Gulati J, Babu A
Science. 1982 Feb 26;215(4536):1109-12. doi: 10.1126/science.6977845.
Contraction of isolated, intact frog muscle fibers under increasing tonicity of the external solution was studied by adding (i) effectively impermeant sodium chloride and sucrose and (ii) permeant potassium chloride. Force of isometric contraction decreased as a function of tonicity, independent of the permeability of the solute. In contrast, cell volume changed with tonicity in impermeant solutes and was constant with potassium chloride. The results are evidence that ionic strength in the sarcoplasm directly influences the contraction mechanism. Also, the findings show that force development is unaffected by changes in fiber volume, suggesting that the force per cross-bridge is constant at different distances between the thin and myofilaments. Finally, in light of the length-force relation, the results support the idea that cross-bridges are independent force generators.
通过添加（i）有效的非渗透性氯化钠和蔗糖以及（ii）渗透性氯化钾，研究了在外部溶液张力增加的情况下分离的完整青蛙肌肉纤维的收缩情况。等长收缩力随张力的增加而降低，与溶质的渗透性无关。相比之下，非渗透性溶质中的细胞体积随张力变化，而氯化钾中的细胞体积保持恒定。结果表明肌浆中的离子强度直接影响收缩机制。此外，研究结果表明力的产生不受纤维体积变化的影响，这表明在细肌丝和粗肌丝之间不同距离处每个横桥的力是恒定的。最后，根据长度-力关系，结果支持横桥是独立力产生器的观点。
