MOLECULAR DETERMINANTS OF DRUG ACCESS TO THE RECEPTOR-SITE FOR ANTIARRHYTHMIC DRUGS IN THE CARDIAC NA+ CHANNEL
MOLECULAR DETERMINANTS OF DRUG ACCESS TO THE RECEPTOR-SITE FOR ANTIARRHYTHMIC DRUGS IN THE CARDIAC NA+ CHANNEL
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DOI：
10.1073/pnas.92.25.11839
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发表时间：
1995-12-05
影响因子：
11.1
通讯作者：
CATTERALL, WA
中科院分区：
文献类型：
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作者：
QU, YS;ROGERS, J;CATTERALL, WA
局部麻醉和抗心律失常药物的临床疗效是由于它们对Na+通道的电压和频率依赖性阻滞。第四系局部麻醉类似物，如QX-314，是永久带电且不含膜的，当从膜的两侧施用时，可以有效地阻断心脏Na+通道，但仅从细胞内侧阻断神经元Na+通道。当大鼠脑rIIA Na+通道α亚基和大鼠心脏rH1 Na+通道α亚基在tsA-201细胞中短暂表达时，QX-314细胞外通路的差异仍然存在。Na+通道α亚基同源结构域（IVS6）跨膜段S6氨基酸残基对局部麻醉药物阻滞有重要影响。尽管IVS6中的5个氨基酸残基在脑rIIA和心脏rH1中不同，但通过位点定向诱变交换这些氨基酸残基表明，仅rH1中的Thr-1755转化为rIIA中的Val就足以降低细胞外QX-314阻断的速度和程度，并减缓药物在使用依赖性阻断后从封闭通道中逃离的速度。河豚毒素还降低了胞外QX-314的阻滞率，减缓了结合的QX-314在rH1中通过胞外途径的逃逸，表明QX-314必须通过孔才能逃逸。无论给药是细胞外还是细胞内，rH1局部麻醉受体位点的phe1762突变都能抑制QX-314与Ala的结合。因此，QX-314结合到含有ph -1762的rH1 Na+通道α亚基的单个位点上，无论它是从细胞膜的细胞外侧还是细胞内侧施用。从孔的细胞外侧进入该位点是由rH1心脏Na+通道中位置1755的氨基酸决定的。
The clinical efficacy of local anesthetic and antiarrhythmic drugs is due to their voltage- and frequency-dependent block of Na+ channels. Quaternary local anesthetic analogs such as QX-314, which are permanently charged and membrane-impermeant, effectively block cardiac Na+ channels when applied from either side of the membrane but block neuronal Na+ channels only from the intracellular side. This difference in extracellular access to QX-314 is retained when rat brain rIIA Na+ channel alpha subunits and rat heart rH1 Na+ channel alpha subunits are expressed transiently in tsA-201 cells. Amino acid residues in transmembrane segment S6 of homologous domain IV (IVS6) of Na+ channel alpha subunits have important effects on block by local anesthetic drugs. Although five amino acid residues in IVS6 differ between brain rIIA and cardiac rH1, exchange of these amino acid residues by site-directed mutagenesis showed that only conversion of Thr-1755 in rH1 to Val as in rIIA was sufficient to reduce the rate and extent of block by extracellular QX-314 and slow the escape of drug from closed channels after use-dependent block. Tetrodotoxin also reduced the rate of block by extracellular QX-314 and slowed escape of bound QX-314 via the extracellular pathway in rH1, indicating that QX-314 must move through the pore to escape. QX-314 binding was inhibited by mutation of Phe-1762 in the local anesthetic receptor site of rH1 to Ala whether the drug was applied extracellularly or intracellularly. Thus, QX-314 binds to a single site in the rH1 Na+ channel alpha subunit that contains Phe-1762, whether it is applied from the extracellular or intracellular side of the membrane. Access to that site from the extracellular side of the pore is determined by the amino acid at position 1755 in the rH1 cardiac Na+ channel.