Buschman H P, Elzinga G, Woledge R C
Institute of Human Performance, Royal National Orthopaedic Hospital Trust, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
Pflugers Arch. 1996 Nov-Dec;433(1-2):153-9. doi: 10.1007/s004240050261.
We investigated the effect of shortening velocity on the efficiency of single intact slow-twitch muscle fibres (type 3) of Xenopus laevis, at different levels of activation (10, 15, 20 and 40 Hz). Fused contractions were obtained at 40 Hz stimulation. When maximal isometric force had been reached, the fibres were shortened by 10% of the fibre length (L0) at 0.4, 1 and 2 L0/s. To investigate whether the oscillating force at low stimulation frequencies influenced power output and the rate of heat production, we also performed these experiments with the fibre bathed in dantrolene. The results with fused contractions in the presence of dantrolene were the same as with unfused contractions. At 40 Hz stimulation during shortening the rate of heat production increased above that measured during isometric contractions, while at the lower stimulation frequencies the rate of heat production was less than that during isometric contractions. Mechanical efficiency was highest at low activation, and increased more with shortening velocity than at high activation. The actomyosin efficiency (i.e. the efficiency corrected for "activation heat") was also highest at 10 Hz stimulation. We conclude that in slow-twitch muscle fibres of X. laevis, near the optimum shortening velocity, cross-bridge efficiency is highest for partially activated muscle.
我们研究了在不同激活水平（10、15、20和40Hz）下，缩短速度对非洲爪蟾单个完整慢肌纤维（3型）效率的影响。在40Hz刺激下获得了强直收缩。当达到最大等长力时，纤维以0.4、1和2L0/s的速度缩短其长度的10%（L0）。为了研究低刺激频率下的振荡力是否会影响功率输出和产热速率，我们还在纤维浸泡在丹曲林的情况下进行了这些实验。丹曲林存在时强直收缩的结果与非强直收缩的结果相同。在40Hz刺激下缩短过程中，产热速率高于等长收缩时测得的速率，而在较低刺激频率下，产热速率低于等长收缩时的速率。机械效率在低激活时最高，并且随着缩短速度的增加比在高激活时增加得更多。肌动球蛋白效率（即校正了“激活热”的效率）在10Hz刺激时也最高。我们得出结论，在非洲爪蟾的慢肌纤维中，接近最佳缩短速度时，部分激活的肌肉的横桥效率最高。
