(H-298) Triple-parametric optical mapping to measure cardiac metabolism-excitation-contraction coupling in healthy and diseased hearts

Introduction:: Introduction: Cardiac function is routinely assessed by measuring electrical rhythms, mechanics, or metabolism. However, these three aspects of cardiac physiology are interdependent and cannot be studied separately. We recently developed triple-parametric optical mapping to measure metabolism-excitation-contraction coupling (MECC) in the heart, which allows the study of the relationship between these three facets of cardiac physiology.

Exercise therapy is routinely applied in patients with heart diseases. While this is associated with improving cardiac mechanical function, little was known about the other aspects of cardiac function. Here we applied triple-parametric optical mapping to characterize the effects of moderate-intensity endurance exercise on cardiac MECC during anti-cancer chemotherapy with doxorubicin (DOX).


Materials and Methods:: Materials and Methods: Male and female C57BL/6J mice were divided into four groups 1) Control -sedentary, 2) exercise (EX) – run on a treadmill at 1 km/hr for 45 mins/day, 5 days/week, for 6 weeks, 3) DOX – treated with DOX at 5 mg/kg for 6 weeks, and 4) EXDOX – subjected to both EX and DOX treatments. At the end of the study period, mice were euthanized, and triple-parametric optical mapping was performed to measure transmembrane potential (electrical excitation), intracellular calcium (contraction), and NADH (metabolism). Hearts were stained with voltage-sensitive (RH237) and calcium indicator (Rhod2-AM) dyes. The dyes and NADH autofluorescence were excited by light at 520 and 365 nm, respectively, and the emitted light was collected using three CMOS cameras at 1 kHz. Arrhythmia inducibility was determined by applying burst pacing protocols.


Results, Conclusions, and Discussions:: Results: Action potentials and calcium transients, the electrical and intracellular calcium signatures of a single heartbeat, were recorded, and ten cardiac function parameters were measured under each condition.

In female mice, action potential duration (APD) prolongation was the most prominent effect of treatments. APD was prolonged by EX (21%), DOX (29%), and EXDOX (18%) treatments. Additionally, longitudinal conduction velocity (CVL) of electrical impulse propagation was increased by EXDOX treatment in female mice. These changes in cardiac electrical function correlated with increased arrhythmia risk in EX and EXDOX groups, with 100% arrhythmia inducibility in EX and 50% in EXDOX groups.

In male mice, DOX treatment increased calcium rise time (Ca RT, 36%), which is the duration of calcium release versus control. EXDOX treatment induced further modulation of MECC. Specifically, an increase in the rise time of action potential (Vm RT, 9%), Ca RT (42%), and APD (14%) were observed in male EXDOX hearts versus control. Arrhythmia risk was increased in all three groups, EX, DOX, and EXDOX versus control (100%, 83%, and 83%, respectively).

Conclusions: EX, DOX, and EXDOX treatments, all modulate cardiac function. While these treatments modulated only cardiac electrical function in female mice, both electrical and mechanical (calcium) functions were altered in males. Further investigation is needed to determine the effects of exercise and DOX on metabolic function.

Discussions: In this study, we implemented triple-parametric optical mapping to perform a complete characterization of cardiac physiology modulation by exercise therapy. Importantly, we demonstrate that exercise therapy during DOX chemotherapy modulates MECC in a sex-dimorphic manner. Specifically, male mice demonstrated most changes in cardiac function parameters that are associated with increased arrhythmia risk. These results indicate the modulation of specific aspects of cardiac physiology that underlie increased arrhythmia risk in mice during exercise and DOX therapy.


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