Cooke P H, Kargacin G, Craig R, Fogarty K, Fay F S
Department of Anatomy, University of Massachusetts, Medical School, Worcester 01605.
Prog Clin Biol Res. 1987;245:1-25.
The contractile elements of single, skinned amphibian smooth muscle cells were resolved as fibrils containing F-actin and side-polar myosin filaments and adjacent cytoplasmic dense bodies, containing alpha-actinin and actin. The fibrils were found to be linked axially through actin filaments to the dense bodies, by electron microscopy. The arrangement of these two structures provides the essential features of a sarcomere to the contractile elements. The effect of contraction upon the movement of the dense bodies was followed dynamically by optical microscopy as a method of analyzing the organization of the contractile apparatus and resolving contractile units. Averaged over long time periods (30 to 50 seconds), the axial movements of dense bodies was uniform. The dense bodies were not simply displaced passively during contraction because the extent of radial movements averaged over the same (long) time periods were less than would be expected for the observed increases in cell diameter. Measured over short time intervals (3 to 6 seconds), the axial movement of some closely spaced dense bodies was not uniform: individual and groups of bodies moved significantly faster and slower than the mean rate of axial translocation. These shifts in coordinated and independent movements might reveal separate anisometric contractile units, or they could represent a random temporal pattern of localized activation and deactivation of small contractile elements.
单个剥制的两栖类平滑肌细胞的收缩元件被解析为含有F-肌动蛋白和侧极肌球蛋白丝的原纤维，以及相邻的含α-辅肌动蛋白和肌动蛋白的胞质致密体。通过电子显微镜观察发现，原纤维通过肌动蛋白丝轴向连接到致密体。这两种结构的排列为收缩元件提供了肌节的基本特征。通过光学显微镜动态跟踪收缩对致密体运动的影响，以此作为分析收缩装置组织和解析收缩单位的一种方法。在较长时间段（30至50秒）内进行平均，致密体的轴向运动是均匀的。致密体在收缩过程中并非简单地被动移位，因为在相同（长）时间段内平均的径向运动程度小于观察到的细胞直径增加所预期的程度。在短时间间隔（3至6秒）内测量时，一些紧密排列的致密体的轴向运动并不均匀：单个或成组的致密体移动速度明显快于或慢于轴向移位的平均速率。这些协调和独立运动的变化可能揭示了单独的非等长收缩单位，或者它们可能代表了小收缩元件局部激活和失活的随机时间模式。
