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首页> 外文期刊>Journal of Muscle Research and Cell Motility >Cardiac titin: molecular basis of elasticity and cellular contribution to elastic and viscous stiffness components in myocardium.
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Cardiac titin: molecular basis of elasticity and cellular contribution to elastic and viscous stiffness components in myocardium.

机译：心脏纤溶蛋白：弹性的分子基础，以及细胞对心肌弹性和粘性刚度成分的贡献。

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Myocardium resists the inflow of blood during diastole through stretch-dependent generation of passive tension. Earlier we proposed that this tension is mainly due to collagen stiffness at degrees of stretch corresponding to sarcomere lengths (SLS) > or = 2.2 microns, but at shorter lengths, is principally determined by the giant sarcomere protein titin. Myocardial passive force consists of stretch-velocity-sensitive (viscous/viscoelastic) and velocity-insensitive (elastic) components; these force components are seen also in isolated cardiac myofibrils or skinned cells devoid of collagen. Here we examine the cellular/myofibrillar origins of passive force and describe the contribution of titin, or interactions involving titin, to individual passive-force components. We construct force-extension relationships for the four distinct elastic regions of cardiac titin, using results of in situ titin segment-extension studies and force measurements on isolated cardiac myofibrils. Then, we compare these relationships with those calculated for each region with the wormlike-chain (WLC) model of entropic polymer elasticity. Parameters used in the WLC calculations were determined experimentally by single-molecule atomic force-microscopy measurements on engineered titin domains. The WLC modelling faithfully predicts the steady-state-force vs. extension behavior of all cardiac-titin segments over much of the physiological SL range. Thus, the elastic-force component of cardiac myofibrils can be described in terms of the entropic-spring properties of titin segments. In contrast, entropic elasticity cannot account for the passive-force decay of cardiac myofibrils following quick stretch (stress relaxation). Instead, slower (viscoelastic) components of stress relaxation could be simulated by using a Monte-Carlo approach, in which unfolding of a few immunoglobulin domains per titin molecule explains the force decay. Fast components of stress relaxation (viscous drag) result mainly from interaction between actin and titin filaments; actin extraction of cardiac sarcomeres by gelsolin immediately suppressed the quickly decaying force transients. The combined results reveal the sources of velocity sensitive and insensitive force components of cardiomyofibrils stretched in diastole.
机译：心肌通过舒张相关的被动张力产生来抵抗舒张期的血液流入。早些时候，我们提出这种张力主要是由于胶原蛋白在与肌节长度（SLS）>或= 2.2微米相对应的拉伸度下的刚度所致，但在较短的长度上，主要由巨肌节蛋白滴定蛋白决定。心肌的被动力由拉伸速度敏感（粘/粘弹性）和速度不敏感（弹性）组成。在分离的心脏肌原纤维或不含胶原的皮肤细胞中也可以看到这些作用力。在这里，我们检查了被动力的细胞/肌原纤维的起源，并描述了titin或涉及titin的相互作用对各个被动力成分的贡献。我们使用原位titin片段延伸研究结果和离体心肌肌原纤维的力测量结果，构建了心脏titin四个不同弹性区域的力-延伸关系。然后，我们使用熵聚合物弹性的蠕虫链（WLC）模型，将这些关系与为每个区域计算的关系进行比较。 WLC计算中使用的参数是通过对工程化的titin域进行单分子原子力显微镜测量实验确定的。 WLC模型忠实地预测了在大部分生理性SL范围内所有心脏-titin段的稳态力与伸展行为。因此，可以根据肌动蛋白片段的熵弹簧特性来描述心肌肌原纤维的弹性成分。相反，熵弹性不能解释快速拉伸（应力松弛）后心肌肌原纤维的被动力衰减。取而代之的是，应力松弛的较慢（粘弹性）分量可以通过使用蒙特卡洛方法进行模拟，其中每个titin分子的几个免疫球蛋白结构域的展开说明了力的衰减。应力松弛（粘性阻力）的快速成分主要来自肌动蛋白和肌动蛋白丝之间的相互作用。凝溶胶蛋白对心肌肉瘤的肌动蛋白提取立即抑制了快速衰减的力瞬变。综合结果揭示了舒张期心肌原纤维的速度敏感和不敏感作用力的来源。

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