Flecainide sensitivity of a Na channel long QT mutation shows an open-channel blocking mechanism for use-dependent block.
Flecainide sensitivity of a Na channel long QT mutation shows an open-channel blocking mechanism for use-dependent block.
复制标题
Na 通道长 QT 突变的氟卡尼敏感性显示了使用依赖性阻断的开放通道阻断机制。
DOI：
10.1152/ajpheart.01317.2005
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Lee,PeterJ
中科院分区：
文献类型：
--
作者：
Zhu,Yujie;Kyle,JohnW;Lee,PeterJ
心脏钠通道中的长QT突变D1790 G（DG）显示氟卡尼使用依赖性阻滞（UDB）增强。氟卡尼UDB中通道开放和失活状态的相对重要性一直存在争议。我们使用了一种可修饰的失活缺陷突变通道，该通道在IFM基序中含有F1486 C突变，以研究野生型（WT-ICM）和DG（DG-ICM）通道之间的UDB差异。DG-ICM中5 Hz时的UDB大于WT-ICM，稳态UDB的IC 50值分别为7.19和18.06 μM。当移液器中含有[2-（三甲基铵）乙基]甲硫基磺酸溴盐（MTSET）并禁用快速灭活时，DG-ICM和WT-ICM的IC 50分别为5.04 μM和12.63 μM。我们直接在MTSET处理的非失活ICM通道中测量氟卡尼的开放通道阻滞。DG-ICM的稳态阻滞高于WT-ICM（DG-ICM的IC 50为2.34 μM，WT-ICM为5.87 μM），表明开放通道阻滞是氟卡尼UDB的重要决定因素。我们得到的协会（kon）和解离（koff）率开放通道阻滞的Langmuir等温模型。对WT-ICM，koff = 31.37 s-1，kon= 5.83 s-1·μM-1，计算出的Kd = 5.38 μM（其中Kd =koff/kon）;对DG-ICM，koff = 24.88 s-1，kon= 9.54 s-1·μM-1，计算出的Kd = 2.61 μM。这些Kd值与稳态开放通道阻滞测定的IC_（50）相似。此外，我们通过使用这些动力学速率对UDB进行数学建模，发现该模型准确地预测了实验UDB。从城市开发银行回收的款项对城市开发银行的贡献很小。氟卡尼UDB主要由开放通道阻断机制决定，DG-ICM通道似乎具有改变的开放通道状态，氟卡尼亲和力高于WT-ICM。
A long QT mutation in the cardiac sodium channel, D1790G (DG), shows enhanced flecainide use-dependent block (UDB). The relative importance of open and inactivated states of the channel in flecainide UDB has been controversial. We used a modifiable, inactivation-deficient mutant channel that contains the F1486C mutation in the IFM motif to investigate the UDB difference between the wild-type (WT-ICM) and DG (DG-ICM) channels. UDB at 5 Hz was greater in DG-ICM than WT-ICM, and IC50values for steady-state UDB were 7.19 and 18.06 μM, respectively. When [2-(trimethyammonium) ethyl]methanethiosulfonate bromide (MTSET) was included in the pipette and fast inactivation was disabled, IC50was 5.04 μM for DG-ICM and 12.63 μM for WT-ICM. We measured open-channel block by flecainide directly in MTSET-treated, noninactivating ICM channels. Steady-state block was higher for DG-ICM than WT-ICM (IC50was 2.34 μM for DG-ICM and 5.87 μM for WT-ICM), suggesting that open-channel block is an important determinant of flecainide UDB. We obtained association (kon) and dissociation (koff) rates for open-channel block by the Langmuir-isotherm model. They werekoff= 31.37 s−1,kon= 5.83 s−1·μM−1, and calculatedKd= 5.38 μM for WT-ICM (whereKd=koff/kon); andkoff= 24.88 s−1,kon= 9.54 s−1·μM−1, and calculatedKd= 2.61 μM for DG-ICM. TheseKdvalues were similar to IC50measured from steady-state open-channel block. Furthermore, we modeled UDB mathematically by using these kinetic rates and found that the model predicted experimental UDB accurately. The recovery from UDB had a minor contribution to UDB. Flecainide UDB is predominantly determined by an open-channel blocking mechanism, and DG-ICM channels appeared to have an altered open-channel state with higher flecainide affinity than WT-ICM.