Ward Samuel R, Winters Taylor M, O'Connor Shawn M, Lieber Richard L
Department of Bioengineering, University of California, San Diego, San Diego, CA, United States.
Department of Orthopaedic Surgery, University of California, San Diego, San Diego, CA, United States.
Front Physiol. 2020 Mar 20;11:211. doi: 10.3389/fphys.2020.00211. eCollection 2020.
Defining variations in skeletal muscle passive mechanical properties at different size scales ranging from single muscle fibers to whole muscles is required in order to understand passive muscle function. It is also of interest from a muscle structural point-of-view to identify the source(s) of passive tension that function at each scale. Thus, we measured passive mechanical properties of single fibers, fiber bundles, fascicles, and whole muscles in three architecturally diverse muscles from New Zealand White rabbits ( = 6) subjected to linear deformation. Passive modulus was quantified at sarcomere lengths across the muscle's anatomical range. Titin molecular mass and collagen content were also quantified at each size scale, and whole muscle architectural properties were measured. Passive modulus increased non-linearly from fiber to whole muscle for all three muscles emphasizing extracellular sources of passive tension ( < 0.001), and was different among muscles ( < 0.001), with significant muscle by size-scale interaction, indicating quantitatively different scaling for each muscle ( < 0.001). These findings provide insight into the structural basis of passive tension and suggest that the extracellular matrix (ECM) is the dominant contributor to whole muscle and fascicle passive tension. They also demonstrate that caution should be used when inferring whole muscle properties from reduced muscle size preparations such as muscle biopsies.
为了理解肌肉的被动功能，需要确定从单根肌纤维到整块肌肉等不同尺寸尺度下骨骼肌被动力学特性的变化。从肌肉结构的角度来看，确定在每个尺度下起作用的被动张力来源也很有意义。因此，我们测量了来自新西兰白兔（ = 6）的三种结构不同的肌肉中，单根纤维、纤维束、肌束和整块肌肉在受到线性变形时的被动力学特性。在肌肉解剖范围内的肌节长度处对被动模量进行了量化。还在每个尺寸尺度上对肌联蛋白分子量和胶原蛋白含量进行了量化，并测量了整块肌肉的结构特性。对于所有三块肌肉，被动模量从纤维到整块肌肉呈非线性增加，强调了被动张力的细胞外来源（ < 0.001），并且在不同肌肉之间存在差异（ < 0.001），存在显著的肌肉与尺寸尺度的相互作用，表明每块肌肉的缩放比例在数量上有所不同（ < 0.001）。这些发现为被动张力的结构基础提供了见解，并表明细胞外基质（ECM）是整块肌肉和肌束被动张力的主要贡献者。它们还表明，在从诸如肌肉活检等缩小尺寸的肌肉标本推断整块肌肉特性时应谨慎。
