels may explain the lack of strong phenotypes in the single mutants. To investigate this possibility Kv3.1/3.3-double mutants were generated. Although Kv3.1/3.3-deficient mice are hyperactive, they display severe ataxia, intermittent tremor-like movements, myoclonus and hypersensitivity to ethanol. To understand the cellular origin and molecular basis of the different phenotypic traits, we propose to 1) examine mutant brains for possible structural and physiological alterations in areas where the two K+ channels are normally co-expressed using comparative immunohistochemistry and brain slice electrophysiology; 2) use the cDNA-microarray technology to detect possible alterations in expression levels of genes influencing neurotransmitter systems and other signaling molecules; and 3) attempt targeted rescue of distinct phenotypic traits (myoclonus, tremor, etc.) by crossing the double mutant to transgenic mice in which expression of Kv3.1 or Kv3.3 K+ channels is driven in distinct neuronal subpopulations by promoters with defined expression patterns. Knowledge generated by these studies will help define the physiological roles of Kv3.1 and Kv3.3 K+ channels and increase our understanding of the pathophysiology of some types of tremor, myoclonus and ethanol sensitivity, offering the possibility of future development of screening procedures, diagnostic tools and intervention strategies for individuals at risk.