Figure 2

Mutant A735V-Na_V1.5 channels reduce the upstroke velocity of APs in hiPSC-CMs. (a) Distribution of cardiomyocyte phenotypes for all hiPSC-CMs (WT + A735V, left), WT hiPSC-CMs (middle) and A735V hiPSC-CMs (right). Cells were classified according to their AP duration as ventricular-like (APD₅₀> 200 ms), atrial-like (APD₅₀: 20-200 ms) or atypical (APD₅₀ <20 ms or no AP). (b,c) Representative traces of spontaneous action potentials from ventricular-like hiPSC-CMs expressing WT (b) or mutant A735V (c) Na_V1.5 channels. (d–g) Electrophysiological properties of spontaneous APs (mean values ± s.e.m.) from WT (n = 16) and A735V hiPSC-CMs (n = 41): Maximum diastolic potential MDP (d), AP duration at 50% repolarization level APD₅₀ (e), AP amplitude (f) and upstroke velocity (g). (h,i) Representative traces of evoked action potentials from ventricular-like hiPSC-CMs expressing WT (h) or mutant A735V (i) Na_V1.5 channels. For such recordings CMs were hyperpolarized to physiological resting potentials (-80 mV) and action potentials were elicited by intracellular application of short depolarizing current pulses (≤3 nA, 1 ms). (j–m) Electrophysiological properties of evoked APs (mean values ± s.e.m.) from WT (n = 21) and A735V hiPSC-CMs (n = 61): Resting membrane potential RMP (j), AP duration at 50% repolarization level APD₅₀ (k), AP amplitude (l) and upstroke velocity (m). Arrows in (b,c,h,i) mark the phase 0 upstroke of action potentials that is significantly decelerated in BrS-mutant A735V-Na_V1.5 hiPSC-CMs.