De Winkel M E, Blangé T, Treijtel B W
Department of Physiology, University of Amsterdam, The Netherlands.
J Muscle Res Cell Motil. 1994 Apr;15(2):130-44. doi: 10.1007/BF00130424.
The viscoelastic properties of crossbridges in rigor state are studied by means of application of small length changes, completed within 30 microseconds, to isometric skinned fibre segments of the iliofibularis muscle of the frog in relaxed and rigor state and measurement of the tension response. Results are expressed as a complex Young's modulus, the real part of which denotes normalized stiffness, while the imaginary part denotes normalized viscous mechanical impedance. Young's modulus was examined over a wide frequency range varying from 5 Hz up to 50 kHz. Young's modulus can be interpreted in terms of stiffness and viscous friction of the half-sarcomere or in terms of elastic changes in tension and recovery upon a step length change. The viscoelastic properties of half-sarcomeres of muscle fibre segments in rigor state showed strong resemblance to those of activated fibres in that shortening a muscle fibre in rigor state resulted in an immediate drop in tension, after which half of the drop in tension was recovered. The following slower phases of tension recovery--a subsequent drop in tension and slow completion of tension recovery--as seen in the activated state, do not occur in rigor state. The magnitude of Young's moduli of fibres in rigor state generally decreased from a value of 3.12 x 10(7) N m-2 at 40 kHz to 1.61 x 10(7) N m-2 at about 100 Hz. Effects of increased viscosity of the incubation medium, decreased interfilament distance in the relaxed state and variation of rigor tension upon frequency dependence of complex Young's modulus have been investigated. Variation of tension of crossbridges in rigor state influenced to some extent the frequency dependence of the Young's modulus. Recovery in relaxed state is not dependent on the viscosity of the medium. Recovery in rigor is slowed down at raised viscosity of the incubation medium, but less than half the amount expected if viscosity of the medium would be the cause of internal friction of the half-sarcomere. Internal friction of the half-sarcomere in the relaxed fibre at the same interfilament distance as in rigor is different from internal friction in rigor. It will be concluded that time necessary for recovery in rigor cannot be explained by friction due to the incubation medium. Instead, recovery in rigor expressed by the frequency dependence of the Young's modulus has to be due to intrinsic properties of crossbridges. These intrinsic properties can be explained by the occurrence of state transitions of crossbridges in rigor.(ABSTRACT TRUNCATED AT 400 WORDS)
通过对处于松弛和僵直状态的青蛙髂腓肌等长去皮肤纤维段施加在30微秒内完成的小长度变化，并测量张力响应，研究了处于僵直状态的横桥的粘弹性特性。结果以复杨氏模量表示，其实部表示归一化刚度，虚部表示归一化粘性机械阻抗。在5赫兹至50千赫的宽频率范围内研究了杨氏模量。杨氏模量可以用半肌节的刚度和粘性摩擦来解释，也可以用步长变化时张力的弹性变化和恢复来解释。处于僵直状态的肌纤维段半肌节的粘弹性特性与活化纤维的粘弹性特性非常相似，因为在僵直状态下缩短肌纤维会导致张力立即下降，之后张力下降的一半会恢复。在活化状态下看到的随后较慢的张力恢复阶段——随后的张力下降和张力恢复的缓慢完成——在僵直状态下不会发生。处于僵直状态的纤维的杨氏模量大小通常从40千赫时的3.12×10⁷牛·米⁻²下降到约100赫兹时的1.61×10⁷牛·米⁻²。研究了孵育介质粘度增加、松弛状态下丝间距离减小以及僵直张力变化对复杨氏模量频率依赖性的影响。处于僵直状态的横桥张力变化在一定程度上影响了杨氏模量的频率依赖性。松弛状态下的恢复不依赖于介质的粘度。在孵育介质粘度升高时，僵直状态下的恢复会减慢，但如果介质粘度是半肌节内摩擦的原因，减慢的幅度不到预期值的一半。在与僵直状态相同的丝间距离下，松弛纤维中半肌节的内摩擦与僵直状态下的内摩擦不同。可以得出结论，僵直状态下恢复所需的时间不能用孵育介质的摩擦来解释。相反，由杨氏模量频率依赖性表示的僵直状态下的恢复必须归因于横桥的固有特性。这些固有特性可以用僵直状态下横桥状态转变的发生来解释。（摘要截于400字）
