Image-based evaluation of contraction–relaxation kinetics of human-induced pluripotent stem cell-derived cardiomyocytes: Correlation and complementarity with extracellular electrophysiology

AbstractIn this study, we used high-speed video microscopy with motion vector analysis to investigate the contractile characteristics of hiPS-CM monolayer, in addition to further characterizing the motion with extracellular field potential (FP), traction force and the Ca2+ transient. Results of our traction force microscopy demonstrated that the force development of hiPS-CMs correlated well with the cellular deformation detected by the video microscopy with motion vector analysis. In the presence of verapamil and isoproterenol, contractile motion of hiPS-CMs showed alteration in accordance with the changes in fluorescence peak of the Ca2+ transient, i.e., upstroke, decay, amplitude and full-width at half-maximum. Simultaneously recorded hiPS-CM motion and FP showed that there was a linear correlation between changes in the motion and field potential duration in response to verapamil (30–150nM), isoproterenol (0.1–10μM) and E-4031 (10–50nM). In addition, tetrodotoxin (3–30μM)-induced delay of sodium current was corresponded with the delay of the contraction onset of hiPS-CMs. These results indicate that the electrophysiological and functional behaviors of hiPS-CMs are quantitatively reflected in the contractile motion detected by this image-based technique. In the presence of 100nM E-4031, the occurrence of early after-depolarization-like negative deflection in FP was also detected in the hiPS-CM motion as a characteristic two-step relaxation pattern. These findings offer insights into the interpretation of the motion kinetics of the hiPS-CMs, and are relevant for understanding electrical and mechanical relationship in hiPS-CMs

A deep learning algorithm to translate and classify cardiac electrophysiology

The development of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) has been a critical in vitro advance in the study of patient-specific physiology, pathophysiology, and pharmacology. We designed a new deep learning multitask network approach intended to address the low throughput, high variability, and immature phenotype of the iPSC-CM platform. The rationale for combining translation and classification tasks is because the most likely application of the deep learning technology we describe here is to translate iPSC-CMs following application of a perturbation. The deep learning network was trained using simulated action potential (AP) data and applied to classify cells into the drug-free and drugged categories and to predict the impact of electrophysiological perturbation across the continuum of aging from the immature iPSC-CMs to the adult ventricular myocytes. The phase of the AP extremely sensitive to perturbation due to a steep rise of the membrane resistance was found to contain the key information required for successful network multitasking. We also demonstrated successful translation of both experimental and simulated iPSC-CM AP data validating our network by prediction of experimental drug-induced effects on adult cardiomyocyte APs by the latter

Comparison of V̇O2 for buoyancy and propulsion during swimming between male and female

体脂肪は人体の水中体重を小さくするから, 水泳には体脂肪の多いことが有利な条件となる可能性がある。本研究は水泳の際に浮くために使われるV̇O2と推進のために使われるV̇O2を測定し, 水中体重の大小が実際の水泳にどれほどの影響を与えているかという点について検討したものである。 男女各3名, 計6名の泳者に, 泳速が0.6, 0.8及び1.0m/secのクロール泳を行わせ, V̇O2を測定した。その際腰に錘をつけて水中体重を増加させ, あるいは滑車を介した錘で腰を引き上げるようにして水中体重を減少させ, 各水中体重において上記の測定を行った。V̇O2値を水中体重に対してプロットすることによって得られる回帰直線の勾配から浮くためのV̇O2を, またY切片から安静時V̇O2を差し引くことによって推進のためのV̇O2を求めた。 1 浮くために必要なV̇O2は泳速とは無関係であり, その平均値は男子の方(352±140ml/min)が女子のそれ(186±83ml/min)より有意に大であった。この差は水中体重に大きく依存していて, 単位水中体重当りに換算すると男女の値は接近した(男子: 117±46ml/min, 女子: 91±36ml/min)。 2 推進のために用いられるV̇O2は, 泳速の増加に伴って指数関数的に増大した。その増加率は男子よりも女子の方が大であったが, それは女子の水泳能力が男子のそれより劣ることに関連していると考えられる。 3 総V̇O2に対する推進のためのV̇O2の割合は, 男子よりも女子において大きく, この点女子の水中体重の小さいことは水泳において有利な条件になっている。男子の世界記録に対する女子のそれの比率は, 競泳の場合には競走の場合より大きいが, この差は女子の体脂肪の多いことが水泳では有利に作用していることに由来するものと考えられる。Body fat lessens underwater body weight and may offer an advantage for swimming performance. The present study was undertaken to measure separately V̇O2 for buoyancy and that for propulsion during swimming in the swimming flume and to elucidate the advantage of lower underwater body weight in female. Three male swimmers and three female swimmers participated as the subjects. V̇O2 was measured during free style swimming at a constant speed of 0.6, 0.8 and l.0m/sec.Underwater weight was increased stepwisely by loading an extra-weight around the subject's waist or decreased by suspending a weight which pulls the waist upward via a wire and pulleies. V̇O2 at a given speed depended proportionally on the underwater weight. V̇O2 for propu1sion was estimated by subtracting resting V̇O2 from the intercept on the ordinate, and V̇O2 for buoyancy was calculated from the slope. 1) V̇O2 for buoyancy was independent of swimming speed and the average value for female swimmers was much smaller than that for male swimmers (352±140m1/min for male, 186±83m1/min for female). This difference in V̇O2 for buoyancy depended largely on the difference in underwater weight as the calculated values of V̇O2 for buoyancy per kg of underwater weight revealed much smaller difference between sexes (117±46m1/min for male, 91±36m1/min for female). 2) V̇O2 for propulsion increased exponentially with increasing speed. The increasing rate was larger in female than in male. This is probably because of relative inferiority of swimming ability in the female group in this study. 3) The rate of propulsion V̇O2 to total V̇O2 during swimming was larger in female than in male. This represents the advantage of lower underwater weight in female for swimming. This result offers the probable explanation for the discrepancy which exists in male-female ratio of the world records between swimming and running

