Innovative Method for Dual Visualization of Electrical and Calcium Activity in Heart Muscle Cells

Researchers from Kyoto University, in partnership with Takeda Pharmaceutical Company, have unveiled a groundbreaking technique to simultaneously capture action potentials (APs) and calcium transients in single cardiomyocytes derived from patient-specific induced pluripotent stem cells (iPSCs). This advancement, published in Frontiers in Physiology, promises to enhance the understanding of cardiac arrhythmias, particularly catecholaminergic polymorphic ventricular tachycardia (CPVT).

CPVT is a rare and potentially fatal inherited condition characterized by abnormal calcium handling in heart muscle cells. While iPSC-derived cardiomyocytes have frequently been utilized to model CPVT and assess drug responses, prior research has primarily focused on either APs or calcium transients independently. This limitation hampers comprehensive insights into the interactions between electrical signals and calcium dynamics that contribute to arrhythmias.

To address this gap, the research team integrated a dual-dye approach employing the membrane potential dye FluoVolt and the newly developed calcium indicator Calbryte 590 AM. This innovative combination offers a superior signal-to-noise ratio compared to traditional methods, facilitating long-term, simultaneous imaging of both APs and calcium waveforms in individual cells. Moreover, the researchers optimized light intensity and filter settings to reduce phototoxicity while enhancing detection accuracy.

The study involved analyzing cardiomyocytes derived from a patient with CPVT type 1 (RyR2-I4587V). The findings revealed that approximately two-thirds of the cardiomyocytes, resembling ventricular cells, exhibited abnormal calcium transients, including double peaks, triple peaks, and oscillations, significantly more than healthy control cells. These observations align with the recognized pathophysiology associated with CPVT.

The team further assessed the effects of various pharmacological agents on these abnormal cardiomyocytes. Carvedilol, a nonselective ?-blocker, demonstrated improvements in calcium abnormalities at concentrations ranging from 1-3 µM, although higher doses led to atrial-like APs or asystole. Flecainide, a class 1C antiarrhythmic drug, proved moderately effective at doses between 1-10 µM, consistent with clinical findings. JTV519 (K201), a modulator of RyR2, significantly improved calcium irregularities at a concentration of 3 µM, albeit with alterations in AP morphology. Notably, the CaMKII inhibitor KN-93 exhibited remarkable efficacy, normalizing calcium transients in 93% of cells at a concentration of 1 µM without adversely affecting APs.

This innovative methodology allows for the comprehensive monitoring of electrical and calcium dynamics in patient-derived cardiomyocytes, providing a more relevant platform for evaluating drug responses. It holds the potential to facilitate the development of safer, more effective treatments tailored to individual patients, as well as to identify novel therapeutic strategies for challenging arrhythmias.

Significantly, this represents one of the first successful attempts to achieve stable, long-term dual imaging in single human iPSC-derived cardiomyocytes. Beyond CPVT, the technique could be adapted for the investigation of other cardiac disorders and drug-induced arrhythmias, laying the groundwork for future advancements in precision cardiology.