Ca(2+)-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 Ca(2+)-current (I(Ca,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 I(Ca), but all EHT. Basal I(Ca) 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 Ca(2+)-currents (I(Ca,T)). While (−)-Bay K 8644, that activates I(Ca,L) directly, increased I(Ca,L)to the same extent in ML and EHT, β(1)- and β(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 β(1) and β(2)-adrenoceptor stimulation was the same in EHT as in adult CM (−logEC(50): 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 (−logEC(50): 5.3 and 5.3 respectively for NE and Epi). Taken together, hiPSC-CM express I(Ca,L) at the same density as human adult CM, but, in contrast, possess robust I(Ca,T). Increased effects of catecholamines in EHT suggest more efficient maturation.