Trafficking and Regulation of Cardiovascular K+ Channels

描述（由申请人提供）：本提案的长期目标是了解调节细胞表面水平，心血管离子通道定位和靶向的精确机制。心房颤动是最常见的心律失常，影响着200多万美国人，并导致中风和心力衰竭的严重死亡率。人类心脏的这种电不稳定性可通过继发于结构性心脏病的离子通道重塑引起的后天性疾病或离子通道功能的原发性遗传缺陷而发生。Kv1.5是一个重要的心血管K+通道，对人类心脏心房复极至关重要。功能性Kv1.5细胞表面表达的改变有助于阵发性和持续性心房颤动以及慢性低氧性肺动脉高压的病理生理。值得注意的是，尽管Kv1.5表面表达的变化与心血管疾病之间存在明确的联系，但对其质膜靶向或定位的控制机制知之甚少。最近，我们在肌细胞质膜发现了意想不到的Kv1.5的动态运输，并证明了内在化和再循环在维持稳态离子通道表面水平中的作用。然而，与心脏中的大多数蛋白质相似，心房肌细胞中控制Kv1.5表面水平的分子机制和调控机制尚不清楚。我们假设，在心房肌细胞中，Kv1.5的表面水平是由肌动蛋白和肌动蛋白马达的协调运动控制的，这些马达与Rab GTPases结合在一起，起到调节通道内化和再循环的作用。此外，我们提出这一过程可通过胆碱能刺激调节，并可通过抗心律失常药物结合进行治疗控制。因此，在Specific Aim 1中，我们将明确小鼠和人类心房肌细胞中参与Kv1.5内化和再循环的分子机制。在具体目标2中，我们将确定胆碱能和肾上腺素能刺激对Kv1.5内化和再循环的直接调节的贡献和机制。在Specific Aim 3中，我们将确定抗心律失常药物诱导的Kv1.5通道内化的机制。我们所提出的研究的成功完成无疑将有助于我们了解以Kv1.5表面表达改变为特征的病理生理条件的潜在事件，并可能为设计操纵特定离子通道运输途径以治疗心血管通道病变和心脏电兴奋性调节的新治疗策略提供新的见解。

DESCRIPTION (provided by applicant): The long-term goals of this proposal are to understand the precise mechanisms regulating cell- surface level, localization and targeting of cardiovascular ion channels. Atrial fibrillation is the most common cardiac arrhythmia affecting more than 2 million Americans and results in significant mortality due to stroke and heart failure. This electrical instability in the human heart can occur through an acquired disorder attributable to ion channel remodeling secondary to structural heart disease or as a result from a primary genetic defect in ion channel function. Kv1.5 is a prominent cardiovascular K+ channel that is vital for atrial repolarization in the human heart. Alterations in the cell surface expression of functional Kv1.5 contribute to the pathophysiology of paroxysmal and persistent atrial fibrillation as well as chronic hypoxic pulmonary hypertension. Remarkably, despite the clear links between changes in Kv1.5 surface expression and cardiovascular disease, relatively little is known regarding the mechanisms controlling its plasma membrane targeting or localization. Recently, we have discovered an unexpected dynamic trafficking of Kv1.5 at the myocyte plasma membrane and demonstrated a role for internalization and recycling in the maintenance of steady- state ion channel surface levels. Nonetheless, similar to most proteins in the heart, the molecular machinery and the regulatory mechanisms controlling the surface levels of Kv1.5 in atrial myocytes remain unclear. We hypothesize that, in atrial myocytes, Kv1.5 surface levels are controlled by the coordinated movement of kinesin and myosin motors coupled to the channel by Rab GTPases that act to regulate channel internalization and recycling. Moreover, we propose that this process is modulated by cholinergic stimulation and can be therapeutically controlled by antiarrhythmic drug binding. Therefore in Specific Aim 1, we will define the molecular machinery involved in internalization and recycling of Kv1.5 in mouse and human atrial myocytes. In Specific Aim 2, we will determine the contribution and mechanisms of cholinergic and adrenergic stimulation to the direct modulation of Kv1.5 internalization and recycling. In Specific Aim 3, we will determine the mechanisms of antiarrhythmic drug-induced Kv1.5 channel internalization. Successful completion of our proposed studies will undoubtedly contribute to our knowledge of the events underlying the pathophysiological conditions characterized by altered Kv1.5 surface expression and likely provide novel insight into novel therapeutic strategies designed to manipulate specific ion channel trafficking pathways for the treatment of cardiovascular channelopathies and modulation of cardiac electrical excitability. PUBLIC HEALTH RELEVANCE: Atrial fibrillation (AF) is a common heart-rhythm disturbance affecting millions of Americans with potentially life threatening consequences. Cells in the heart have tiny pores (channels), which allow ions (such as K+, Na+, Ca2+) to cross the cell membrane to conduct the electrical properties of the heart tissue. An important, yet poorly understood property of ion channels is their number and location in the heart cell membrane. Changes in the number of channels or their location can occur in atrial fibrillation. This grant application focuses on understanding the mechanisms that control the cell surface number of certain types of K+ channels that are important for cardiac function in the atria and from which new treatment strategies for AF may be designed.