Ca2+-Currents in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Effects of Two Different Culture Conditions

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) provide a unique opportunity to study human heart physiology and pharmacology and repair injured hearts. The suitability of hiPSC-CM critically depends on how closely they share physiological properties of human adult cardiomyocytes (CM). Here we investigated whether a 3D engineered heart tissue (EHT) culture format favors maturation and addressed the L-type Ca2+-current (I-Ca,I-L) as a readout. The results were compared with hiPSC-CM cultured in conventional monolayer (ML) and to our previous data from human adult atrial and ventricular CM obtained when identical patch-clamp protocols were used. HiPSC-CM were two- to three-fold smaller than adult CM, independently of culture format [capacitance ML 45 +/- 1 pF (n = 289), EHT 45 +/- 1 pF (n = 460), atrial CM 87 +/- 3 pF (n = 196), ventricular CM 126 +/- 8 pF (n = 50)]. Only 88% of ML cells showed ICa, but all EHT. Basal ICa density was 10 +/- 1 pA/pF (n = 207) for ML and 12 +/- 1 pA/pF (n = 361) for EHT and was larger than in adult CM [7 +/- 1 pA/pF (p < 0.05, n = 196) for atrial CM and 6 +/- 1 pA/pF (p < 0.05, n = 47) for ventricular CM]. However, ML and EHT showed robust T-type Ca2+-currents (I-Ca,I-T). While (-)-Bay K 8644, that activates I-Ca,I-L directly, increased I-Ca,I-L to the same extent in ML and EHT, beta 1- and beta 2-adrenoceptor effects were marginal in ML, but of same size as (-)-Bay K 8644 in EHT. The opposite was true for serotonin receptors. Sensitivity to beta 1 and beta 2-adrenoceptor stimulation was the same in EHT as in adult CM (-logEC50: 5.9 and 6.1 for norepinephrine (NE) and epinephrine (Epi), respectively), but very low concentrations of Rp-8-Br-cAMPS were sufficient to suppress effects (-logEC50: 5.3 and 5.3 respectively for NE and Epi). Taken together, hiPSC-CM express ICa,L at the same density as human adult CM, but, in contrast, possess robust I-Ca,I-T. Increased effects of catecholamines in EHT suggest more efficient maturation.