Higher sensitivity to ouabain-induced toxicity in hiPSC-cardiomyocytes than human adult heart tissue despite similar Na+/K+-ATPase pump current amplitudes

D. Ismaili (Hamburg)¹, P. Virtanen (Tampere)², J. Im (Hamburg)³, P. Brunnbauer (Hamburg)³, U. Saleem (Hamburg)³, M. Sönmez (Hamburg)⁴, C. Schulz (Hamburg)⁵, M. Nandudu (Hamburg)³, J. Winters (Maastricht)⁶, C. E. Molina (Hamburg)⁷, J. Petersen (Hamburg)⁸, M. Stoll (Münster)⁹, U. Schotten (Maastricht)¹⁰, A. Hansen (Hamburg)⁴, T. Eschenhagen (Hamburg)¹¹, J. Koivumäki (Tampere)¹², T. Christ (Hamburg)^11
1Universitäres Herz- und Gefäßzentrum Hamburg Klinik für Kardiologie Hamburg, Deutschland; ²Tampere, Finnland; ³Hamburg, Deutschland; ⁴Universitätsklinikum Hamburg-Eppendorf Institut für Experimentelle Pharmakologie und Toxikologie Hamburg, Deutschland; ⁵Universitäres Herz- und Gefäßzentrum Hamburg Hamburg, Deutschland; ⁶Maastricht University Faculty of Health, Medicine and Life Sciences Maastricht, Niederlande; ⁷Universitätsklinikum Hamburg-Eppendorf Zentrum für Experimentelle Medizin, Experimentelle Herz-Kreislaufforschung Hamburg, Deutschland; ⁸Universitäres Herz- und Gefäßzentrum Klinik und Poliklinik für Herz- und Gefäßchirurgie Hamburg, Deutschland; ⁹Universitätsklinikum Münster Institut für Humangenetik, Abt. Genetische Epidemiologie Münster, Deutschland; ¹⁰Maastricht UMC+Heart+Vascular Center Dept. of Physiology Maastricht, Niederlande; ¹¹Universitätsklinikum Hamburg-Eppendorf Institut für Klinische Pharmakologie und Toxikologie Hamburg, Deutschland; ¹²BioMediTech, Faculty of Medicine and Health Technology, Tampere University Tampere, Finnland

Background and Purpose: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) have gained interest as a pharmacological model. However, ongoing concern about the immaturity of hiPSC-CM leads to uncertainty regarding translation to adult human heart. Here, we studied the properties of the key player in maintaining ionic homeostasis, the Na⁺/K⁺-ATPase (NKA), in hiPSC-CM.

Experimental Approach: Atrial and ventricular engineered heart tissues (EHTs) were produced from hiPSC-CMs. For comparison, adult atrial and ventricular tissues were obtained from patients undergoing open heart surgery. We measured NKA gene expression, NKA pump currents (I_NKA) and ouabain effects on action potentials and contractility. Computational modelling was used to further investigate the direct and indirect impacts of NKA inhibition.

Key Results: The mRNA abundance of the major NKA isoforms was higher in ventricular than atrial CM (both adult and hiPSC-CM). Consistently, I_NKA was also higher in ventricular than in atrial hiPSC-CM (1.32±0.1 pA/pF vs. 0.92±0.09 pA/pF, p < 0.05) and higher in ventricular than in atrial adult CM (1.44±0.1 pA/pF vs. 1.04±0.07 pA/pF, p < 0.05). The potency of ouabain to block I_NKA did not differ between hiPSC-derived and adult CM. Ouabain shortened plateau phase in both EHT and adult tissue. However, lower ouabain concentrations than in adult human tissue depolarized diastolic potential and depressed force in EHTs, demonstrating a higher integrated sensitivity to NKA inhibition. Computational modelling indicated that lower I_K1 (as typically seen in hiPSC-CM) increases the susceptibility to depolarization by NKA, a mechanism also characteristic of Purkinje fibres.

Conclusions and Implications: Our findings indicate that hiPSC-EHTs express NKA with biophysical characteristics and functions that are not different from adult human tissue. The higher sensitivity of EHTs to depolarize under ouabain-induced block of NKA suggests that their electrophysiological properties more closely resemble Purkinje fibres than working myocardium.