Foundational Quantum Technology Research Directorate, National Institutes for Quantum Science and Technology , Gunma, Japan.
Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan.
J Gen Physiol. 2023 Dec 4;155(12). doi: 10.1085/jgp.202313414. Epub 2023 Oct 23.
Contraction of striated muscles is initiated by an increase in cytosolic Ca2+ concentration, which is regulated by tropomyosin and troponin acting on actin filaments at the sarcomere level. Namely, Ca2+-binding to troponin C shifts the "on-off" equilibrium of the thin filament state toward the "on" state, promoting actomyosin interaction; likewise, an increase in temperature to within the body temperature range shifts the equilibrium to the on state, even in the absence of Ca2+. Here, we investigated the temperature dependence of sarcomere shortening along isolated fast skeletal myofibrils using optical heating microscopy. Rapid heating (25 to 41.5°C) within 2 s induced reversible sarcomere shortening in relaxing solution. Further, we investigated the temperature-dependence of the sliding velocity of reconstituted fast skeletal or cardiac thin filaments on fast skeletal or β-cardiac myosin in an in vitro motility assay within the body temperature range. We found that (a) with fast skeletal thin filaments on fast skeletal myosin, the temperature dependence was comparable to that obtained for sarcomere shortening in fast skeletal myofibrils (Q10 ∼8), (b) both types of thin filaments started to slide at lower temperatures on fast skeletal myosin than on β-cardiac myosin, and (c) cardiac thin filaments slid at lower temperatures compared with fast skeletal thin filaments on either type of myosin. Therefore, the mammalian striated muscle may be fine-tuned to contract efficiently via complementary regulation of myosin and tropomyosin-troponin within the body temperature range, depending on the physiological demands of various circumstances.
横纹肌的收缩是由细胞浆 Ca2+ 浓度的增加引发的，而 Ca2+ 浓度的增加受肌球蛋白结合蛋白和肌钙蛋白的调节，它们在肌节水平上作用于肌动蛋白丝。具体来说，Ca2+ 与肌钙蛋白 C 的结合使细丝状态的“开-关”平衡向“开”状态移动，促进肌球蛋白与肌动蛋白的相互作用；同样，在体温范围内增加温度也会使平衡向“开”状态移动，即使在没有 Ca2+ 的情况下也是如此。在这里，我们使用光学加热显微镜研究了分离的快速骨骼肌肌原纤维中肌节缩短对温度的依赖性。在 2 秒内快速加热（25 到 41.5°C）可使松弛溶液中的肌节发生可逆缩短。此外，我们在体外运动测定中研究了在体温范围内快速骨骼肌或β-心脏肌球蛋白上再构成的快速骨骼肌或β-心脏细肌丝的滑动速度对温度的依赖性。我们发现：(a) 对于快速骨骼肌细肌丝在快速骨骼肌肌球蛋白上，温度依赖性与快速骨骼肌肌原纤维中肌节缩短的温度依赖性相当（Q10∼8）；(b) 两种类型的细肌丝在快速骨骼肌肌球蛋白上的滑动起始温度均低于在β-心脏肌球蛋白上的起始温度；(c) 与快速骨骼肌细肌丝相比，心脏细肌丝在两种类型的肌球蛋白上的滑动起始温度均较低。因此，哺乳动物横纹肌可能通过在体温范围内对肌球蛋白和肌球蛋白结合蛋白-肌钙蛋白进行互补调节，根据各种情况下的生理需求来精细调节收缩效率。
