Baskin R J, Lieber R L, Oba T, Yeh Y
Biophys J. 1981 Dec;36(3):759-73. doi: 10.1016/S0006-3495(81)84764-9.
In a recently developed theory of light diffraction by single striated muscle fibers, we considered only the case of normal beam incidence. The present investigation represents both an experimental and theoretical extension of the previous work to arbitrary incident angle. Angle scan profiles over a 50 degrees range of incident angle (+25 degrees to -25 degrees) were obtained at different sarcomere lengths. Left and right first-order scan peak separations were found to be a function of sarcomere length (separation angle = 2 theta B), and good agreement was found between theory and experiment. Our theoretical analysis further showed that a myofibrillar population with a single common skew angle can yield an angle scan profile containing many peaks. Thus, it is not necessary to associate each peak with a different skew population. Finally, we have found that symmetry angle, theta s, also varies with sarcomere length, but not in a regular manner. Its value at a given sarcomere length is a function of a particular region of a given fiber and represents the average skew angle of all the myofibril populations illuminated. The intensity of a diffraction order line is considered to be principally the resultant of two interference phenomena. The first is a volume-grating phenomenon which results from the periodic A-I band structure of the fiber (with some contribution from Z bands and H zones). The second is Bragg reflection from skew planes, if the correct relation between incident angle and skew angle is met. This may result in intensity asymmetry between the left and right first order lines.
在最近发展的关于单根横纹肌纤维光衍射的理论中，我们仅考虑了光束正入射的情况。本研究是对先前工作在任意入射角方面的实验和理论扩展。在不同肌节长度下获得了入射角在50度范围（+25度至 -25度）内的角度扫描轮廓。发现左右一阶扫描峰间距是肌节长度的函数（间距角 = 2θB），并且理论与实验之间取得了良好的一致性。我们的理论分析进一步表明，具有单一公共倾斜角的肌原纤维群体可以产生包含许多峰的角度扫描轮廓。因此，不必将每个峰与不同的倾斜群体相关联。最后，我们发现对称角θs也随肌节长度而变化，但并非呈规则方式。在给定肌节长度下其值是给定纤维特定区域的函数，并且代表所有被照亮的肌原纤维群体的平均倾斜角。衍射级线的强度主要被认为是两种干涉现象的结果。第一种是由纤维的周期性A - I带结构（Z带和H区也有一些贡献）导致的体光栅现象。第二种是如果满足入射角和倾斜角之间的正确关系，则来自倾斜平面的布拉格反射。这可能导致左右一阶线之间的强度不对称。
