A study on the dynamics of intracellular calcium ion in myocardium of isolated, perfused hearts during ischemia and after reperfusion.

本课题旨在研究缺血或再灌注心肌的兴奋-收缩耦合，特别是细胞内自由离子Ca^<2+>的动态变化。采用氟核磁共振波谱（^<19>F-NMR）联用Ca^<2+>螯合剂5F-BAPTA，在离体灌注全心细胞内测定激活剂Ca^<2+> ([Ca^<2+>]_i)的细胞内浓度。从它们的F-NMR谱信号中得到心肌中Ca^<2+>结合和Ca^<2+>游离5F-BAPTA的数量，并通过它们的比值确定[Ca^<2+>]_i。在该项目中获得了以下结果：观察缺血和再灌注后[Ca^<2+>]_i的变化。37 C全缺血10 min后细胞内Ca^<2+>浓度较对照组显著升高，但缺血15 min后细胞内Ca^<2+>浓度迅速恢复到对照组水平。我们还关注了“休克心肌”的病理生理学，即心肌在短暂缺血后再灌注。这种短暂的缺血不足以造成坏死，但会造成长时间的收缩功能衰竭。全心缺血15分钟后再灌注的心脏压力在37ºC时显示，即使心脏负荷5F-BAPTA，也只有70%的对照（休克心肌）。与缺血前相比，休克心肌钙转运的幅度（即[Ca^<2+>]_i的周期性变化）明显增加。结合我们之前的研究，这些结果揭示了这种收缩功能障碍是由于肌纤维中Ca^<2+>-最大激活力的降低和肌纤维Ca^<2+>-敏感性的转移，钙瞬态振幅的矛盾增加。

This project aimed on the study of excitation-contraction coupling, especially dynamics of Intracellular free ion Ca^<2+>, in myocardium of ischemlc or reperfused hearts. The intracellular concentration of activator Ca^<2+> ([Ca^<2+>]_i) was measured in Isolated, perfused whole heart using fluorine nuclear magnetic resonance spectroscopy (^<19>F-NMR) coupled with Ca^<2+> chelator, 5F-BAPTA. The amounts of Ca^<2+> bounded and Ca^<2+> free 5F-BAPTA in myocardium were obtained from the signals of them in F-NMR spectrum, and [Ca^<2+>]_i was determined by the ratio of them. The following results were obtained in this project.1. The changes in [Ca^<2+>]_i during ischemia and after reperfusion were investigated. The intracellular Ca^<2+> concentration significantly increased after 10 minutes of global ischemia at 37ﾟC compared with control, but rapidly came back to the control level during early phase of reperfusion after 15 minutes of ischemia.2. We also focused on the pathophysiology of "stunned myocardium", i.e., myocardium reperfused after a brief period of ischemia. Such a brief ischemia is not enough to make necrosis but produces prolonged contractile failure. Developed pressure in the hearts reperfused after 15 minute of global ischemia at 37ﾟC showed only 70% of control (stunned myocardium) even the hearts were loaded with 5F-BAPTA. The amplitude of calcium translent, i.e., cyclical changes in [Ca^<2+>]_i, was significantly increased in stunned myocardium compared with that before ischemia. Coupled with our previous study, theses results revealed that this contractile dysfunction is due to the decrease in maximal Ca^<2+>-activated force in myofildment and the shift of myofilament Ca^<2+>-sensitivity to higher Ca with paradoxical increase in amplitude of calcium transients.