Key result
Rat epicardial and midmyocardial slices show higher active and passive stretch tension than the endocardium.
Why the study?
Determining transmural mechanical properties helps understand cardiac mechanics, but the mechanical profile of living individual cardiac layers had not been examined.
Intact myocardial slices from rats reveal intrinsic transmural heterogeneity in cardiac mechanics, with epicardium and midmyocardium showing higher active and passive tension than endocardium.
Highlights need for layer-specific myocardial studies; leaves open translation to human cardiac mechanics and disease.
Determining transmural mechanical properties in the heart provides a foundation to understand physiological and pathophysiological cardiac mechanics. Although work on mechanical characterisation has begun in isolated cells and permeabilised samples, the mechanical profile of living individual cardiac layers has not been examined. Myocardial slices are 300 μm-thin sections of heart tissue with preserved cellular stoichiometry, extracellular matrix, and structural architecture. This allows for cardiac mechanics assays in the context of an intact in vitro organotypic preparation. In slices obtained from the subendocardium, midmyocardium and subepicardium of rats, a distinct pattern in transmural contractility is found that is different from that observed in other models. Slices from the epicardium and midmyocardium had a higher active tension and passive tension than the endocardium upon stretch. Differences in total myocyte area coverage, and aspect ratio between layers underlined the functional readouts, while no differences were found in total sarcomeric protein and phosphoprotein between layers. Such intrinsic heterogeneity may orchestrate the normal pumping of the heart in the presence of transmural strain and sarcomere length gradients in the in vivo heart.
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Pitoulis et al. (2020) studied this question. Epicardial and midmyocardial slices vs. Endocardial slices was evaluated on Active and passive tension upon stretch. Myocardial slices from the epicardium and midmyocardium of rats demonstrated higher active and passive tension upon stretch compared to the endocardium.
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