Gulati J, Babu A
Biophys J. 1985 Nov;48(5):781-7. doi: 10.1016/S0006-3495(85)83836-4.
Force development by skinned frog semitendinosus fibers was studied at various levels of lateral compression to compare the results with intact fibers and to evaluate the limits on cross-bridge movements during isometric contraction. The skinned fibers were compressed osmotically using a high molecular weight polymer, dextran T500. Ca-activated force remained constant down to 58% of the fiber width (w0) after skinning, corresponding to a nearly twofold change in separation between the thin and thick filaments in the myofilament lattice. This agrees with the earlier result on intact fibers, and gives additional evidence that the cross-bridge mechanism for force generation is relatively insensitive to large changes in interfilament separation. Further compression, below 0.58 w0, produced a sharp drop in force, and the force was practically zero at a fiber width of 50%. The effect at high compression was the same at all pCa's, which indicates that the Ca sensitivity of the myofilaments is unaffected by radial compression. The stiffness of the fiber remained high in rigor in the presence of dextran, which indicates that the rigor cross-bridge attachment is not inhibited, and actually may be improved, with decreases in the interfilament space. Also, the drop in active force with the highest compression was similar when the compressed fibers were put in rigor before contraction, which suggests that the force drop also was not due to a hindrance to cross-bridge attachment. The results appear to exclude large motions such as tilting and rocking of the bridge as a rigid molecule, but suggest that at least some molecular movement is essential for force development; they also raise the possibility that there is a critical interfilament separation in the fiber, below which the cross-bridge cannot function.
研究了经皮剥制的青蛙半腱肌纤维在不同侧向压缩水平下的力发展情况，以将结果与完整纤维进行比较，并评估等长收缩过程中横桥运动的限制。使用高分子量聚合物葡聚糖T500对等长收缩过程中横桥运动的限制。使用高分子量聚合物葡聚糖T500对等长收缩过程中横桥运动的限制。使用高分子量聚合物葡聚糖T500对经皮剥制的纤维进行渗透压压缩。去皮肤后，钙激活的力在纤维宽度（w0）的58%以下保持恒定，这对应于肌丝晶格中细肌丝和粗肌丝之间间距的近两倍变化。这与早期对完整纤维的研究结果一致，并提供了额外证据，表明产生力的横桥机制对肌丝间间距的大幅变化相对不敏感。进一步压缩至低于0.58 w0时，力急剧下降，在纤维宽度为50%时力几乎为零。在所有pCa值下，高压缩时的效果相同，这表明肌丝的钙敏感性不受径向压缩的影响。在存在葡聚糖的情况下，纤维在强直收缩时的刚度仍然很高，这表明强直横桥附着不受抑制，实际上随着肌丝间空间的减小可能会得到改善。此外，当压缩纤维在收缩前进入强直收缩状态时，最高压缩下的主动力下降情况相似，这表明力的下降也不是由于横桥附着受阻。结果似乎排除了桥作为刚性分子的大幅运动，如倾斜和摇摆，但表明至少一些分子运动对于力的发展是必不可少的；它们还增加了纤维中存在临界肌丝间间距的可能性，低于该间距横桥无法发挥作用。
