Mutungi G, Ranatunga K W
Department of Physiology, School of Medical Sciences, University of Bristol, England.
Biophys J. 1996 Mar;70(3):1432-8. doi: 10.1016/S0006-3495(96)79702-3.
Tension responses to ramp stretches of 1-3% Lo (fiber length) in amplitude were examined in resting muscle fibers of the rat at temperatures ranging from 10 degrees C to 36 degrees C. Experiments were done using bundles of approximately 10 intact fibers isolated from the extensor digitorum longus (a fast muscle) and the soleus (a slow muscle). At low temperatures (below approximately 20 degrees C), the tension response consisted of an initial rise to a peak during the ramp followed by a complex tension decay to a plateau level; the tension decay occurred at approximately constant sarcomere length. The tension decay after a standard stretch at approximately 3-4.Lo/s contained a fast, an intermediate, and a (small amplitude) slow component, which at 10 degrees C (sarcomere length approximately 2.5 microns) were approximately 2000.s-1, approximately 150.s-1, and approximately 25.s-1 for fast fibers and approximately 2000.s-1, approximately 70.s-1 and approximately 8.s-1 for slow fibers, respectively. The fast component may represent the decay of interfilamentary viscous resistance, and the intermediate component may be due to viscoelasticity in the gap (titin, connectin) filament. The two- to threefold fast-slow muscle difference in the rate of passive tension relaxation (in the intermediate and the slow components) compares with previously reported differences in the speed of their active contractions; this suggests that "passive viscoelasticity" is appropriately matched to contraction speed in different muscle fiber types. At approximately 35 degrees C, the fast and intermediate components of tension relaxation were followed by a delayed tension rise at approximately 10.s-1 (fast fibers) and 2.5.s-1 (slow fibers); the delayed tension rise was accompanied by sarcomere shortening. BDM (5-10 mM) reduced the active twitch and tetanic tension responses and the delayed tension rise at 35 degrees C; the results indicate stretch sensitive activation in mammalian sarcomeres at physiological temperatures.
在10摄氏度至36摄氏度的温度范围内，对大鼠静息肌纤维施加幅度为1 - 3% Lo（纤维长度）的斜坡拉伸时的张力反应进行了研究。实验使用从趾长伸肌（一种快肌）和比目鱼肌（一种慢肌）分离出的约10根完整纤维束进行。在低温（约20摄氏度以下）时，张力反应包括在斜坡拉伸期间最初上升至峰值，随后是复杂的张力衰减至平台水平；张力衰减发生在近似恒定的肌节长度。在约3 - 4 Lo/s的标准拉伸后，张力衰减包含一个快速、一个中间和一个（小幅度）慢速成分，在10摄氏度（肌节长度约2.5微米）时，快肌纤维的这三个成分分别约为2000 s-1、约150 s-1和约25 s-1，慢肌纤维的分别约为2000 s-1、约70 s-1和约8 s-1。快速成分可能代表丝间粘性阻力的衰减，中间成分可能归因于间隙（肌联蛋白、连接蛋白）丝中的粘弹性。被动张力松弛速率（在中间和慢速成分中）快肌与慢肌相差两到三倍，这与先前报道的它们主动收缩速度的差异相符；这表明“被动粘弹性”与不同肌纤维类型的收缩速度相匹配。在约35摄氏度时，张力松弛的快速和中间成分之后是延迟的张力上升，快肌纤维约为10 s-1，慢肌纤维约为2.5 s-1；延迟的张力上升伴随着肌节缩短。BDM（5 - 10 mM）降低了35摄氏度时的主动单收缩和强直张力反应以及延迟的张力上升；结果表明在生理温度下哺乳动物肌节中存在拉伸敏感激活。
