History-dependent properties of skeletal muscle myofibrils contracting along the ascending limb of the force-length relationship
History-dependent properties of skeletal muscle myofibrils contracting along the ascending limb of the force-length relationship
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DOI：
10.1098/rspb.2009.1579
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发表时间：
2010-02-07
影响因子：
4.7
通讯作者：
Rassier, Dilson E.
中科院分区：
文献类型：
--
作者：
Pun, Clara;Syed, Ali;Rassier, Dilson E.
骨骼肌收缩存在历史依赖性：拉伸激活的肌肉会导致持久的力量增强，而缩短激活的肌肉会导致持久的力量下降。这些依赖于历史的特性无法用当前的肌肉收缩模型来解释，其机制尚不清楚。本研究的目的是（i）评估短长度（力-长度（FL）关系的升肢）是否存在力增强和力抑制，（ii）评估历史依赖性特性是否与肌节长度（SL）不均匀性相关，以及（iii）确定跨桥（de）激活对力抑制的影响。分离兔腰肌肌原纤维并将其附着在两个微针之间以进行力测量。将肌原纤维的图像投影到线性光电二极管阵列上以测量 SL。肌原纤维被 Ca2+ 或 MgADP 激活；后者独立于 Ca2+ 诱导肌动蛋白的跨桥附着。激活的肌原纤维沿 FL 关系的上升肢进行 3 次拉伸或缩短（在约 0.07 μ m s(-1) 肌节 21 处约 4% SL），由等长收缩周期（约 5 s）分隔。在相似的 SL 下，拉伸后的力高于缩短后的力。力的差异不能用 SL 不均匀性来解释。 Ca2+- 和 MgADP 激活的肌原纤维产生的 FL 关系在拉伸实验中相似，但在缩短后，MgADP 激活产生的力高于 Ca2+ 激活。由于 MgADP 诱导强结合跨桥的形成，该结果表明缩短后的力抑制与跨桥失活相关。
There is a history dependence of skeletal muscle contraction: stretching activated muscles induces a long-lasting force enhancement, while shortening activated muscles induces a long-lasting force depression. These history-dependent properties cannot be explained by the current model of muscle contraction, and its mechanism is unknown. The purposes of this study were (i) to evaluate if force enhancement and force depression are present at short lengths (the ascending limb of the force-length (FL) relationship), (ii) to evaluate if the history-dependent properties are associated with sarcomere length (SL) non-uniformity and (iii) to determine the effects of cross-bridge (de) activation on force depression. Rabbit psoas myofibrils were isolated and attached between two microneedles for force measurements. Images of the myofibrils were projected onto a linear photodiode array for measurements of SL. Myofibrils were activated by either Ca2+ or MgADP; the latter induces cross-bridge attachment to actin independently of Ca2+. Activated myofibrils were subjected to three stretches or shortenings (approx. 4% SL at approx. 0.07 mu m s(-1) sarcomere 21) along the ascending limb of the FL relationship separated by periods (approx. 5 s) of isometric contraction. Force after stretch was higher than force after shortening at similar SLs. The differences in force could not be explained by SL non-uniformity. The FL relationship produced by Ca2+- and MgADP-activated myofibrils were similar in stretch experiments, but after shortening MgADP activation produced forces that were higher than Ca2+ activation. Since MgADP induces the formation of strongly bound cross-bridges, this result suggests that force depression following shortening is associated with cross-bridge deactivation.