The voltage dependence of recovery from use-dependent block by QX-222 separates mechanisms for drug egress in the cardiac sodium channel.
The voltage dependence of recovery from use-dependent block by QX-222 separates mechanisms for drug egress in the cardiac sodium channel.
复制标题
QX-222 从使用依赖性阻断中恢复的电压依赖性分离了心脏钠通道中药物流出的机制。
DOI：
10.1016/j.bcp.2006.01.010
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发表时间：
2006
影响因子：
5.8
通讯作者：
Lee,PeterJ
中科院分区：
文献类型：
--
作者：
Lardin,HarveyA;Lee,PeterJ
在鱿鱼巨大轴突的神经元钠通道中，QX-222阻滞剂的恢复因超极化而减慢。然而，在心室细胞中，超极化可以加速恢复。此前，我们发现心脏钠通道异构体(D1P-loop C373和D4S6 T1752)外侧的异构体特异性残基影响利多卡因的使用依赖性阻断(UDB)。为了确定这些同型残基是否有助于在心室肌细胞中观察到的对比电压依赖的恢复，我们测量了QX-222在保持电位120、140、160和180 mV时对野生型心脏通道(WT)、突变体C373Y(CY)和T1752V(TV)以及C373Y/T1752V(CY/TV)的UDB的恢复率。与神经元通道不同，在超极化电位下，心脏钠通道从Qx阻断中恢复得更快。所有突变都减缓了QX-222的恢复，其中双重突变体的降幅最大，表明异构体特定残基定义了外部药物路径。在测试范围内，回收率与电压呈线性关系，我们使用速率-电压曲线的斜率来量化电压依赖关系。TV突变在没有改变斜率的情况下导致恢复率下降，表明突变关闭了一条电压无关的出口路径。然而，CY突变使斜率变平，降低了恢复的电压依赖性。此外，CY/TV引起的降幅小于CY和TV的降幅之和，说明这两种残留物的影响是相互关联的。因此，我们认为C373和T1752通过不同的机制改变了UDB的回收率，但决定了共同的药物出口路径。
In neuronal sodium channels of squid giant axons, recovery from QX-222 block is slowed by hyperpolarization. However, in ventricular cells, hyperpolarization speeds recovery. Previously, we showed that isoform-specific residues in the external side of the cardiac sodium channel isoform (D1P-loop C373 and D4S6 T1752) influence use-dependent block (UDB) by lidocaine. To determine whether these isoformspecific residues contribute to the contrasting voltage-dependent recovery observed in ventricular myocytes, we measured recovery rates from UDB by QX-222 at holding potentials of 120, 140, 160 and 180mV for wild-type cardiac channel (WT), the mutants C373Y (CY) and T1752V (TV), and C373Y/T1752V (CY/TV). Unlike neuronal channels, cardiac sodium channels recovered from QX block faster at hyperpolarized potentials. All mutations slowed QX-222 recovery, with the greatest rate reduction observed for the double mutant, indicating that the isoform-specific residues define external drug paths. The recovery rates varied linearly with voltage over the range tested, and we used the slopes of rate versus voltage plots to quantify voltage dependence. The TV mutation caused reduction in recovery rates without changing the slope, indicating that the mutation closed a voltage-independent egress path. The CY mutation, however, flattened the slope and reduced the voltage dependence of recovery. In addition, the reduction in rate caused by CY/TV is less than the sum of those for CY and TV, suggesting that the impacts of these two residues are interrelated. Therefore, we propose that the isoform-specific residues C373 and T1752 change recovery from UDB by distinct mechanisms but determine a common drug egress path.