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Background and PurposeHeart failure can reflect impaired contractile function at the myofilament level. In healthy hearts, myofilaments become more sensitive to Ca2+as cells are stretched. This represents a fundamental property of the myocardium that contributes to the Frank–Starling response, although the molecular mechanisms underlying the effect remain unclear. Mavacamten, which binds to myosin, is under investigation as a potential therapy for heart disease. We investigated how mavacamten affects the sarcomere‐length dependence of Ca2+‐sensitive isometric contraction to determine how mavacamten might modulate the Frank–Starling mechanism. Experimental ApproachMulticellular preparations from the left ventricular‐free wall of hearts from organ donors were chemically permeabilized and Ca2+activated in the presence or absence of 0.5‐μM mavacamten at 1.9 or 2.3‐μm sarcomere length (37°C). Isometric force and frequency‐dependent viscoelastic myocardial stiffness measurements were made. Key ResultsAt both sarcomere lengths, mavacamten reduced maximal force and Ca2+sensitivity of contraction. In the presence and absence of mavacamten, Ca2+sensitivity of force increased as sarcomere length increased. This suggests that the length‐dependent activation response was maintained in human myocardium, even though mavacamten reduced Ca2+sensitivity. There were subtle effects of mavacamten reducing force values under relaxed conditions (pCa 8.0), as well as slowing myosin cross‐bridge recruitment and speeding cross‐bridge detachment under maximally activated conditions (pCa 4.5). Conclusion and ImplicationsMavacamten did not eliminate sarcomere length‐dependent increases in the Ca2+sensitivity of contraction in myocardial strips from organ donors at physiological temperature. Drugs that modulate myofilament function may be useful therapies for cardiomyopathies.
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Functional and structural differences between skinned and intact muscle preparations
Myofilaments and their associated proteins, which together constitute the sarcomeres, provide the molecular-level basis for contractile function in all muscle types. In intact muscle, sarcomere-level contraction is strongly coupled to other cellular subsystems, in particular the sarcolemmal membrane. Skinned muscle preparations (where the sarcolemma has been removed or permeabilized) are an experimental system designed to probe contractile mechanisms independently of the sarcolemma. Over the last few decades, experiments performed using permeabilized preparations have been invaluable for clarifying the understanding of contractile mechanisms in both skeletal and cardiac muscle. Today, the technique is increasingly harnessed for preclinical and/or pharmacological studies that seek to understand how interventions will impact intact muscle contraction. In this context, intrinsic functional and structural differences between skinned and intact muscle pose a major interpretational challenge. This review first surveys measurements that highlight these differences in terms of the sarcomere structure, passive and active tension generation, and calcium dependence. We then highlight the main practical challenges and caveats faced by experimentalists seeking to emulate the physiological conditions of intact muscle. Gaining an awareness of these complexities is essential for putting experiments in due perspective.
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- Award ID(s):
- 1653160
- PAR ID:
- 10361895
- Publisher / Repository:
- DOI PREFIX: 10.1085
- Date Published:
- Journal Name:
- Journal of General Physiology
- Volume:
- 154
- Issue:
- 2
- ISSN:
- 0022-1295
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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