Yasuda K, Shindo Y, Ishiwata S
Advanced Research Laboratory, Saitama, Japan.
Biophys J. 1996 Apr;70(4):1823-9. doi: 10.1016/S0006-3495(96)79747-3.
An isotonic control system for studying dynamic properties of single myofibrils was developed to evaluate the change of sarcomere lengths in glycerinated skeletal myofibrils under conditions of spontaneous oscillatory contraction (SPOC) in the presence of inorganic phosphate and a high ADP-to-ATP ratio. Sarcomere length oscillated spontaneously with a peak-to-peak amplitude of about 0.5 microns under isotonic conditions in which the external loads were maintained constant at values between 1.5 x 10(4) and 3.5 x 10(4) N/m2. The shortening and yielding of sarcomeres occurred in concert, in contrast to the previously reported conditions (isomeric or auxotonic) under which the myofibrillar tension is allowed to oscillate. This synchronous SPOC appears to be at a higher level of synchrony than in the organized state of SPOC previously observed under auxotonic conditions. The period of sarcomere length oscillation did not largely depend on external load. The active tension under SPOC conditions increased as the sarcomere length increased from 2.1 to 3.2 microns, although it was still smaller than the tension under normal Ca2+ contraction (which is on the order of 10(5) N/m2). The synchronous SPOC implies that there is a mechanism for transmitting information between sarcomeres such that the state of activation of sarcomeres is affected by the state of adjacent sarcomeres. We conclude that the change of myofibrillar tension is not responsible for the SPOC of each sarcomere but that it affects the level of synchrony of sarcomere oscillations.
为了评估在无机磷酸盐存在和高ADP与ATP比率条件下，甘油化骨骼肌肌原纤维在自发振荡收缩（SPOC）情况下肌节长度的变化，我们开发了一种用于研究单个肌原纤维动态特性的等张控制系统。在等张条件下，外部负载保持恒定在1.5×10⁴至3.5×10⁴ N/m²之间，肌节长度自发振荡，峰峰值幅度约为0.5微米。与先前报道的允许肌原纤维张力振荡的条件（等长或辅助等张）相反，肌节的缩短和屈服是协同发生的。这种同步的SPOC似乎比先前在辅助等张条件下观察到的有组织状态的SPOC具有更高的同步水平。肌节长度振荡的周期在很大程度上不依赖于外部负载。在SPOC条件下，随着肌节长度从2.1微米增加到3.2微米，主动张力增加，尽管它仍然小于正常Ca²⁺收缩下的张力（约为10⁵ N/m²）。同步的SPOC意味着存在一种在肌节之间传递信息的机制，使得肌节的激活状态受到相邻肌节状态的影响。我们得出结论，肌原纤维张力的变化不是每个肌节SPOC的原因，但它会影响肌节振荡的同步水平。
