The non-linear elasticity of the muscle sarcomere and the compliance of myosin motors
The non-linear elasticity of the muscle sarcomere and the compliance of myosin motors
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DOI：
10.1113/jphysiol.2013.265983
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发表时间：
2014-03-01
影响因子：
5.5
通讯作者：
Lombardi, Vincenzo
中科院分区：
文献类型：
--
作者：
Fusi, Luca;Brunello, Elisabetta;Lombardi, Vincenzo
关键点肌肉的功能单位半肌节（hs）中的力是由于平行排列在半肌球蛋白丝中的单个肌球蛋白马达的贡献，并拉动相对的肌动蛋白丝。根据线性hs模型，在等长收缩过程中，力上升到其最大稳定值（T-0），与肌动蛋白连接的马达的数量成比例，而hs应变上升的斜率取决于肌丝的顺应性。我们测量的HS刚度，叠加小4kHz的长度振荡的发展等长收缩，并发现了一个弹性元件平行于肌球蛋白马达具有恒定的刚度近似1/20的马达阵列在T-0。这些结果支持了肌球蛋白马达分布在多个亚状态中的结构模型，其中只有第一个亚状态在等长力产生期间被占据，导致大约1.7nm的马达应变。肌球蛋白马达平行作用的功能单位。机械和X射线结构证据表明，在等长收缩的平台（力T-0），不到一半的弹性应变的半肌节是由于应变的肌球蛋白马达阵列（S），与其余的被占占的细丝作为线性弹性元件与马达阵列串联。然而，在等长力发展的早期，已经发现半肌节顺应性小于上述假设的线性弹性模型的预期值，并且这种非线性可能影响s的估计。这个问题是研究在这里通过应用纳米微秒分辨率力学从青蛙骨骼肌在4摄氏度的单个完整的纤维，记录的力学性能的半肌节在等长收缩力的整个发展。结果解释与机械模型，以估计符合肌球蛋白马达。我们的结论如下：（1）在等长强直形成的早期，与肌球蛋白马达平行存在一个弹性元件，其顺应性约为200 nmMPa（-1）;（大约是T-0时电机阵列顺应性的20倍）;在等长收缩时，s为1.66 ± 0.05nm，与线弹性模型估计值无显著差异。
Key points The force in the half-sarcomere (hs), the functional unit of muscle, is due to the contributions of individual myosin motors arranged in parallel in the half-myosin filament and pulling on the opposing actin filament. According to a linear hs model, during an isometric contraction the force rises to its maximal steady value (T-0) in proportion to the number of actin-attached motors, while the hs strain rises with a slope that depends on the compliance of the myofilaments. We measured the hs stiffness, superimposing small 4kHz length oscillations on the development of isometric contraction, and found an elastic element in parallel to the myosin motors with a constant stiffness approximate to 1/20th that of the motor array at T-0. The results support a structural model in which myosin motors are distributed in multiple substates, of which only the first ones are occupied during isometric force generation, causing a motor strain of approximate to 1.7nm.AbstractForce in striated muscle is due to attachment of the heads of the myosin, the molecular motors extending from the myosin filament, to the actin filament in each half-sarcomere, the functional unit where myosin motors act in parallel. Mechanical and X-ray structural evidence indicates that at the plateau of isometric contraction (force T-0), less than half of the elastic strain of the half-sarcomere is due to the strain in the array of myosin motors (s), with the remainder being accounted for by the compliance of filaments acting as linear elastic elements in series with the motor array. Early during the development of isometric force, however, the half-sarcomere compliance has been found to be less than that expected from the linear elastic model assumed above, and this non-linearity may affect the estimate of s. This question is investigated here by applying nanometre-microsecond-resolution mechanics to single intact fibres from frog skeletal muscle at 4 degrees C, to record the mechanical properties of the half-sarcomere throughout the development of force in isometric contraction. The results are interpreted with mechanical models to estimate the compliance of the myosin motors. Our conclusions are as follows: (i)early during the development of an isometric tetanus, an elastic element is present in parallel with the myosin motors, with a compliance of approximate to 200nmMPa(-1) (approximate to 20times larger than the compliance of the motor array at T-0); and (ii)during isometric contraction, s is 1.66 +/- 0.05nm, which is not significantly different from the value estimated with the linear elastic model.