Functional and structural differences between skinned and intact muscle preparations

Abstract

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.

Advancing clinical translation of cardiac biomechanics models: a comprehensive review, applications and future pathways

“…This experimental system allows for a more direct characterisation and control of sarcomere biomechanical reactions than can be inferred from intact cells. However, the interpretation of these measurements in the context of intact cells faces significant challenges [ 25 ]. To a large extent, the interpretation of the measurements themselves often necessarily rests on model-based assumptions.…”

“…The underlying assumption of skinned muscle measurements is that the structural and molecular features of the myofilament system are sufficiently preserved to reproduce the essential functional properties and behaviour of the original system. However, in reality, there are notable discrepancies between the skinned and intact systems, which make the translation of the measurements of the skinned system into their physiological context challenging [ 25 ]. Nonetheless, skinned muscle preparations are widely used to provide quantitative information about active tension properties and cardiac cell kinetics.…”

Alterations of the skeletal muscle contractile apparatus in necrosis induced by myotoxic snake venom phospholipases A2: a mini-review

“…Snake venom-induced myotoxicity is due to the action of a variety of venom components, mainly secreted phospholipase A 2 (PLA 2 ) enzymes, PLA 2 homologs devoid of enzymatic activity, matrix-degrading metalloproteinases, and a group of low molecular mass myotoxins having homology with β-defensins (Harris and Cullen 1990 ; Gutierrez and Ownby 2003 ; Lomonte 2023 ). By far, the most important myotoxic components in snake venoms are PLA 2 s and PLA 2 homologs (Gutierrez and Ownby 2003 ; Lomonte and Križaj 2021 ).…”

“…Since these toxins induce a synchronous pattern of muscle damage, they have become useful tools for studying the cellular processes involved in skeletal muscle degeneration and regeneration (Harris and Cullen 1990 ; Harris 2003 ). In particular, myotoxic PLA 2 s and PLA 2 homologs from the venoms of the species Bothrops asper (family Viperidae, group II secreted PLA 2 s) and Notechis scutatus (family Elapidae, group I secreted PLA 2 s) have been extensively used in these investigations, although studies with other similar toxins have been also carried out (Dixon and Harris 1996 ; Gutierrez and Ownby 2003 ; Lomonte 2023 ). Some of these myotoxins are catalytically-active Asp-49 enzymes that cleave the sn -2 ester bond in phospholipids, while PLA 2 homologs (also referred to as PLA 2 -like myotoxins) display mutations in residue 49 and other residues of the so-called calcium-binding loop, thus rendering these proteins enzymatically inactive, although keeping the ability to damage muscle fibers (Francis et al 1991 ; Ward et al 2002 ; Gutierrez and Ownby 2003 ; Lomonte and Rangel 2012 ).…”

“…The mechanism of action of myotoxic PLA 2 s and PLA 2 homologs has been investigated by using a variety of experimental models (rodent in vivo tests, ex vivo muscle preparations and isolated cells, intravital microscopy, cell culture models, and phospholipid vesicles) (Dixon and Harris 1996 ; Gutierrez and Ownby 2003 ; Lomonte 2023 ). These investigations have shown that the first stage in the action of these toxins is the binding to the skeletal muscle plasma membrane, followed by the disruption of the integrity of muscle sarcolemma, either by enzymatic degradation of phospholipids or by a catalytically-independent destabilization of the membrane (Dixon and Harris 1996 ; Fernandez et al 2013 ; Fernandes et al 2014 ).…”