A study on the excitation-contraction coupling of myocardium - Analysis on isolated, perfused hearts using multi-nuclear NMR methods.

本课题旨在研究体外灌流心脏的兴奋-收缩(E-C)偶联作用。(1)E-C偶联终点评价方法的建立：采用氟核磁共振技术结合5F-BAPTA，测定心肌细胞内激活剂[Ca^&lt；2&gt；]_i浓度。钙瞬变可以通过这种带门控的F-核磁共振技术来评估。最大钙激活压(MCAP)是肌丝最大钙激活力的指标，用兰诺定快速起搏引起的强直状态下的左心室等容压来评价。(2)缺血早期收缩功能衰竭的机制：无机磷(PI)降低MCAP，质子(H^)引起MCAP降低和钙敏感性…移位。更多的是更高的钙。因此，这些结果表明，缺血时PI和H^的增加导致了早期的收缩失效。(3)顿抑心肌的病理生理学：短暂缺血后再灌流可导致无坏死的长时间收缩衰竭(“顿抑心肌”)。顿抑心肌与对照组相比，MCAP降低，钙瞬变幅度增大。因此，这些结果表明，这种收缩功能障碍是由于最大钙激活力的降低和钙敏感性对高钙的移位，并伴随着钙瞬变幅度的反常增加。(4)顿抑心肌的发病机制：我们的研究结果提示，缺血再灌流过程中短暂的钙超载导致顿抑心肌的收缩衰竭。并直接测定缺血及再灌流后[Ca~(2+)]_i的变化，证实钙超载的存在。(5)非缺血性钙超载对心肌收缩功能的影响：阿霉素使心肌细胞[Ca~(2+)]_i升高，但无缺血性改变，导致心肌收缩功能紊乱。因此，这些结果表明，钙超载本身就会恶化心脏功能。较少

This project aimed on the assessment of excitation-contraction (E-C) coupling in myocardium of isolated, perfused hearts.The following results were obtained in this University-to-University Cooperative Research. (1)Development of the methods to assess the endpoints in E-C coupling: The intracellular concentration of activator Ca^<2+> ([Ca^<2+>]_i) was measured in perfused heart using fluorine nuclear magnetic resonance spectroscopy (^<19>F-NMR) coupled with Ca^<2+> chelator, 5F-BAPTA. Calcium transients could be evaluated by this F-NMR technique with gating. Maximal Ca^<2+>-activated pressure (MCAP), the index of maximal Ca^<2+>-activated force in myofilament was evaluated by left ventricular isovolumic pressure during tetani elicited by the rapid pacing after exposure to ryanodine. (2)Mechanism of early contractile failure during ischemia: It was revealed that inorganic phosphate (Pi) decreases MCAP and proton (H^+) induces both the decrease in MCAP and the shift of Ca^<2+>-sensitivit … More y to higher Ca. Thus, these results indicate that the increase of Pi and H^+ during ischemia causes early contractile failure. (3)Pathophysiology of stunned myocardium: Reperfusion after a brief period of ischemia produces prolonged contractile failure without necrosis ("stunned myocardium"). In stunned myocardium, MCAP decreased and the amplitude of calcium transient increased compared with the control. Thus, these results indicate that this contractile dysfunction is due to the decrease in maximal Ca^<2+>-activated force and the shift of Ca^<2+>-sensitivity to higher Ca with paradoxical increase in amplitude of calcium transients. (4)Pathogenesis of stunned myocardium: Our data suggested that a transient calcium overload during ischemia and reperfusion causes the contractile failure in stunned myocardium. The changes in [Ca^<2+>]_i during ischemia and after reperfusion were also directly measured and the exist of calcium overload was confirmed. (5)Effect of non-ischemic calcium overload on contractility: Doxorubicin increased [Ca^<2+>]_i without ischemic changes and caused contractile disorder. Thus, these results indicate that calcium overload itself deteriorates the cardiac function. Less