Ranatunga K W
Department of Physiology, Medical School, University of Bristol, United Kingdom.
Biophys J. 1994 May;66(5):1531-41. doi: 10.1016/S0006-3495(94)80944-0.
Temperature dependence of the isometric tension was examined in chemically skinned, glycerinated, rabbit Psoas, muscle fibers immersed in relaxing solution (pH approximately 7.1 at 20 degrees C, pCa approximately 8, ionic strength 200 mM); the average rate of heating/cooling was 0.5-1 degree C/s. The resting tension increased reversibly with temperature (5-42 degrees C); the tension increase was slight in warming to approximately 25 degrees C (a linear thermal contraction, -alpha, of approximately 0.1%/degree C) but became more pronounced above approximately 30 degrees C (similar behavior was seen in intact rat muscle fibers). The extra tension rise at the high temperatures was depressed in acidic pH and in the presence of 10 mM inorganic phosphate; it was absent in rigor fibers in which the tension decreased with heating (a linear thermal expansion, alpha, of approximately 4 x 10(-5)/degree C). Below approximately 20 degrees C, the tension response after a approximately 1% length increase (complete < 0.5 ms) consisted of a fast decay (approximately 150.s-1 at 20 degrees C) and a slow decay (approximately 10.s-1) of tension. The rate of fast decay increased with temperature (Q10 approximately 2.4); at 35-40 degrees C, it was approximately 800.s-1, and it was followed by a delayed tension rise (stretch-activation) at 30-40.s-1. The linear rise of passive tension in warming to approximately 25 degrees C may be due to increase of thermal stress in titin (connectin)-myosin composite filament, whereas the extra tension above approximately 30 degrees C may arise from cycling cross-bridges; based on previous findings from regulated actomyosin in solution (Fuchs, 1975), it is suggested that heating reversibly inactivates the troponin-tropomyosin control mechanism and leads to Ca-independent thin filament activation at high temperatures. Additionally, we propose that the heating-induced increase of endo-sarcomeric stress within titin-myosin composite filament makes the cross-bridge mechanism stretch-sensitive at high temperatures.
在化学去膜、甘油处理的兔腰大肌肌纤维中，研究了等长张力的温度依赖性，这些肌纤维浸浴在松弛溶液中（20℃时pH约为7.1，pCa约为8，离子强度200 mM）；平均加热/冷却速率为0.5 - 1℃/秒。静息张力随温度（5 - 42℃）可逆性增加；升温至约25℃时张力增加轻微（线性热收缩，-α，约为0.1%/℃），但在约30℃以上变得更加明显（完整大鼠肌纤维中也观察到类似行为）。高温下额外的张力升高在酸性pH和存在10 mM无机磷酸盐时受到抑制；在强直纤维中不存在这种情况，强直纤维中的张力随加热而降低（线性热膨胀，α，约为4×10⁻⁵/℃）。在约20℃以下，长度增加约1%（完成时间<0.5毫秒）后的张力响应包括张力的快速衰减（20℃时约为150·s⁻¹）和缓慢衰减（约10·s⁻¹）。快速衰减速率随温度增加（Q10约为2.4）；在35 - 40℃时，约为800·s⁻¹，随后在30 - 40·s⁻¹出现延迟的张力升高（拉伸激活）。升温至约25℃时被动张力的线性升高可能是由于肌联蛋白（连接蛋白） - 肌球蛋白复合丝中热应力的增加，而约30℃以上的额外张力可能源于循环横桥；基于先前溶液中调节性肌动球蛋白的研究结果（Fuchs，1975），提示加热可逆性地使肌钙蛋白 - 原肌球蛋白控制机制失活，并导致高温下与钙无关的细肌丝激活。此外，我们提出加热诱导的肌联蛋白 - 肌球蛋白复合丝内肌节内应力增加使横桥机制在高温下对拉伸敏感。
