Lindegger N, Hagen B M, Marks A R, Lederer W J, Kass R S
Department of Pharmacology, Columbia University College of Physicians and Surgeons, 630 West 168th St., New York, NY 10032, USA.
J Mol Cell Cardiol. 2009 Aug;47(2):326-34. doi: 10.1016/j.yjmcc.2009.04.003. Epub 2009 Apr 14.
Long QT syndrome variant 3 (LQT-3) is a channelopathy in which mutations in SCN5A, the gene coding for the primary heart Na(+) channel alpha subunit, disrupt inactivation to elevate the risk of mutation carriers for arrhythmias that are thought to be calcium (Ca(2+))-dependent. Spontaneous arrhythmogenic diastolic activity has been reported in myocytes isolated from mice harboring the well-characterized Delta KPQ LQT-3 mutation but the link to altered Ca(2+) cycling related to mutant Na(+) channel activity has not previously been demonstrated. Here we have investigated the relationship between elevated sarcoplasmic reticulum (SR) Ca(2+) load and induction of spontaneous diastolic inward current (I(TI)) in myocytes expressing Delta KPQ Na(+) channels, and tested the sensitivity of both to the antianginal compound ranolazine. We combined whole-cell patch clamp measurements, imaging of intracellular Ca(2+), and measurement of SR Ca(2+) content using a caffeine dump methodology. We compared the Ca(2+) content of Delta KPQ(+/-) myocytes displaying I(TI) to those without spontaneous diastolic activity and found that I(TI) induction correlates with higher sarcoplasmic reticulum (SR) Ca(2+). Both spontaneous diastolic I(TI) and underlying Ca(2+) waves are inhibited by ranolazine at concentrations that preferentially target I(NaL) during prolonged depolarization. Furthermore, ranolazine I(TI) inhibition is accompanied by a small but significant decrease in SR Ca(2+) content. Our results provide the first direct evidence that induction of diastolic transient inward current (I(TI)) in Delta KPQ(+/-) myocytes occurs under conditions of elevated SR Ca(2+) load.
长QT综合征3型(LQT-3)是一种离子通道病,编码心脏主要钠离子通道α亚基的基因SCN5A发生突变,破坏了失活过程,增加了突变携带者发生被认为依赖钙(Ca(2+))的心律失常的风险。在携带特征明确的Delta KPQ LQT-3突变的小鼠分离的心肌细胞中,已报道有自发性致心律失常舒张期活动,但此前尚未证明其与突变钠离子通道活性改变相关的钙(Ca(2+))循环改变之间的联系。在此,我们研究了表达Delta KPQ钠离子通道的心肌细胞中肌浆网(SR)钙(Ca(2+))负荷升高与自发性舒张期内向电流(I(TI))诱导之间的关系,并测试了两者对抗心绞痛化合物雷诺嗪的敏感性。我们结合了全细胞膜片钳测量、细胞内钙(Ca(2+))成像以及使用咖啡因释放法测量SR钙(Ca(2+))含量。我们比较了显示I(TI)的Delta KPQ(+/-)心肌细胞与无自发性舒张期活动的细胞的钙(Ca(2+))含量,发现I(TI)诱导与较高的肌浆网(SR)钙(Ca(+))相关。在长时间去极化期间优先靶向I(NaL)的浓度下,雷诺嗪可抑制自发性舒张期I(TI)和潜在的钙(Ca(2+))波。此外,雷诺嗪对I(TI)的抑制伴随着SR钙(Ca(2+))含量的小幅但显著下降。我们的结果提供了首个直接证据,表明Delta KPQ(+/-)心肌细胞中舒张期瞬时内向电流(I(TI))的诱导发生在SR钙(Ca(2+))负荷升高的情况下。