Journal Article

BS48 Insights into the frank-starling behaviour and mechanical vulnerability of isolated adult cardiomyocytes: a single-cell work-loop contractility study

Tran, Patrick, Linekar Adam, Banerjee. Prithwish, Sham, Shelley, Maddock, Helen, Hurst, Josh

2025

Overview

BackgroundUnderstanding cellular mechanisms driving heart failure (HF) progression requires characterisation of cardiomyocyte mechanics under varying loading conditions. While traditional isometric experiments offer limited insight into the dynamic cardiac function, work-loops models provide a more physiologically relevant framework for studying cardiac mechanics in-vitro. We employ a work-loop technique to examine myocyte mechanics under both physiological and pathological load, investigating the Frank-Starling relationship at a cellular level and the impact of high mechanical stress on cardiomyocyte function and structure.MethodsIsolated adult rat ventricular myocytes (n=15) were attached to a piezo-translator and force transducer (IonOptix, Milton, USA) and subjected to both isometric and workloop contractions at increasing sarcomere lengths (preload) at 1 Hz. Work-loops were configured with a preload of 10% and afterload of 50% of developed isometric force. Developed force and stroke work were averaged from ten stable traces. A high-preload protocol (paced at 3 Hz) was used to simulate volume overloaded conditions. Stroke work (area within the work-loop) was continuously monitored. Isometric force and cell morphology were measured pre- and post-experiment. Bathing solution was carefully replaced without disrupting cell position to assess for potential recovery.ResultsMyocytes exhibited exponential force augmentation with stretch, with a mean 3.45-fold (±0.58 SD) increase, but stretching beyond 2.2µM led to cell instability and death (figure 1A). Similarly, stroke work increased significantly from 1.7µm to 2.15µM, with a 5.42-fold (±0.96SD) rise from baseline (figure 1B). However, stable workloops could not be maintained at 2.2µM due to pro-arrhythmic behaviour or cell detachment from vigorous force-length changes. No optimal length plateau was demonstrated, unlike multicellular or in-vivo preparations. Under sustained high-preload conditions, significant mechanical deterioration was observed (30.3% force reduction. p=0.0012) within 8–10 minutes of stressed work-loops, accompanied by membrane blebbing and cellular distortion (figure 2). Buffer replacement or cell rest did not restore cellular function, indicating irreversible damage under pathologically high preload conditions.Abstract BS48 Figure 1(A) Developed Force of contraction as a function of sarcomeric length from 1.7 to 2.2µM (n=5 rats); (B) Stroke work from work-loops as a function of sarcomeric length with corresponding work-loops from 1.7 to 2.15µM sarcomeric lengths (n=5 rats)[Image Omitted. See PDF.]Abstract BS48 Figure 2(A) Series of high preload workloops at 3 Hz demonstrating a significant reduction in stroke work (area within work loop) over time; (B) Significant functional and structural impairment of the myocyte seen before and after the high preload mechanical stress (n=5 rats)[Image Omitted. See PDF.]ConclusionThis study shows that isolated cardiomyocytes, devoid of their natural extracellular matrix support, become vulnerable to irreversible damage when stretched beyond 2.2µM sarcomeric length. The mechanical vulnerability to brief periods of excessive preload supports the notion that sustained myocyte overdistension in volume-overloaded hearts can lead to irreversible cellular damage, potentially contributing to irreversible heart failure and replacement fibrosis. These results emphasize the importance of early intervention to reverse pathologically high stress to enhance the possibility of myocardial reverse remodelling and potential recovery.

• Publisher: BMJ Publishing Group LTD
• Subject: Cardiomyocytes / Heart failure / Mechanics