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

Abstract

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent an unlimited source of human CMs that could be a standard tool in drug research. However, there is concern whether hiPSC-CMs express all cardiac ion channels at physiological level and whether they might express non-cardiac ion channels. In a control hiPSC line, we found large, “noisy” outward K+ currents, when we measured outward potassium currents in isolated hiPSC-CMs. Currents were sensitive to iberiotoxin, the selective blocker of big conductance Ca2+-activated K+ current (IBK,Ca). Seven of 16 individual differentiation batches showed a strong initial repolarization in the action potentials (AP) recorded from engineered heart tissue (EHT) followed by very early afterdepolarizations, sometimes even with consecutive oscillations. Iberiotoxin stopped oscillations and normalized AP shape, but had no effect in other EHTs without oscillations or in human left ventricular tissue (LV). Expression levels of the alpha-subunit (KCa1.1) of the BKCa correlated with the presence of oscillations in hiPSC-CMs and was not detectable in LV. Taken together, individual batches of hiPSC-CMs can express sarcolemmal ion channels that are otherwise not found in the human heart, resulting in oscillating afterdepolarizations in the AP. HiPSC-CMs should be screened for expression of non-cardiac ion channels before being applied to drug research.

Modeling Cardiovascular Diseases with hiPSC-Derived Cardiomyocytes in 2D and 3D Cultures

“…Finally, despite the achievement of crucial goals in hiPS-CMs differentiation and maturation, as well as in 3D construct generation, it should be noticed that the growing body of work we are now witnessing at times shows conflicting data, likely due to the lack of hiPS-CMs quality control and standardized experimental conditions among different studies. In this regard, a fitting example is represented by electrophysiology studies; in this context, there are examples of hiPS-CMs showing a lack of ion currents normally observed in adult cells [87,179], but also of hiPS-CMs expressing ion channels that are absent in adult cardiomyocytes [110,180]. This consideration underlines the importance of carefully evaluating the expression of cardiomyocyte-specific ion channels in hiPS-CMs before considering a particular model for electrophysiology and/or therapeutic studies.…”

Ion channel expression and electrophysiology of singular human (primary and induced pluripotent stem cell derived) cardiomyocytes

“…Therefore, drug-induced changes of integrative parameters, need to be interpreted with the caveat that a set of ion channels different from the expected physiological one might contribute to these parameters in the hiPSC-CM model system being used. A previous case report even describes the presence of a non-cardiac ion channel current in individual batches of hiPSC-CMs (Horváth et al, 2020). Thus, for the analysis of integrative parameters, primary cardiomyocytes might be preferable.…”

Inhibition of BKCa channels protects neonatal hearts against myocardial ischemia and reperfusion injury

“…Ectopic expression of the BK Ca channel in murine HL-1 cardiomyocytes indicates that the introduction of BK Ca shortens the action potential duration [38]. In human iPSC-derived cardiomyocytes, the BK Ca channel induces irregular action potential shapes resembling very early afterdepolarizations [26]. On these lines, we performed an in silico simulation on cardiac action potential (AP) in presence of the BK Ca channel.…”

“…Potassium currents measured in the plasma membrane of cardiomyocytes from 10-12 days old chick embryos exhibited all the hallmarks of the BK Ca channel properties such as: large single-channel conductance, voltage, and Ca 2+ dependence and sensitivity to tetramethylammonium (TEA)-and charybdotoxin [25]. Additionally, human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs), showed sensitivity to IbTx treatment that shifted membrane polarization towards more positive potentials and caused a disturbance in action potential wave which was not observed in cardiomyocytes isolated from the adult human left ventricle [26]. However, the precise role and impact of BK Ca channels in the plasma membrane of cardiomyocytes during the early stages of development are not yet elucidated.…”