Ranatunga K W
Department of Physiology, School of Medical Sciences, University of Bristol, England.
Biophys J. 1996 Oct;71(4):1905-13. doi: 10.1016/S0006-3495(96)79389-X.
Isometric tension responses to rapid temperature jumps (T-jumps) of 3-7 degrees C were examined in single skinned fibers isolated from rabbit psoas (fast) and soleus (slow) muscles. T-jumps were induced by an infrared laser pulse (wavelength 1.32 microns, pulse duration 0.2 ms) obtained from a Nd-YAG laser, which heated the fiber and bathing buffer solution in a 50-microliter trough. After a T-jump, the temperature near the fiber remained constant for approximately 0.5 s, and the temperature could be clamped for longer periods by means of Peltier units assembled on the back trough wall. A T-jump produced a step decrease in tension in both fast and slow muscle fibers in rigor, indicating thermal expansion. In maximally Ca-activated (pCa approximately 4) fibers, the increase of steady tension with heating (3-35 degrees C) was approximately sigmoidal, and a T-jump at any temperature induced a more complex tension transient than in rigor fibers. An initial (small amplitude) step decrease in tension followed by a rapid recovery (tau(1); see Davis and Harrington, 1993) was seen in some records from both fiber types, which presumably was an indirect consequence of thermal expansion. The net rise in tension after a T-jump was biexponential, and its time course was characteristically different in the two fibers. At approximately 12 degrees C the reciprocal time constants for the two exponential components (tau(2) and tau(3), respectively, were approximately 70.s(-1) and approximately 15.s(-1) in fast fibers and approximately 20.s(-1) and approximately 3.s(-1) in slow fibers. In both fibers, tau(2) ("endothermic force regeneration") became faster with an increase in temperature. Furthermore, tau(3) was temperature sensitive in slow fibers but not in fast fibers. The results are compared and contrasted with previous findings from T-jump experiments on fast fibers. It is observed that the fast/slow fiber difference in the rate of endothermic force generation (three- to fourfold) is considerably smaller than the reported differences in the "phosphate release steps" (> 30-fold).
在从兔腰大肌（快肌）和比目鱼肌（慢肌）分离出的单根去表皮纤维中，检测了等长张力对3至7摄氏度快速温度跃升（T跃变）的反应。T跃变由从Nd-YAG激光获得的红外激光脉冲（波长1.32微米，脉冲持续时间0.2毫秒）诱导产生，该激光脉冲使50微升槽中的纤维和浴液升温。T跃变后，纤维附近的温度在约0.5秒内保持恒定，并且可以通过安装在槽后壁上的珀耳帖装置将温度保持更长时间。T跃变使处于强直状态的快肌和慢肌纤维的张力均出现阶跃下降，表明热膨胀。在最大钙激活（pCa约为4）的纤维中，随着加热（3至35摄氏度），稳定张力的增加近似呈S形，并且在任何温度下的T跃变都会诱导出比强直纤维中更复杂的张力瞬变。在两种纤维类型的一些记录中都观察到，张力先出现初始（小幅度）阶跃下降，随后快速恢复（时间常数tau(1)；见Davis和Harrington，1993），这可能是热膨胀的间接结果。T跃变后张力的净上升是双指数的，并且其时间进程在两种纤维中具有显著差异。在约12摄氏度时，两个指数成分的倒数时间常数（分别为tau(2)和tau(3)）在快肌纤维中约为70.s(-1)和约15.s(-1)，在慢肌纤维中约为20.s(-1)和约3.s(-1)。在两种纤维中，tau(2)（“吸热性力量再生”）都随着温度升高而变快。此外，tau(3)在慢肌纤维中对温度敏感，而在快肌纤维中则不敏感。将这些结果与先前对快肌纤维进行的T跃变实验结果进行了比较和对比。可以观察到，吸热性力量产生速率的快肌/慢肌纤维差异（三到四倍）远小于报道的“磷酸盐释放步骤”差异（>30倍）。
