Gulati J, Podolsky R J
J Gen Physiol. 1978 Nov;72(5):701-15. doi: 10.1085/jgp.72.5.701.
Calcium and ionic strength are both known to modify the force developed by skinned frog muscle fibers. To determine how these parameters affect the cross-bridge contraction mechanism, the isotonic velocity transients following step changes in load were studied in solutions in which calcium concentration and ionic strength were varied. Analysis of the motion showed that calcium has no effect on either the null time or the amplitude of the transients. In contrast, the transient amplitude was increased in high ionic strength and was suppressed in low ionic strength. These results are consistent with the idea that calcium affects force in skeletal muscle by modulating the number of force generators in a simple switchlike "on-off" manner and that the steady force at a given calcium level is proportional to cross-bridge number. On the other hand, the effect of ionic strength on force is associated with changes in the kinetic properties of the cross-bridge mechanism.
已知钙和离子强度都会改变去皮青蛙肌肉纤维产生的力。为了确定这些参数如何影响横桥收缩机制，我们在改变了钙浓度和离子强度的溶液中研究了负荷阶跃变化后的等张速度瞬变。对运动的分析表明，钙对瞬变的零时或幅度均无影响。相反，在高离子强度下瞬变幅度增大，而在低离子强度下瞬变幅度受到抑制。这些结果与以下观点一致：钙通过以简单的开关式“开-关”方式调节力产生器的数量来影响骨骼肌中的力，并且在给定钙水平下的稳定力与横桥数量成正比。另一方面，离子强度对力的影响与横桥机制的动力学特性变化有关。
