Stiffness and fraction of myosin motors responsible for active force in permeabilized muscle fibers from rabbit psoas
Stiffness and fraction of myosin motors responsible for active force in permeabilized muscle fibers from rabbit psoas
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DOI：
10.1529/biophysj.106.099549
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发表时间：
2007-04-01
影响因子：
3.4
通讯作者：
Lombardi, Vincenzo
中科院分区：
文献类型：
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作者：
Linari, Marco;Caremani, Marco;Lombardi, Vincenzo
单个肌球蛋白运动 (e) 的刚度是通过机械和热力学方法在兔腰肌的皮纤维中确定的。半肌节 (hs) 弹性应变的变化是通过快速力学测量的，无论是在所有肌球蛋白头都附着时，还是在主动收缩期间，通过改变 [Ca2+] 或温度来调节等长力 (T-0)。在饱和 [Ca2+] 时等长收缩中，hs 顺应性为 43.0 +/- 0.8 nm MPa-1，而在严格状态下，其为 28.2 +/- 1.1 nm MPa-1。肌丝的等效顺应性为 21.0 +/- 3.3 nm MPa-1。因此，在饱和 [Ca2+] ( e(0)) 时，附着在 hs 上的肌球蛋白头整体的刚度在等长收缩中为 45.5 +/- 1.7 kPa nm(-1)，而在严密性 ( er) 下，它会上升到 138.9 +/- 21.2 kPa nm(-1)。 e，根据 er 和晶格分子尺寸计算，为 1.21 +/- 0.18 pN nm(-1)。使用热力学方法，根据饱和 [ Ca2+] 时的 T-0 与绝对温度的倒数的关系估计为 1.25 +/- 0.14 pN nm(-1)，与估计的类似。严格地说。因此，比率 e(0)/e(r) (0.33 +/- 0.05) 可用于估计在饱和 [Ca2+] 时等长收缩期间附着头部的分数。如果使用渗透剂右旋糖酐T-500（4克/100毫升）来减少侧流。松弛纤维的纱距恢复到结皮前的值，e(0)和er均增加； 40%。 e 变为； 1.7 pN nm(-1) 并且在等长收缩中附着的肌球蛋白头的分数和力保持与应用葡聚糖之前相同。等长收缩时附着在肌动蛋白上的肌球蛋白头的比例为 0.33，这一发现排除了每次 ATP 水解存在多个机械循环的假设。
The stiffness of the single myosin motor ( e) is determined in skinned fibers from rabbit psoas muscle by both mechanical and thermodynamic approaches. Changes in the elastic strain of the half-sarcomere ( hs) are measured by fast mechanics both in rigor, when all myosin heads are attached, and during active contraction, with the isometric force ( T-0) modulated by changing either [ Ca2+] or temperature. The hs compliance is 43.0 +/- 0.8 nm MPa-1 in isometric contraction at saturating [ Ca2+], whereas in rigor it is 28.2 +/- 1.1 nm MPa-1. The equivalent compliance of myofilaments is 21.0 +/- 3.3 nm MPa-1. Accordingly, the stiffness of the ensemble of myosin heads attached in the hs is 45.5 +/- 1.7 kPa nm(-1) in isometric contraction at saturating [ Ca2+] ( e(0)), and in rigor ( er) it rises to 138.9 +/- 21.2 kPa nm(-1). e, calculated from er and the lattice molecular dimensions, is 1.21 +/- 0.18 pN nm(-1). e estimated, using a thermodynamic approach, from the relation of T-0 at saturating [ Ca2+] versus the reciprocal of absolute temperature is 1.25 +/- 0.14 pN nm(-1), similar to that estimated for. bers in rigor. Consequently, the ratio e(0)/e(r) ( 0.33 +/- 0.05) can be used to estimate the fraction of attached heads during isometric contraction at saturating [ Ca2+]. If the osmotic agent dextran T-500 ( 4 g/100 ml) is used to reduce the lateral. lament spacing of the relaxed fiber to the value before skinning, both e(0) and er increase by; 40%. e becomes; 1.7 pN nm(-1) and the fraction and the force of myosin heads attached in the isometric contraction remain the same as before dextran application. The finding that the fraction of myosin heads attached to actin in an isometric contraction is 0.33 rules out the hypothesis of multiple mechanical cycles per ATP hydrolyzed.