Abstract 15961: Syncytial Model of Type 2 Long QT Syndrome Derived From Human iPS Cells Can Be Paced and Responds to Ikr Block and Activation
Type 2 long QT (LQT2) syndrome is a cardiac disorder associated with hERG channel mutation that may lead to tachyarrhythmia and sudden death. We developed a syncytial model of cardiomyocytes (CMs) differentiated from iPS cells derived from an LQT2 patient harboring an A422T mutation. The A422T mutation has been shown to cause a marked decrease in IKr current mainly due to a trafficking defect in the hERG channel. Immunostaining of cTnI revealed that CMs were isotropically distributed with well-formed sarcomeres. Both wild type (WT) and LQT2 monolayers were stable in culture for at least 60 days with spontaneous activity, and could be paced at cycle lengths (CL) from 2000 down to 300 ms. After staining the monolayers with di-4-ANEPPS, optical mapping showed that all monolayers formed a functional syncytium that supported propagating action potentials. LQT2 monolayers had longer APD80s than WT monolayers (332±43 ms, n=6, vs. 267±46 ms, n=18, mean±SD, CL = 700 ms, p<0.005), showing the delayed repolarization expected of the LQT2 phenotype. Reentrant spiral waves were observed in LQT2 (n=2), but not WT monolayers.
Application of 0.2μM E-4031 (IKr blocker) slowed repolarization and prolonged APD80 in both WT and LQT2 monolayers, and slowed conduction velocity in WT monolayers (4.7±1.0 cm/s, n=6 vs. 10.4±1.4 cm/s, n=11 control, CL = 1000 ms). The slowing effect may reflect a role of IKr in setting the maximum diastolic potential in these CMs where IK1 is weakly expressed, as has been recently suggested. Application of 10μM ML-T531 (IKr activator) shortened APD80 in LQT2 monolayers (313±36 ms vs. 162±19 ms, n=4, p<0.0001), showing successful reversal of the LQT phenotype. ML-T531 also shortened APD80 in WT monolayers (202±43 ms vs. 154±26 ms, n=4, p<0.04). These results indicate that syncytial models of heritable cardiac disease are feasible and may be useful for studying drug effects that affect electrophysiology and arrhythmogenesis.
Author Disclosures: R. Zhu: None. R. Joshi-Mukherjee: None. A. Blazeski: None. K.R. Boheler: None. G.F. Tomaselli: None. L. Tung: None.
- © 2014 by American Heart Association, Inc.