A computational model of induced pluripotent stem-cell derived cardiomyocytes incorporating experimental variability from multiple data sources

KEY POINTS: Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) capture patient-specific genotype-phenotype relationships, as well as cell-to-cell variability of cardiac electrical activity Computational modelling and simulation provide a high throughput approach to reconcile multiple datasets describing physiological variability, and also identify vulnerable parameter regimes We have developed a whole-cell model of iPSC-CMs, composed of single exponential voltage-dependent gating variable rate constants, parameterized to fit experimental iPSC-CM outputs We have utilized experimental data across multiple laboratories to model experimental variability and investigate subcellular phenotypic mechanisms in iPSC-CMs This framework links molecular mechanisms to cellular-level outputs by revealing unique subsets of model parameters linked to known iPSC-CM phenotypes ABSTRACT: There is a profound need to develop a strategy for predicting patient-to-patient vulnerability in the emergence of cardiac arrhythmia. A promising in vitro method to address patient-specific proclivity to cardiac disease utilizes induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). A major strength of this approach is that iPSC-CMs contain donor genetic information and therefore capture patient-specific genotype-phenotype relationships. A cited detriment of iPSC-CMs is the cell-to-cell variability observed in electrical activity. We postulated, however, that cell-to-cell variability may constitute a strength when appropriately utilized in a computational framework to build cell populations that can be employed to identify phenotypic mechanisms and pinpoint key sensitive parameters. Thus, we have exploited variation in experimental data across multiple laboratories to develop a computational framework for investigating subcellular phenotypic mechanisms. We have developed a whole-cell model of iPSC-CMs composed of simple model components comprising ion channel models with single exponential voltage-dependent gating variable rate constants, parameterized to fit experimental iPSC-CM data for all major ionic currents. By optimizing ionic current model parameters to multiple experimental datasets, we incorporate experimentally-observed variability in the ionic currents. The resulting population of cellular models predicts robust inter-subject variability in iPSC-CMs. This approach links molecular mechanisms to known cellular-level iPSC-CM phenotypes, as shown by comparing immature and mature subpopulations of models to analyse the contributing factors underlying each phenotype. In the future, the presented models can be readily expanded to include genetic mutations and pharmacological interventions for studying the mechanisms of rare events, such as arrhythmia triggers.S

Circulating KCNH2 Current-Activating Factor in Patients with Heart Failure and Ventricular Tachyarrhythmia

It is estimated that approximately half of the deaths in patients with HF are sudden and that the most likely causes of sudden death are lethal ventricular tachyarrhythmias such as ventricular tachycardia (VT) or fibrillation (VF). However, the precise mechanism of ventricular tachyarrhythmias remains unknown. The KCNH2 channel conducting the delayed rectifier K(+) current (I(Kr)) is recognized as the most susceptible channel in acquired long QT syndrome. Recent findings have revealed that not only suppression but also enhancement of I(Kr) increase vulnerability to major arrhythmic events, as seen in short QT syndrome. Therefore, we investigated the existence of a circulating KCNH2 current-modifying factor in patients with HF.We examined the effects of serum of HF patients on recombinant I(Kr) recorded from HEK 293 cells stably expressing KCNH2 by using the whole-cell patch-clamp technique. Study subjects were 14 patients with non-ischemic HF and 6 normal controls. Seven patients had a history of documented ventricular tachyarrhythmias (VT: 7 and VF: 1). Overnight treatment with 2% serum obtained from HF patients with ventricular arrhythmia resulted in a significant enhancement in the peaks of I(Kr) tail currents compared to the serum from normal controls and HF patients without ventricular arrhythmia.Here we provide the first evidence for the presence of a circulating KCNH2 channel activator in patients with HF and ventricular tachyarrhythmias. This factor may be responsible for arhythmogenesis in patients with HF

Acute Effects of Sex Steroid Hormones on Susceptibility to Cardiac Arrhythmias: A Simulation Study

Acute effects of sex steroid hormones likely contribute to the observation that post-pubescent males have shorter QT intervals than females. However, the specific role for hormones in modulating cardiac electrophysiological parameters and arrhythmia vulnerability is unclear. Here we use a computational modeling approach to incorporate experimentally measured effects of physiological concentrations of testosterone, estrogen and progesterone on cardiac ion channel targets. We then study the hormone effects on ventricular cell and tissue dynamics comprised of Faber-Rudy computational models. The “female” model predicts changes in action potential duration (APD) at different stages of the menstrual cycle that are consistent with clinically observed QT interval fluctuations. The “male” model predicts shortening of APD and QT interval at physiological testosterone concentrations. The model suggests increased susceptibility to drug-induced arrhythmia when estradiol levels are high, while testosterone and progesterone are apparently protective. Simulations predict the effects of sex steroid hormones on clinically observed QT intervals and reveal mechanisms of estrogen-mediated susceptibility to prolongation of QT interval. The simulations also indicate that acute effects of estrogen are not alone sufficient to cause arrhythmia triggers and explain the increased risk of females to Torsades de Pointes. Our results suggest that acute effects of sex steroid hormones on cardiac ion channels are sufficient to account for some aspects of gender specific susceptibility to long-QT linked arrhythmias