NFAT-induced Regional Variations in Kv4 Channel Expression in Heart

描述(由申请人提供)：电压门控K(Kv)电流在整个左室壁上以不同的方式分布。左室心外膜(EPI)细胞的Kv4电流大于心内膜(Endo)细胞。Kv4通道功能的这种不均匀分布是正常心肌复极所必需的。我们最近报道，通过激活对钙敏感的磷酸酶钙调神经磷酸酶和转录因子NFATc3，[钙]i的变化转化为Kv4表达的变化。这导致我们发现，跨左室游离壁的[钙]i/钙调神经磷酸酶/NFATc3信号的差异是Kv4表达跨壁变化的基础。然而，细胞内钙离子、钙调神经磷酸酶和NFATc3信号的区域差异机制却知之甚少。本申请中提出的工作采用了我们小组开发的一系列新技术和方法来解决这些重要问题。我们的初步数据表明，所提出的实验不仅是可行的，而且将提供关于心脏Kv通道调节的新的基本信息。拟议的工作解决了三个具体的假设。首先，我们将检验这一假说，即在脑室内钙调神经磷酸酶活动的异质性是由[Ca~(2+)]j的区域差异引起的。其次，我们将检验局部和整体[钙]i信号调节NFAT转位和心肌细胞基因表达的假设。然后我们将使用这些数据来确定Endo和EPI细胞之间的[Ca~(2+)]j信号的差异如何导致NFAT活性的地区差异。最后，我们将验证这一假设，即钙调神经磷酸酶/NFATc3信号对于维持脑室Kv电流的异质性是必不可少的。综上所述，这项工作将提供第一个关于心脏中钙信号、兴奋性和收缩能力的综合观点，并显著增强我们对调节Kv通道在健康和疾病中功能的基本机制的理解。

DESCRIPTION (provided by applicant): Voltage-gated K+ (Kv) currents are differentially distributed across the left ventricular wall. Kv4 currents are larger in left ventricular epicardial (EPI) cells than in endocardial (ENDO) cells. This non-uniform distribution of Kv4 channel function is essential for normal myocardial repolarization. We recently reported that variations in [Ca2+]i are transduced into changes in Kv4 expression through the activation of the Ca2+-sensitive phosphatase calcineurin and the transcription factor NFATc3. This led to our discovery that differential [Ca2+]i/calcineurin/NFATc3 signaling across the left ventricular free wall underlies transmural variations in Kv4 expression. However, the mechanisms underlying regional differences in [Ca2+]j, calcineurin, and NFATc3 signaling are poorly understood. The work proposed in this application employs a series of novel techniques and approaches developed by our group to address these important issues. Our preliminary data suggest that the proposed experiments are not only feasible but will provide new fundamental information regarding Kv channel regulation in the heart. The proposed work addresses three specific hypotheses. First, we will test the hypothesis that regional variations in [Ca2+]j underlie heterogeneous calcineurin activity in the ventricle. Second, we will test the hypothesis that local and global [Ca2+]i signals modulate NFAT translocation and gene expression in ventricular myocytes. We will then use these data to determine how variations in [Ca2+]j signals between ENDO and EPI cells lead to regional differences in NFAT activity. Finally, we will test the hypothesis that calcineurin/NFATc3 signaling is essential for maintaining Kv current heterogeneity in the ventricle. Taken together, this work will provide the first integrated view of calcium signaling, excitability, and contractility in the heart and significantly enhance our understanding of the basic mechanisms, which regulate Kv channel function in health and disease.