Analysis of QT Prolongation Using Cardiac Action Potential Simulation

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  • YAMAGUCHI Takahiro
    Graduate School of Frontier Sciences, The University of Tokyo
  • ARAFUNE Tatsuhiko
    Graduate School of Frontier Sciences, The University of Tokyo
  • SAKUMA Ichiro
    Graduate School of Frontier Sciences, The University of Tokyo
  • OUCHI Katsuhiro
    Division of Biosystems, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University
  • SHIBATA Nitaro
    Div. of Cardiology, Dept. of Medicine, Tokyo Metropolitan Ohkubo Hospital
  • HONJO Haruo
    Research Institute of Environmental Medicine, Nagoya University
  • KAMIYA Kaichiro
    Research Institute of Environmental Medicine, Nagoya University
  • KODAMA Itsuo
    Research Institute of Environmental Medicine, Nagoya University

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Other Title
  • 心筋細胞活動電位シミュレーションを用いたQT延長メカニズムの検討
  • シンキン サイボウ カツドウ デンイ シミュレーション オ モチイタ QT エンチョウ メカニズム ノ ケントウ

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Abstract

In heart failure, QT interval and action potential duration (APD) is prolonged and IKs, a slow component of delayed rectifier potassium current, decreases. We have reported that the KCNE1 gene, coding IKs channel, increases and QT interval is prolonged in patients with heart failure. Since it is known that increasing KCNE1 increases the maximum conductance of the IKs channel, the mechanism of APD prolongation is not explained by the over expression of KCNE1. In this study, we construct a cardiac membrane action potential simulation model based on the experimental data from oocytes expression to investigate the relationship between the increase of KCNE1 and APD. In the experiment of oocyte expression, 1 ng and 5 ng of KCNE1 were co-injected with 5 ng of KCNQ1. Expressed currents were recorded 1-2 days after injection by the double-microelectrode voltage clamp method at 35 degrees centigrade. Maximum IKs conductance and relationships between time constants, maximum activation parameter and membrane potential were obtained from fitting functions describing IKs channel properties in the Luo-Rudy model to experimental results with the Nelder-Mead simplex method. In simulations, APD was prolonged by increasing the co-injected amount of KCNE1. APD at 5 ng KCNE1 was 183 ms, which is 3.4% longer than that at 1 ng KCNE1 (APD=177 ms). This study shows that increasing the KCNE1 expression level makes maximum IKs conductance increase and IKs channel open slowly and IKs conductance decrease according to the APD time scale. Therefore increasing the KCNE1 expression level may prolong APD with this mechanism. This method of constructing a simulation model based on experiments helps to explain the relationship between KCNE1 expression ratio and QT interval prolongation.

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