School of Physiology and Pharmacology, University of Bristol, Bristol, UK.
Biophys J. 2013 Aug 20;105(4):928-40. doi: 10.1016/j.bpj.2013.07.009.
We examined whether cross-bridge cycle models with one or two tension-generating steps can account for the force-velocity relation of and tension response to length steps of frog skeletal muscle. Transition-state theory defined the strain dependence of the rate constants. The filament stiffness was non-Hookean. Models were refined against experimental data by simulated annealing and downhill simplex runs. Models with one tension-generating step were rejected, as they had a low efficiency and fitted the experimental data relatively poorly. The best model with two tension-generating steps (stroke distances 5.6 and 4.6 nm) and a cross-bridge stiffness of 1.7 pN/nm gave a good account of the experimental data. The two tensing steps allow an efficiency of up to 38% during shortening. In an isometric contraction, 54.7% of the attached heads were in a pre-tension-generating state, 44.5% of the attached heads had undergone the first tension-generating step, and only 0.8% had undergone both tension-generating steps; they bore 34%, 64%, and 2%, respectively, of the isometric tension. During slow shortening, the second tensing step made a greater contribution. During lengthening, up to 93% of the attached heads were in a pre-tension-generating state yet bore elevated tension by being dragged to high strains before detaching.
我们研究了具有一个或两个张力产生步骤的交联循环模型是否可以解释蛙类骨骼肌的力-速度关系和张力对长度阶跃的响应。过渡态理论定义了速率常数的应变依赖性。细丝刚度是非胡克的。通过模拟退火和下坡单纯形运行对模型进行了细化，以符合实验数据。由于效率低且对实验数据拟合较差，因此拒绝了具有一个张力产生步骤的模型。具有两个张力产生步骤（冲程距离为 5.6nm 和 4.6nm）和交联刚度为 1.7pN/nm 的最佳模型可以很好地解释实验数据。两个紧张步骤允许在缩短过程中效率高达 38%。在等长收缩中，54.7%的附着头部处于预张力产生状态，44.5%的附着头部经历了第一个张力产生步骤，只有 0.8%的附着头部经历了两个张力产生步骤；它们分别承受 34%、64%和 2%的等长张力。在缓慢缩短期间，第二紧张步骤的贡献更大。在伸长过程中，多达 93%的附着头部处于预张力产生状态，但在分离之前被拖到高应变处以承受升高的张力。
