Relative expression of fetal (slow skeletal) and adult (cardiac) troponin I isoforms in hiPSC-CMs. (A) Western blot showing the expression of the fetal isoform of troponin I (slow skeletal troponin I [ssTnI]). Shown are four lysates from WT cells (W1, W2, W3, and W4) and four lysates from R92Q cells (R1, R2, R3, and R4). GAPDH is used as a loading control. (B) Western blot on a separate membrane showing the expression of the adult isoform of troponin I (cardiac troponin I [cTnI]). Shown are four lysates from WT cells (W1, W2, W3, and W4) and four lysates from R92Q cells (R1, R2, R3, and R4). GAPDH is used as a loading control. (C) Quantification of the ratio of ssTnI/cTnI was determined by densitometry. The TnI/GAPDH ratio was calculated for both ssTnI and cTnI and then divided to get the ratio. These is no difference in the ratio (ns, not significant [P = 0.49] by Mann–Whitney test).