Okamura N, Ishiwata S
Department of Physics, School of Science and Engineering, Waseda University, Tokyo, Japan.
J Muscle Res Cell Motil. 1988 Apr;9(2):111-9. doi: 10.1007/BF01773733.
We found that the lengths of all sarcomeres spontaneously oscillated in an isolated skeletal myofibril, when both ends were fixed, submillimolar to millimolar concentrations of ATP, ADP and inorganic phosphate (Pi) were present, and Ca2+ was removed. Narrowing and widening of an H-zone and an I-band were observed corresponding to the shortening and lengthening of a sarcomere, suggesting that thick and thin filaments slide past each other. The oscillation of each sarcomere was asymmetrical, consisting of a rapid lengthening phase and a slow shortening phase. The period of oscillation was about 3s; the peak-to-peak amplitude of oscillation reached as much as 30% of the average sarcomere length. The propagation of the sarcomere oscillation along the long axis of the myofibril was observed occasionally in single myofibrils and frequently in bundles of myofibrils. The 'state'-diagram showing the concentration range of ADP and Pi in which contraction, oscillation or relaxation of myofibrils occurs in the presence of ATP and the absence of Ca2+ suggested that the oscillation is a third state of skeletal muscle located in between the contracting and relaxing states.
我们发现，在两端固定、存在亚毫摩尔至毫摩尔浓度的ATP、ADP和无机磷酸盐（Pi）且去除Ca2+的情况下，分离出的骨骼肌肌原纤维中所有肌节的长度会自发振荡。观察到H带和I带的变窄和变宽分别对应肌节的缩短和延长，这表明粗肌丝和细肌丝相互滑动。每个肌节的振荡是不对称的，由快速延长阶段和缓慢缩短阶段组成。振荡周期约为3秒；振荡的峰-峰值幅度高达平均肌节长度的30%。在单个肌原纤维中偶尔能观察到肌节振荡沿肌原纤维长轴的传播，而在肌原纤维束中则经常能观察到。在ATP存在且Ca2+不存在的情况下，显示肌原纤维发生收缩、振荡或松弛时ADP和Pi浓度范围的“状态”图表明，振荡是骨骼肌介于收缩状态和松弛状态之间的第三种状态。
