Analyses of transmural difference of myocardial crossbridge dynamics using SPring-8 synchrotron facility

容量依赖性增加心脏功能的机制（Frank-Starling定律）是心血管生理学中的一个有趣的主题。Frank-Starling定律的可能机制是肌钙蛋白晶格间距的减小，以及与肌钙蛋白和肌动蛋白肌球蛋白相互作用速率的钙结合亲和力的增加，并具有强结合的交叉桥。然而，心脏具有复杂的三维结构，因此肌丝取向和应变的区域不均匀性可能在调节心脏性能中起重要作用。我们使用SPring-8同步加速器装置揭示了周期性心脏搏动期间跨壁动力学的差异。在收缩期，心外膜和中膜跨桥动力学与左心室压力发展协调良好。而在舒张期，正中横桥的衰减明显早于心外膜横桥。前负荷水平的改变对该区域的运动无明显影响。 关于我们 我们还发现，在高和低预负荷水平下，心外膜区的肌球蛋白晶格间距明显小于中膜区。假设在心肌细胞的伸展和释放期间晶格体积是恒定的，肌球蛋白晶格间距的减小意味着肌节的延长，反之亦然。因此，无论前负荷水平如何，心外膜区的肌节长度都比中膜区长。通常，内膜或更深区域的动作电位持续时间比心外膜区长。目前的结果与这种跨壁电活动的异质性相矛盾。然而，肌节长度越长，抽搐收缩的持续时间越长。因此，长动作电位和短肌节长度的收缩持续时间在正中区域似乎与短动作电位和长肌节长度的收缩持续时间在心外膜区域。(297/300字）减

Mechanism of volume dependent increase in cardiac performance (Frank-Starling law) is interesting theme in the cardiaovascular physiology. Possible mechanisms of the Frank-Starling law are decrease in the myofilamet lattice spacing, and increase in the calcium binding affinity to troponin and actin myosin interaction rate with strongly bound crossbrdge. However the heart has complex three-dimensional structure so the regional heterogeneities of myofilament orientation and strain may have important role in regulation of the cardiac performance.We revealed the transmural difference of crossbridge dynamics using the SPring-8 synchrotron facility during cyclic heart beats. During contraction phase, epicardial and midcardial crossbridge dynamics were harmonized well with the left ventricular pressure development. However during relaxation phase, midcardial crossbridge decayed significantly earlier than epicardial one. The changes of the preload level did not affect on this regional differen … More ce of crossbridge decay.We also found the myosin lattice spacing in the epicardial region was significantly smaller than that in the midcardial region at both high and low preload levels. With an assumption that the lattice volume is constant during stretch and release of the cardiomyocyte, decrease in the myosin lattice spacing means the lengthening of the sarcomere and vice versa. Thus the epicardial region would work with longer sarcomere length than the midcardial region regardless of preload levels.Generally the duration of action potential in the endocardial or deeper region is longer than the epicardial region. The present results contradicts to this transmural heterogeneity of electrical activity. However the longer duration of twitch contraction is observed at the longer sarcomere length. Thus the duration of contraction with the long action potential and short sarcomere length in the midcardial region seemed to be comparable with the duration of contraction with the short action potential and long sarcomere length in the epicardial region. (297/300 words) Less