Candia Carnevali M D, Saita A, Fedrigo A
J Muscle Res Cell Motil. 1986 Dec;7(6):568-78. doi: 10.1007/BF01753572.
The peculiar functional structure of the Z-line in the obliquely striated muscles of some feather stars is described. It is known that cross-striated muscles are characterized by linear and continuous Z-bands, and obliquely striated muscles by disconnected, obliquely aligned Z-elements. Owing to this discontinuous organization, the sarcomere can perform wide active lengthenings, shortenings, and even 'super-elongations' in the helical fibres. In contrast, the obliquely striated fibres of crinoids show markedly continuous and homogeneous oblique Z-lines; such a structure is not compatible with 'super-performances' like sliding and shearing of the sarcomere elements, but instead could allow functions comparable to those characteristic of a cross-striated muscle (quick, short movements, mechanically amplifiable by bone levers). This odd situation, only interpretable in terms of evolutionary constraint, could be considered opposite and symmetrical to that of cross-striated 'super-contracting' muscles, where the Z-line is exceptionally fragmented to allow the sarcomere to super-contract. The possible architecture of a significant parameter such as the Z-line, which determines muscle fibre potential capacities, is analysed in detail: through qualitative-quantitative evaluation of electron micrographs, supported by statistical analysis of the data; and by computer simulations. The data obtained suggest that the most realistic conformation of the whole Z-complex in these muscles consists of a multiple system of continuous, ribbon-like helical planes running in parallel along the fibre from end to end and regularly cutting it with a constant thickness. The proposed model seems morphologically compatible with the experimentally verified situations and functionally compatible with the mechanical requirements for a normal contraction and for a balanced distribution of the involved strengths.
描述了某些海百合斜纹肌中Z线独特的功能结构。已知横纹肌的特征是线性且连续的Z带，而斜纹肌的特征是不连续、倾斜排列的Z元件。由于这种不连续的组织，肌节在螺旋纤维中可以进行大幅度的主动伸长、缩短，甚至“超伸长”。相比之下，海百合的斜纹纤维显示出明显连续且均匀的倾斜Z线；这种结构与肌节元件的滑动和剪切等“超性能”不兼容，但可能允许具有与横纹肌特征相当的功能（快速、短距离运动，可通过骨杠杆进行机械放大）。这种奇特的情况，只能从进化限制的角度来解释，可以被认为与横纹“超收缩”肌肉的情况相反且对称，在横纹“超收缩”肌肉中，Z线异常碎片化以允许肌节进行超收缩。详细分析了一个重要参数（如决定肌纤维潜在能力的Z线）的可能结构：通过对电子显微镜照片进行定性 - 定量评估，并辅以数据的统计分析；以及通过计算机模拟。所获得的数据表明，这些肌肉中整个Z复合体最现实的构象由多个连续的、带状螺旋平面系统组成，这些平面沿着纤维从头到尾平行排列，并以恒定厚度有规律地切割纤维。所提出的模型在形态上似乎与实验验证的情况兼容，在功能上与正常收缩以及相关力量平衡分布的机械要求兼容。
