Force and Calcium Transients Analysis in Human Engineered Heart Tissues Reveals Positive Force-Frequency Relation at Physiological Frequency

Force measurements in ex vivo and engineered heart tissues are well established. Analysis of calcium transients (CaT) is complementary to force, and the combined analysis is meaningful to the study of cardiomyocyte biology and disease. This article describes a model of human induced pluripotent stem cell cardiomyocyte-derived engineered heart tissues (hiPSC-CM EHTs) transduced with the calcium sensor GCaMP6f followed by sequential analysis of force and CaT. Average peak analysis demonstrated the temporal sequence of the CaT preceding the contraction twitch. The pharmacological relevance of the test system was demonstrated with inotropic indicator compounds. Force-frequency relationship was analyzed in the presence of ivabradine (300 nM), which reduced spontaneous frequency and unmasked a positive correlation of force and CaT at physiological human heart beating frequency with stimulation frequency between 0.75 and 2.5 Hz (force +96%; CaT +102%). This work demonstrates the usefulness of combined force/CaT analysis and demonstrates a positive force-frequency relationship in hiPSC-CM EHTs. •Analysis of calcium transients and force in engineered heart tissues•Accurate replications of drug effects on calcium transients and force analysis•Positive force- and calcium transients-frequency relationship•Reverse correlation between omecamtiv mecarbil's inotropic effect and frequency In this article, Hansen and colleagues establish a system using human induced pluripotent stem cell-derived cardiomyocytes to sequentially analyze force and calcium transients (CaTs) in an engineered heart tissue model by using genetically encoded calcium indicator (GCaMP6f) and demonstrate a positive force- and CaT-frequency relationship at physiological human heart beat frequencies.