Abstract 10418: Complex Action Potential Regulation in Cardiomyocytes from Induced Pluripotent Stem Cells (iPSC-CMs) Reveals a Novel Arrhythmia Susceptibility Mechanism

Abstract

Background: While the cardiac sodium channel ( SCN5A ) variants S1103Y and R1193Q have been associated with LQT3 and drug-induced arrhythmia, they are too common to be highly arrhythmogenic: S1103Y allele frequency is 8.1% in Africans and R1193Q 6.1% in East Asians. We have previously reported that S1103Y had no effect on QT in a large biobank or on action potential duration (APD) in iPSC-CMs. Here, we identify a mechanism underlying control of normal baseline repolarization with these variants and study whether the mechanism is generalizable. Methods: Late sodium current (I Na-L ), I Kr , and sensitivity to the blockers dofetilide (I Kr ) and GS967 (I Na-L ) were measured in natural or genome-edited iPSC-CMs carrying S1103Y, R1193Q, or R518X, a common KCNQ1 nonsense variant in the Jervell Lange-Nielsen (JLN) syndrome and unaffected family members. Results: Although APD was unaffected by S1103Y, I Na-L was increased 2~16-fold in SY/YY compared to SS cells (p<0.01) and GS967 shortened APDs only in SY/YY but not in SS cells (p<0.001). Further, I Kr was increased in SY/YY ([SY] 1.2 pA/pF, n=17, p<0.001, [YY] 1.2 pA/pF, n=11, p<0.01) compared to SS cells (0.67 pA/pF, n=20) and challenge with dofetilide prolonged APD by 100 msec at much lower concentrations in SY/YY (median 4.1 nM [SY], 4.2 [YY], n=5-11) compared to SS cells (249 nM, n=14, p<0.001); afterdepolarizations were seen more often in SY/YY (8/16) than in SS cells (1/14). R1193Q also displayed no difference in baseline APD but increased I Kr and I Na-L and increased dofetilide sensitivity. In R518X JLN iPSC-CMs, I Ks was absent as expected but I Kr was increased (1.9 pA/pF, n=5), and editing R518X to wild-type increased I Ks (1.3 pA/pF, n=10) and dramatically decreased I Kr (0.2 pA/pF, n=4). Conclusions: S1103Y and R1193Q increase I Na-L but unexpectedly do not affect baseline repolarization. We hypothesize that increased I Kr through as yet undetermined mechanisms maintains normal repolarization but at the cost of increased sensitivity to I Kr block. The findings with R518X suggest this may be a general mechanism. Our data show that preposition to genetically- or drug-mediated arrhythmias is determined by a complex interaction among multiple repolarizing currents that is not fully captured by heterologous expression systems.