Case Report on: Very Early Afterdepolarizations in HiPSC-Cardiomyocytes—An Artifact by Big Conductance Calcium Activated Potassium Current (Ibk,Ca)

Figures

• 

  Figure 1. Outward currents in C25 human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and the effect of iberiotoxin (IBTX). (A) Original outward traces before (black) and after (green) exposure of 100 nM IBTX in insensitive (upper, black directly underlying green curve) and sensitive (lower panel) hiPSC-CMs. (B–D). Summary of IBTX (100 nM) effects in insensitive (left panel) and sensitive (right panel) hiPSC-CMs quantified by area under the curve (B), peak current (C) and current at the end of the test pulse (late current, D). Mean values ± SEM. * p < 0.05, unpaired Student’s t test for basal values in insensitive vs. sensitive hiPSC-CMs; ## p < 0.01, ### p < 0.001; paired Student’s t test for basal vs. IBTX; n = number of isolated cells/number of individual differentiation batches.

• 

  Figure 2. Pronounced notch with oscillation in the plateau phase of action potential (AP) recorded from engineered heart tissue (EHT) derived by C25 human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). (A) Original AP recordings without (A) and with (B) notch followed by oscillating afterdepolarizations in EHT from cell line C25. (C) Summary of the results for take-off potential (TOP), AP amplitude (APA), maximum upstroke velocity (Vmax), AP duration at 90% repolarization (APD90), ** p < 0.01, unpaired Student’s t test; n = number of impalements/number of EHTs/number of individual differentiation batches.

• 

  Figure 3. Effects of iberiotoxin (IBTX) on action potentials (APs) in C25 engineered heart tissue (EHT) and in human left ventricular tissue (LV). Original AP recordings before and after exposure to IBTX (100 nM, green) in EHTs with (A) and without (B) notch/oscillations from cell line C25 and in LV (C). Mean values of AP duration at different levels of repolarization (APD10-90) before and after exposure to IBTX (100 nM) in EHTs with (D) and without (E) notch in cell line C25 and in LV (F). Mean values ± SEM, * p < 0.05, ** p < 0.01, paired Student’s t test.

• 

  Figure 4. Expression analysis for the alpha subunit (KCNMA1) of big conductance calcium activated potassium channel. Individual expression levels of KCNMA1 in left ventricular tissue (LV) and engineered heart tissue (EHT) from cell line C25 (without and with notch/oscillations), ERC018, iCell and iCell². Mean values ± SEM, *** p < 0.001, 1-way ANOVA with multiple comparison, n = number of patients for LV and n = number of EHT/number of individual differentiation batches.

• 

  Figure 5. Impact of including BKCa in a mathematical model of human ventricular cardiomyocytes. BKCa current (B) causes a deep notch in the action potential (A), and a substantial increase in the amplitude of L-type Ca2+ current (C).