Johnston I A, Gleeson T T
Am J Physiol. 1987 Feb;252(2 Pt 2):R371-5. doi: 10.1152/ajpregu.1987.252.2.R371.
Single fast fibers were isolated from the iliofibularis muscles of three species of toad with different thermal minima for active locomotion: 8 degrees C, American toad, Bufo americanus; 15 degrees C, Rocky Mountain toad, Bufo woodhousei woodhousei; 22 degrees C, Cane toad, Bufo marinus. All experiments were carried out during the summer. Fibers were chemically skinned and maximum isometric tension and unloaded contraction velocity were determined at a series of temperatures between 0 and 35 degrees C. At 25-30 degrees C, isometric tension development has a low temperature dependence (R10 = 1.1-1.3) and is in the range of 210-260 kN X m-2 for each of the three toads. However, at 0-10 degrees C, absolute values of tension increase in the series (B. americanus greater than B. woodhousei greater than B. marinus; i.e., with increasing cold tolerance), while thermal sensitivity between 0 and 10 degrees C is inversely related to cold tolerance. For example, at 0 degree C, maximum isometric tension (Po) for the most northerly distributed species is three times higher than for the subtropical to tropical species (P less than 0.001). R10 for Po (0-10 degrees C) is 1.7 for B. marinus, 1.3 for B. w. woodhousei, and 1.0 for B. americanus. In contrast, unloaded shortening speeds were similar at any given temperature for the three species. It is concluded that adaptations in Bufo myosin for activity at low temperatures largely involves changes in force production.
8摄氏度，美洲蟾蜍，美洲蟾蜍；15摄氏度，落基山蟾蜍，伍德豪斯蟾蜍；22摄氏度，蔗蟾蜍，海蟾蜍。所有实验均在夏季进行。对纤维进行化学去皮处理，并在0至35摄氏度的一系列温度下测定最大等长张力和无负荷收缩速度。在25至30摄氏度时，等长张力的产生对温度的依赖性较低（R10 = 1.1 - 1.3），并且三种蟾蜍的等长张力均在210 - 260 kN·m⁻²范围内。然而，在0至10摄氏度时，张力的绝对值在该系列中增加（美洲蟾蜍大于伍德豪斯蟾蜍大于海蟾蜍；即随着耐寒性的增加），而0至10摄氏度之间的热敏感性与耐寒性呈负相关。例如，在0摄氏度时，分布最靠北的物种的最大等长张力（Po）比亚热带至热带物种高两倍（P < 0.001）。Po（0至10摄氏度）的R10对于海蟾蜍为1.7，对于伍德豪斯蟾蜍为1.3，对于美洲蟾蜍为1.0。相比之下，三种物种在任何给定温度下的无负荷缩短速度相似。结论是，蟾蜍肌球蛋白在低温下的活性适应主要涉及力产生的变化。
