Simard Chantale, Drolet Benoit, Yang Ping, Kim Richard B, Roden Dan M
Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University of Medicine, 532 Medical Research Bldg I, Nashville, TN 37232, USA.
Clin Pharmacol Ther. 2005 Mar;77(3):138-44. doi: 10.1016/j.clpt.2004.10.008.
Common deoxyribonucleic acid polymorphisms that modulate normal cardiac electrophysiologic characteristics have previously been identified in long QT syndrome disease genes. In this study we screened an additional gene encoding the cardiac potassium channel KCNA5 (underlying I(Kur)) in 3 ethnic groups and evaluated the functional consequences of the variants identified.
The coding region was screened by single-stranded conformational polymorphism analysis and direct sequencing, and nonsynonymous variants were studied by patch-clamping transfected Chinese hamster ovary cells. Results Five synonymous and 6 nonsynonymous polymorphisms were found in KCNA5. None of these polymorphisms was present in greater than 7% of alleles screened or in all 3 ethnic groups. Expression of the nonsynonymous KCNA5 variants revealed normal gating. However, 2 variants (P532L and R578K, both in the C-terminus) were resistant to block by the prototypical inhibitor quinidine; the concentration required to block I(Kur) by 50% (IC(50)) was 8.4 micromol/L for wild type versus 54 micromol/L for R578K and 133 micromol/L for P532L (both P < .0001, versus wild type).
KCNA5 displays little variability in its coding region. C-terminal KCNA5 variants displayed near-normal gating but striking resistance to drug block; thus these pharmacogenomic studies have identified a heretofore-unappreciated role of this region as a modulator of channel sensitivity to drugs. Resistance to I(Kur) blockers may be genetically determined.
先前已在长QT综合征疾病基因中鉴定出调节正常心脏电生理特征的常见脱氧核糖核酸多态性。在本研究中，我们在3个种族群体中筛选了另一个编码心脏钾通道KCNA5（I(Kur)的基础）的基因，并评估了所鉴定变体的功能后果。
通过单链构象多态性分析和直接测序筛选编码区，通过膜片钳技术研究转染的中国仓鼠卵巢细胞中的非同义变体。结果在KCNA5中发现了5个同义多态性和6个非同义多态性。这些多态性在筛选的等位基因中均未超过7%，也未在所有3个种族群体中出现。非同义KCNA5变体的表达显示门控正常。然而，2个变体（均在C末端的P532L和R578K）对原型抑制剂奎尼丁的阻断具有抗性；野生型阻断I(Kur)50%所需的浓度（IC(50)）为8.4 μmol/L，而R578K为54 μmol/L，P532L为133 μmol/L（两者与野生型相比，P <.0001）。
KCNA5在其编码区显示出很少的变异性。C末端KCNA5变体显示出接近正常的门控，但对药物阻断具有显著抗性；因此，这些药物基因组学研究确定了该区域作为通道对药物敏感性调节剂的前所未有的作用。对I(Kur)阻滞剂的抗性可能是由基因决定的。
