Determinants of Cardiac Repolarization

人心脏复极K+电流受插入的功能通道特性之和的支配 进入表面膜。这些通道通常在去极化后打开，以恢复负值 静息潜力。这一过程效率的紊乱可能会导致心肌细胞复极延迟。在……里面 在之前的授权期，我们确定了Kv通道KCNH2电流损失的新机制 (HERG)，并确认蛋白质加工(运输)异常是KCNH2- 连锁(LQT2)长QT综合征。在本研究的初步数据应用中，我们现在展示了近 我们已经研究了40个人类LQT2突变的功能，蛋白运输缺陷是常见的。因此， LQT2的K+电流表型丢失以缺陷蛋白运输为主，少数 在门控或渗透过程中表现出原发异常的突变。我们还证明了错误的处理 通道通常可以被“拯救”以起作用，并且存在多种拯救机制(低温， KCNH2阻断药物、thapsigargin和基因内抑制)。然而，这些救援模式是 对于特定的突变具有选择性，从而提供不同的拯救模式。下一个资助期的具体目标 是：1)继续检验LQT2中复极电流损失是由 主要是由于通道蛋白运输的异常，以及大多数缺乏运输的LQT2 如果突变到达细胞表膜，它们就会形成起作用的通道。2)ER保留率 不同的2类LQT2突变通过不同的机制发生。SubAim 2a将确定不同的步骤 WT KCNH2通道蛋白的分泌途径。SubAim 2b将检验LQT2的假设 突变在这条途径上的不同步骤中断了贩运。3)靶向KCNH2通道蛋白 胆固醇和鞘磷脂富集膜促进细胞表面膜和 修改通道的生物物理属性。为了理性地制定新的战略，增加 突变的KCNH2通道在LQT2中的表面表达，调节细胞机制 KCNH2通道蛋白的转运及其膜插入尚需进一步研究。

Repolarizing K+ current in human heart is governed by the sum of properties of function channels inserted into the surface membrane. These channels normally open following depolarization to restore a negative resting potential. Disturbances in the efficiency of this process can lead to delayed myocyte repolarization. In the previous grant period, we identified novel mechanisms for loss of current of the Kv channel KCNH2 (hERG), and identified protein processing (trafficking) abnormalities as an important mechanism in KCNH2- linked (LQT2) long QT syndrome. In preliminary data in this research application, we now show that of nearly 40 human LQT2 mutations we have studied functionally, protein trafficking defects are common. Thus, the loss of K+ current phenotype in LQT2 is dominated by defective protein trafficking, with a small number of mutations showing primary abnormalities in gating or permeation. We also showed that mis-processed channels often can be "rescued" to function and that multiple mechanisms for rescue exist (low temperature, KCNH2 blocking drugs, thapsigargin, and intragenic suppression). These rescue modalities, however, are selective for specific mutations giving different patterns of rescue. The specific aims for the next grant period are: 1) To continue to test the hypothesis that the loss of repolarizing current in LQT2 is caused predominately by abnormalities in protein trafficking of the channels and that most trafficking-deficient LQT2 mutations form channels that are functional if they reach the cell surface membrane. 2) ER retention of different Class 2 LQT2 mutations occurs by distinct mechanisms. SubAim 2a is to identify distinct steps in the secretory pathway for WT KCNH2 channel protein. SubAim 2b is to test the hypothesis that LQT2 mutations disrupt trafficking at distinct steps in this pathway. 3) Targeting KCNH2 channel proteins into cholesterol and sphingolipid enriched membranes facilitates expression at the cell surface membrane and modifies the biophysical properties of channels. In order to rationally develop new strategies that increase surface expression of mutated KCNH2 channels in LQT2, the cellular mechanisms that regulate the trafficking of KCNH2 channel proteins and their membrane insertion need to be explored.