The heart on a chip: the role of realistic mathematical models of cardiac electrical activity in understanding and treating cardiac arrhythmias

New Modalities of 3D Pluripotent Stem Cell-Based Assays in Cardiovascular Toxicity

The substantial progress of the human induced pluripotent stem cell (hiPSC) technologies over the last decade has provided us with new opportunities for cardiovascular drug discovery, regenerative medicine, and disease modeling. The combination of hiPSC with 3D culture techniques offers numerous advantages for generating and studying physiological and pathophysiological cardiac models. Cells grown in 3D can overcome many limitations of 2D cell cultures and animal models. Furthermore, it enables the investigation in an architecturally appropriate, complex cellular environment in vitro. Yet, generation and study of cardiac organoids-which may contain versatile cardiovascular cell types differentiated from hiPSC-remain a challenge. The large-scale and high-throughput applications require accurate and standardised models with highly automated processes in culturing, imaging and data collection. Besides the compound spatial structure of organoids, their biological processes also possess different temporal dynamics which require other methods and technologies to detect them. In this review, we summarise the possibilities and challenges of acquiring relevant information from 3D cardiovascular models. We focus on the opportunities during different time-scale processes in dynamic pharmacological experiments and discuss the putative steps toward one-size-fits-all assays.

Sex-specific IKAS activation in rabbit ventricles with drug-induced QT prolongation

BACKGROUND

Female sex is a known risk factor for drug-induced long QT syndrome (diLQTS). We recently demonstrated a sex difference in apamin-sensitive small-conductance Ca2+-activated K+ current (IKAS) activation during β-adrenergic stimulation.

OBJECTIVE

The purpose of this study was to test the hypothesis that there is a sex difference in IKAS in the rabbit models of diLQTS.

METHODS

We evaluated the sex difference in ventricular repolarization in 15 male and 22 female Langendorff-perfused rabbit hearts with optical mapping techniques during atrial pacing. HMR1556 (slowly activating delayed rectifier K+ current [IKs] blocker), E4031 (rapidly activating delayed rectifier K+ current [IKr] blocker) and sea anemone toxin (ATX-II, late Na+ current [INaL] activator) were used to simulate types 1-3 long QT syndrome, respectively. Apamin, an IKAS blocker, was then added to determine the magnitude of further QT prolongation.

RESULTS

HMR1556, E4031, and ATX-II led to the prolongation of action potential duration at 80% repolarization (APD80) in both male and female ventricles at pacing cycle lengths of 300-400 ms. Apamin further prolonged APD80 (pacing cycle length 350 ms) from 187.8±4.3 to 206.9±7.1 (P=.014) in HMR1556-treated, from 209.9±7.8 to 224.9±7.8 (P=.003) in E4031-treated, and from 174.3±3.3 to 188.1±3.0 (P=.0002) in ATX-II-treated female hearts. Apamin did not further prolong the APD80 in male hearts. The Cai transient duration (CaiTD) was significantly longer in diLQTS than baseline but without sex differences. Apamin did not change CaiTD.

CONCLUSION

We conclude that IKAS is abundantly increased in female but not in male ventricles with diLQTS. Increased IKAS helps preserve the repolarization reserve in female ventricles treated with IKs and IKr blockers or INaL activators.