FIG. 2.

hiPSC-CMs demonstrate electrophysiological maturation and increased heterogeneity with extended time in culture. (A) Optical AP amplitudes are shifted toward larger values after day 16 of differentiation. (B) Optical AP V_max is shifted toward larger values after D16 of differentiation. (C) hiPSC-CMs between D37 and D40 of differentiation (late) respond to TTX with an increased interval between APs compared with the corresponding vehicle treatment. Cells between D16 and D20 of differentiation (early) also respond, but to a lesser degree. Cells were analyzed in six independent experiments from three different clones. Data are reported as median ± interquartile range. P values between vehicle and TTX treatments were calculated via a Mann–Whitney U test. (D) AP morphology, as described by APD₉₀/APD₅₀ (ratio of action potential durations at 90% and 50% repolarization), shows a shift in distribution with increased time in culture. The horizontal line marks APD₉₀/APD₅₀ ratio of 1.4. Data for (A, B, D) were collected from four to seven independent differentiations per time range. Three clones from unrelated individuals are represented. White dots within each violin indicate medians and black rectangles indicate interquartile range. Days 11–13 of differentiation: n = 121 cells; D11–D14: n = 123; D17–D20: n = 88; D23–D27: n = 121; D32–D34: n = 102; D38–D42: n = 166. Following statistical analysis via a Kruskal–Wallis test, pairwise comparisons were performed using Dunn's test with Bonferroni adjustment. Significance of pairwise comparisons is presented as box color in the corresponding matrix for each parameter. hiPSC-CMs, human-induced pluripotent stem cell-derived cardiomyocytes; TTX, tetrodotoxin.