Cardiomyocytes generated from embryonic stem cells (ESCs) and induced pluripotent stem (iPS) cells are suggested for repopulation of destroyed myocardium. Because contractile properties are crucial for functional regeneration, we compared cardiomyocytes differentiated from ES cells (ESC-CMs) and iPS cells (iPS-CMs). Native myocardium served as control. Murine ESCs or iPS cells were differentiated 11 d in vitro and cocultured 5-7 d with irreversibly injured myocardial tissue slices. Vital embryonic ventricular tissue slices of similar age served for comparison. Force-frequency relationship (FFR), effects of Ca(2+), Ni(2+), nifedipine, ryanodine, beta-adrenergic, and muscarinic modulation were studied during loaded contractions. FFR was negative for ESC-CMs and iPS-CMs. FFR was positive for embryonic tissue and turned negative after treatment with ryanodine. In all groups, force of contraction and relaxation time increased with the concentration of Ca(2+) and decreased with nifedipine. Force was reduced by Ni(2+). Isoproterenol (1 microM) increased the force most pronounced in embryonic tissue (207+/-31%, n=7; ESC-CMs: 123+/-5%, n=4; iPS-CMs: 120+/-4%, n=8). EC(50) values were similar. Contractile properties of iPS-CMs and ESC-CMs were similar, but they were significantly different from ventricular tissue of comparable age. The results indicate immaturity of the sarcoplasmic reticulum and the beta-adrenergic response of iPS-CMs and ESC-CMs.

Abstract-In the present study, we investigated the electrophysiological maturation and integration of immature cardiomyocytes after transplantation; maturation and integration are essential to achieve the cardiac regeneration. Murine fetal cardiomyocytes (FCMs) (d12.5-d15.5) expressing enhanced green fluorescent protein under the control of the ␣-actin promoter were injected into cryoinjured areas and adjacent myocardium of cryoinjured mouse ventricles. Viable short axis tissue slices (thickness, 150 m) of the ventricles were prepared 5 to 6 days after transplantation. Glass microelectrodes were used for measurements of action potentials in transplanted FCMs and host cardiomyocytes within the slices. Stimulation at frequencies of up to 10 Hz was performed via a unipolar electrode placed in viable host tissue. Transplanted FCMs could be distinguished clearly from host tissue by their green fluorescence and their electrophysiological properties: maximal upstroke velocity (V max ) was significantly lower and action potential duration at 50% repolarization (APD 50 ) was significantly longer compared with values of adult cardiomyocytes. Transplanted FCMs surrounded by cryoinjured tissue showed spontaneous electrical and contractile activity, which was in no case synchronous with host tissue. V max and APD 50 of these nonintegrated cells matched values of cultivated dissociated FCMs. In contrast, 82% of transplanted FCMs surrounded by viable host tissue were electrically integrated; ie, electrical and contractile activity was synchronous with host tissue and these cells had more mature action potential parameters (significantly higher V max and shorter APD 50 ) compared with nonintegrated FCMs. In conclusion, electrophysiological maturation and integration of transplanted FCMs depend on an embedment in viable host myocardium. Key Words: cardiac electrophysiology Ⅲ cardiomyoplasty Ⅲ coupling Ⅲ heart slices Ⅲ maturation A cute myocardial infarction and chronic heart failure are among the most frequent causes of morbidity and mortality in Western countries. In the course of physiological reparation processes, cardiomyocytes lost because of myocardial infarction are replaced by scar tissue, leading to an impaired cardiac function and remodeling of the remaining myocardium. Despite advances in the conventional therapy, this loss of functional myocardium remains irreversible. Thus, there is a strong need for a novel therapeutic approach aiming at a regeneration of cardiomyocytes: cardiac cell therapy.Cardiomyocytes derived from embryonic stem cells (ESCCMs) are promising candidates for cell therapy via an exogenic replacement of lost cardiomyocytes, because their cardiac phenotype, including cardiac specific protein expression as well as typical cardiac electrophysiological properties, is undoubted. 1 Clinical studies using ESC-CMs have not been performed, because, first, techniques enabling the production and selection of sufficient cell numbers must be developed and potential risks and immunological issues must be investi...

Aims: Induced pluripotent stem (iPS) cells have a developmental potential similar to that of blastocyst-derived embryonic stem (ES) cells and may serve as an autologous source of cells for tissue repair, in vitro disease modelling and toxicity assays. Here we aimed at generating iPS cell-derived cardiomyocytes (CMs) and comparing their molecular and functional characteristics with CMs derived from native murine ES cells. Methods and Results: Beating cardiomyocytes were generated using a mass culture system from murine N10 and O9 iPS cells as well as R1 and D3 ES cells. Transcripts of the mesoderm specification factor T-brachyury and non-atrial cardiac specific genes were expressed in differentiating iPS EBs. Using immunocytochemistry to determine the expression and intracellular organisation of cardiac specific structural proteins we demonstrate strong similarity between iPS-CMs and ES-CMs. In line with a previous study electrophysiological analyses showed that hormonal response to β-adrenergic and muscarinic receptor stimulation was intact. Action potential (AP) recordings suggested that most iPS-CMs measured up to day 23 of differentiation are of ventricular-like type. Application of lidocaine, Cs⁺, SEA0400 and verapamil+ nifedipine to plated iPS-EBs during multi-electrode array (MEA) measurements of extracellular field potentials and intracellular sharp electrode recordings of APs revealed the presence of I_Na, I_f, I_NCX, and I_CaL, respectively, and suggested their involvement in cardiac pacemaking, with I_CaL being of major importance. Furthermore, iPS-CMs developed and conferred force to avitalized ventricular tissue that was responsive to β-adrenergic stimulation. Conclusions: Our data demonstrate that the cardiogenic potential of iPS cells is comparable to that of ES cells and that iPS-CMs possess all fundamental functional elements of a typical cardiac cell, including spontaneous beating, hormonal regulation, cardiac ion channel expression and contractility. Therefore, iPS-CMs can be regarded as a potentially valuable source of cells for in vitro studies and cellular cardiomyoplasty.

Cardiac experimental electrophysiology is in need of a well-defined Minimum Information Standard for recording, annotating, and reporting experimental data. As a step toward establishing this, we present a draft standard, called Minimum Information about a Cardiac Electrophysiology Experiment (MICEE). The ultimate goal is to develop a useful tool for cardiac electrophysiologists which facilitates and improves dissemination of the minimum information necessary for reproduction of cardiac electrophysiology research, allowing for easier comparison and utilisation of findings by others. It is hoped that this will enhance the integration of individual results into experimental, computational, and conceptual models. In its present form, this draft is intended for assessment and development by the research community. We invite the reader to join this effort, and, if deemed productive, implement the Minimum Information about a Cardiac Electrophysiology Experiment standard in their own work.