Chen J S, Baskin R J, Baskin R J, Burton K, Shen S, Yeh Y
Department of Zoology, University of California, Davis 95616.
Biophys J. 1989 Sep;56(3):595-605. doi: 10.1016/S0006-3495(89)82706-7.
Measurement of the state of optical polarization of light diffracted from single, skinned and intact fibers of anterior tibialis muscle from Rana pipiens revealed a dependence upon rigor, activation, and sarcomere length (SL) change. Changes in total birefringence, delta nT, and differential field ratio value, rT, were determined. In a relaxed, skinned fiber the total birefringence value, delta nT, decreases as sarcomere length is increased from 2.1 microns to approximately 2.8-3.0 microns. From there it increases significantly to a value of approximately 1.8 x 10(-3) at a sarcomere length of 3.6 microns. The differential field ratio, rT, also shows a biphasic response to increasing sarcomere length, first exhibiting a rapid decrease over shorter SL and leveling out after the SL is beyond 3.0 microns. In comparison, relaxed intact fibers change substantially less upon sarcomere length change, showing little change in birefringence and a small bi-phasic change in rT. Skinned fibers were activated using a solution that has the same ionic strength as the relaxing solution and allows repeatable, and sustained activation. A decrease in both delta nT and rT was observed upon fiber activation. The decrease in delta nT and rT was slightly larger at shorter sarcomere lengths than at longer lengths. Relaxed fibers placed in rigor showed changes in delta nT and rT similar to those observed in activated fibers. These results are consistent with the hypothesis that, after activation, a significant portion of the thick filament cross-bridges rotate towards the actin filament resulting in redistribution of the interfilament mass content. They are also consistent with an average orientation of crossbridges in the overlap region different from that in the nonoverlap region.
对豹蛙胫前肌单根、去皮和完整纤维衍射光的光学偏振状态进行测量，结果显示其与强直、激活以及肌节长度（SL）变化有关。测定了总双折射变化量（δnT）和微分场比值（rT）。在松弛的去皮纤维中，当肌节长度从2.1微米增加到约2.8 - 3.0微米时，总双折射值δnT降低。此后，在肌节长度为3.6微米时，它显著增加至约1.8×10⁻³的值。微分场比值rT对肌节长度增加也呈现双相响应，首先在较短的SL范围内快速下降，在SL超过3.0微米后趋于平稳。相比之下，松弛的完整纤维在肌节长度变化时变化要小得多，双折射变化很小，rT有小的双相变化。使用与松弛溶液离子强度相同的溶液激活去皮纤维，可实现可重复且持续的激活效果。纤维激活后，观察到δnT和rT均下降。在较短肌节长度时，δnT和rT的下降幅度略大于较长肌节长度时。置于强直状态的松弛纤维显示出的δnT和rT变化与激活纤维中观察到的变化相似。这些结果与以下假设一致：激活后，大部分粗肌丝横桥向肌动蛋白丝旋转，导致丝间质量含量重新分布。它们也与重叠区域横桥的平均取向与非重叠区域不同这一观点一致。
