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兴奋-收缩耦联，特别是细胞内游离Ca^<2+>的动态变化。在离体灌注的整个心脏中，使用氟核磁共振光谱（13 F-NMR）结合Ca^&lt;2 +&gt;螯合剂5 F-BAPTA测量激活剂Ca^&lt;2 +&gt;（[Ca^&lt;2+]_i）的细胞内浓度<19>。根据5 F-BAPTA在F-NMR谱中的信号，计算心肌中结合Ca^&lt;2 +&gt;和游离Ca^&lt;2+&gt;的量，并根据它们的比值确定[Ca^&lt;2+]_i。本项目取得了以下成果：1.观察缺血及再灌注后[Ca^&lt;2+&gt;] i的变化。37 ℃全脑缺血10 min后，细胞内Ca^&lt;2+&gt;浓度较对照组显著升高，但在缺血15 min后再灌注早期迅速恢复至对照组水平.我们还关注了“顿抑心肌”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，但会造成长期的收缩衰竭。在37 ℃下全脑缺血15分钟后再灌注的心脏中，即使心脏负载有5 F-BAPTA，也仅显示出对照（顿抑心肌）的70%。钙电流的幅度，即，顿抑心肌[Ca^&lt;2+&gt;]_i的周期性变化较缺血前显著增加。结合我们以前的研究，这些结果表明，这种收缩功能障碍是由于肌纤维中最大Ca^&lt;2+&gt;激活力的降低和肌丝Ca^&lt;2+&gt;敏感性向高Ca的转移，同时钙瞬变幅度反常地增加。

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.