Different Segments within Vertebrate Muscles Can Operate on Different Regions of Their Force-Length Relationships
Different Segments within Vertebrate Muscles Can Operate on Different Regions of Their Force-Length Relationships
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DOI：
10.1093/icb/icy040
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发表时间：
2018-08-01
影响因子：
2.6
通讯作者：
Biewener, A. A.
中科院分区：
文献类型：
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作者：
Ahn, A. N.;Konow, N.;Biewener, A. A.
为了将肌肉内的肌束节段的体内行为与其体外力-长度关系联系起来，我们检查了三种脊椎动物肌肉中每一种肌肉内的成对节段的应变行为。在测定了美洲蟾蜍半膜肌（SM）的活体肌肉活动模式和长度变化后，（Bufo americanus）在跳跃过程中和大鼠胸骨舌骨肌（SH）内（Rattus rattus）在吞咽过程中，以及在小跑过程中大鼠内侧腓肠肌（MG）肌肉内空间分离的肌束，我们测量了它们相应的体外（蟾蜍）或原位（大鼠）力-长度关系（FLR）。对于所有三种肌肉，体内应变异质性持续约36-57%的行为周期，在此期间，一个段或束缩短，而另一个段或束同时延长。在蟾蜍SM中，近段从降支穿过其FLR的平台从其最佳长度（L-o）的1.12缩短至0.91，而远段在从0.94缩短至0.83 L-o之前延长（0.04 +/- 0.04 L-o）。在大鼠SH肌中，从0.90到0.85 L-o，近段在其升支上趋于缩短，而远段在L-o上趋于延长（0.96-1.12 L-o）。在大鼠MG肌肉中，近端肌束的体内应变范围为0.72至1.02 L-o，而远端肌束的应变范围为0.88至1.11 L-o。即使肌肉激活模式的时间段之间是相似的，在体内测量的肌束段的异质应变模式与不同的操作范围同时跨越其FLR，这意味着力-速度行为的差异。这三种脊椎动物骨骼肌代表了纤维结构和功能的多样性，并表明在一个肌肉区域中的FLR上的体内收缩应变和操作范围的模式不一定代表同一肌肉内的其他区域。
To relate in vivo behavior of fascicle segments within a muscle to their in vitro force-length relationships, we examined the strain behavior of paired segments within each of three vertebrate muscles. After determining in vivo muscle activity patterns and length changes of in-series segments within the semimembranosus muscle (SM) in the American Toad (Bufo americanus) during hopping and within the sternohyoid (SH) muscle in the rat (Rattus rattus) during swallowing, and of spatially separated fascicles within the medial gastrocnemius (MG) muscle in the rat during trotting, we measured their corresponding in vitro (toad) or in situ (rat) force-length relationships (FLRs). For all three muscles, in vivo strain heterogeneity lasted for about 36-57% of the behavior cycle, during which one segment or fascicle shortened while the other segment or fascicle simultaneously lengthened. In the toad SM, the proximal segment shortened from the descending limb across the plateau of its FLR from 1.12 to 0.91 of its optimal length (L-o), while the distal segment lengthened (by 0.04 +/- 0.04 L-o) before shortening down the ascending limb from 0.94 to 0.83 L-o. In the rat SH muscle, the proximal segment tended to shorten on its ascending limb from 0.90 to 0.85 L-o while the distal segment tended to lengthen across L-o (0.96-1.12 L-o). In the rat MG muscle, in vivo strains of proximal fascicles ranged from 0.72 to 1.02 L-o, while the distal fascicles ranged from 0.88 to 1.11 L-o. Even though the timing of muscle activation patterns were similar between segments, the heterogeneous strain patterns of fascicle segments measured in vivo coincided with different operating ranges across their FLRs simultaneously, implying differences in force-velocity behavior as well. The three vertebrate skeletal muscles represent a diversity of fiber architectures and functions and suggest that patterns of in vivo contractile strain and the operating range over the FLR in one muscle region does not necessarily represent other regions within the same muscle.