Function and Modulation of Somatic and Dendritic Kv3.3 Channels in Purkinje Cells

描述（由申请人提供）：离子通道的点突变如何导致运动缺陷、智力迟钝和大量神经变性？最近发现钾通道Kv3.3的突变是导致人类脊髓小脑共济失调SCA13的原因。患有Kv3.3突变的患者显示小脑萎缩，并出现严重的神经肌肉和认知症状。这项研究的重点是小脑浦肯野细胞中Kv3.3通道的功能，并且有助于理解SCA13人类疾病的病理生理学。Kv3.3在浦肯野细胞中表达最强，蛋白质定位于胞体、轴突和树突中。浦肯野细胞的一个高度定型的反应是复杂的尖峰，一个大规模的全或无反应攀登纤维激活涉及体细胞和树突状细胞的电活动和大的树突状Ca ++瞬变。由于Kv3.3亚基的表达和电特性，我们推测它们在复杂锋电位中是活跃的，并且在调节树突状细胞Ca++内流中是重要的。我们打算使用药理学和遗传学的方法来阐明体细胞和树突状Kv3.3通道在调节浦肯野细胞的电特性和Ca++动力学的具体功能。改变的Ca++稳态是Kv3.3突变人类病理学的可能原因，这些研究对于确定这些通道在调节Ca++动力学中的作用至关重要。本实验室的研究表明，在异源表达系统中，PKC对Kv3.3亚基具有调节作用。PKC在浦肯野细胞的功能和可塑性中起重要作用，Kv3.3的这种调节可能是PKC细胞效应的重要机制。此外，PKC γ的突变是人类脊髓小脑共济失调SCA14的原因。因此，Kv3.3或PKC γ的突变产生相似的表型，提出了一种有趣的可能性，即Kv3.3通道的调节参与了PKC γ突变的人类疾病的表达。本研究的第二个目的是证明浦肯野细胞中的调制和Kv3.3亚基，并开始探索这种调制对浦肯野细胞生理学的影响。

DESCRIPTION (provided by applicant): How can a point mutation in an ion channel cause motor deficits, mental retardation and massive neurodegeneration? It was recently discovered that mutations in potassium channel Kv3.3 is the cause of human spinocerebellar ataxia SCA13. Affected individuals with mutations in Kv3.3 display cerebellar atrophy and present with severe neuromuscular and cognitive symptoms. This research focuses on the function of Kv3.3 channels in Purkinje cells of the cerebellum, and is a contribution in understanding the pathophysiology of disease in humans with SCA13. Kv3.3 is most strongly expressed in Purkinje cells, with protein localization in somas, axons and dendrites. A highly stereotyped response of Purkinje cells is the complex spike, a massive all-or-none response to climbing fiber activation involving somatic and dendritic electrical activity and large dendritic Ca ++ transients. Due to the expression and electrical properties of Kv3.3 subunits, we hypothesize that they are active in the complex spike and important in the regulation dendritic Ca++ influx. We intend to use pharmacological and genetic approaches to elucidate the specific functions of somatic and dendritic Kv3.3 channels in modulating the electrical properties and Ca++ dynamics of Purkinje cells. Altered Ca++ homeostasis is a probable cause of pathology in humans with Kv3.3 mutations, and these studies are critical in establishing the roles of these channels in regulating Ca++ dynamics. Studies in our laboratory demonstrated the modulation of Kv3.3 subunits by PKC in heterologous expression systems. PKC plays very important roles in Purkinje cell function and plasticity, and it is possible that this modulation of Kv3.3 is an important mechanism in the cellular effects of PKC. Moreover, mutations in PKC gamma are the cause of human spinocerebellar ataxia SCA14. Thus, mutations in either Kv3.3 or PKC gamma produce similar phenotypes, posing the intriguing possibility that modulation of Kv3.3 channels is involved in the expression of disease in humans with mutations in PKC gamma. A second aim of this study is to demonstrate the modulation and Kv3.3 subunits in Purkinje cells and begin to explore the implications of this modulation on Purkinje cell physiology.