Cell Culture:
Chinese hamster ovary (CHO) cells stably expressing hERG (HERG-CHO) were purchased from American Type Culture Collection (ATCC reference PTA-6812, Manassas, VA). Cells were cultured in Hams F12 nutrient mix (ThermoFisher Scientific, Waltham, USA) supplemented with 5% fetal bovine serum (Sigma-Aldrich, Sydney, Australia) at 37°C with 5% CO2. Cells were passaged using TrypLETM Express Enzyme (ThermoFischer Scientific, Waltham, USA).
Human iPSC (hiPSC) lines, obtained from the Stanford Cardiovascular Institute Biobank, were maintained and differentiated as previously described (16). All lines were derived from donors between 15 and 50 years old. Lines 15C1 and 8C1 were from male subjects and line 142 from a female subject. HiPSC were maintained as colonies on Matrigel® matrix (Corning) in mTeSR™ Plus cell culture medium (StemCell technologies) and passaged using ReLeSR™ (StemCell technologies). Differentiation to cardiomycoytes was performed using the STEMdiff™ Cardiomyocyte differentiation and maintenance Kit (StemCell Technologies). Between days 13-18, cardiomyocytes were dissociated by incubation in 0.2 % Collagenase Type I (ThermoFisher) for 45 minutes at 37°C to break up the matrix, then incubated in 0.25% Trypsin with EDTA for 10 minutes at room temperature to break up cell clumps, before filtering through a 40 µm cell strainer to obtain single hiPSC derived cardiomyocytes (hiPSC-CM).