Tidball J G
Biophys J. 1986 Dec;50(6):1127-38. doi: 10.1016/S0006-3495(86)83557-3.
We subjected single skeletal muscle cells from frog semitendinosus to sinusoidal oscillations that simulated the strain experienced as the cells near the end of passive extension and begin active contraction in slow swimming. Other cells from which the basement membrane was removed by enzymatic and mechanical procedures were tested identically. Effectiveness of the basement membrane removal technique was evaluated by electron microscopy, by an electrophoretic and lectin-binding assay for depletion of cell surface glycoproteins, and by confirmation by means of electrophoretic and immunologic analyses that major intracellular, cytoskeletal proteins were not disrupted. Measurements of maximum stress, maximum strain, and phase lag between these maxima enabled the complex modulus (dynamic stiffness) and loss tangent (relative viscous losses to elastic energy storage) to be calculated for each mechanically tested preparation. We also calculated the amounts of energy stored and dissipated in each preparation. These calculations indicate that cells with intact basement membranes have complex moduli significantly greater than those of cells without basement membranes, and that cells with basement membrane store significantly more elastic energy than basement membrane depleted cells. However, when subjected to identical sinusoidal strains, energy dissipation in cells with intact basement membranes is over three times greater than dissipation in cells without basement membrane. The relative magnitudes of energy losses to energy storage, called the specific loss, is nearly three times greater for intact cells than for basement membrane depleted cells. Basement membranes may thereby serve as a brake for slowing passive extension of muscle before contraction begins.
我们使来自青蛙半腱肌的单个骨骼肌细胞经受正弦振荡，该振荡模拟了细胞在被动伸展接近尾声并开始缓慢游泳中的主动收缩时所经历的应变。对通过酶促和机械程序去除基底膜的其他细胞进行了相同的测试。通过电子显微镜、用于检测细胞表面糖蛋白消耗的电泳和凝集素结合试验，以及通过电泳和免疫分析确认主要的细胞内细胞骨架蛋白未被破坏，来评估基底膜去除技术的有效性。测量最大应力、最大应变以及这些最大值之间的相位滞后，使得能够为每个经过机械测试的制剂计算复数模量（动态刚度）和损耗角正切（相对于弹性能量储存的粘性损耗）。我们还计算了每个制剂中储存和耗散的能量。这些计算表明，具有完整基底膜的细胞的复数模量明显大于没有基底膜的细胞，并且具有基底膜的细胞比去除基底膜的细胞储存的弹性能量明显更多。然而，当经受相同的正弦应变时，具有完整基底膜的细胞中的能量耗散比没有基底膜的细胞中的能量耗散大三倍以上。能量损失与能量储存的相对大小，即比损耗，完整细胞几乎是去除基底膜细胞的三倍。因此，基底膜可能起到一种制动作用，在收缩开始前减缓肌肉的被动伸展。
