Ulbrich M, Rüegg J C
Pflugers Arch. 1976 Jun 22;363(3):219-22. doi: 10.1007/BF00594604.
In glycerol-extracted insect fibrillar muscle suspended in ATP salt solution the incorporation of 32Pi into ATP was studied during the performance of positive or negative oscillatory work and under a variety of mechanical and ionic conditions. An increase in calcium ion concentration from 10(-8)--10(-5) M increased the incorporation rate in proportion to the increase in ATPase activity, mean tension and immediate stiffness, which is a measure of the extent of actin-myosin interaction. Sinusoidal stretches (at 1% Lo) performed at 5 Hz induced the fibres to perform optimal positive oscillatory work and it caused a doubling of the incorporation rate (ant ATPase activity). A decrease or increase of the frequency below or above the optimum of 5 Hz always decreased the power output as well as the incorporation rate which, however, was still noticeable even under conditions where work was done on the fibres. A similar frequency dependence was found when square-wave rather than sinusoidal stretches were applied and this effect could be related to the finding that the rate of stretch-induced incorporation was highest shortly after stretching and then declined to low values (after about 100 ms). These results suggest the formation of an energy-rich intermediate (actomyosin-ADP?) during the contraction process induced by stretching and this intermediate must be assumed to accumulate transiently after stretching.
在悬浮于ATP盐溶液中的甘油提取的昆虫纤维状肌肉中，研究了在进行正向或负向振荡功时以及在各种机械和离子条件下32Pi掺入ATP的情况。钙离子浓度从10(-8) - 10(-5) M增加，掺入速率与ATP酶活性、平均张力和即时硬度的增加成比例，即时硬度是肌动蛋白-肌球蛋白相互作用程度的一种度量。以5 Hz进行的正弦拉伸（在1% Lo）使纤维进行最佳正向振荡功，并使掺入速率（和ATP酶活性）加倍。频率低于或高于最佳值5 Hz时，功率输出以及掺入速率均下降，然而，即使在对纤维做功的条件下，掺入速率仍然很明显。当施加方波而非正弦拉伸时，发现了类似的频率依赖性，这种效应可能与拉伸诱导掺入速率在拉伸后不久最高然后下降到低值（约100毫秒后）这一发现有关。这些结果表明在拉伸诱导的收缩过程中形成了一种富含能量的中间体（肌动球蛋白-ADP？），并且必须假定这种中间体在拉伸后会短暂积累。
