Study of energy metabolism-function coupling in cardiac myocyte

1.通过测定豚鼠心室肌细胞膜电位、线粒体NADH荧光和细胞缩短率，探讨能量代谢与心功能的耦合机制。当刺激频率逐步增加时，细胞内的NADH荧光先降低后升高，细胞缩短逐渐增加。在返回到对照刺激频率时，NADH信号在下降到对照水平之前显示出过冲。线粒体Ca^<2+>单向转运体的阻断剂Ru 360或钌红减弱了高速率刺激过程中NADH荧光的增加。用Rhod-2测量的线粒体Ca^<2+>在高速率刺激期间以与NADH荧光类似的时间过程增加。双相启动时间过程可以很好地解释为叠加在ADP反馈控制上的线粒体脱氢的延迟的Ca^<2+>激活，而延迟的脱氢失活时间过程可以很好地解释为抵消时间过程。用大鼠和小鼠心室细胞获得了基本相同的结果。因此，该机制可能是哺乳动物心室细胞的共同机制。2.我们建立了一个包含线粒体氧化磷酸化的心肌细胞兴奋-收缩偶联计算机模型。在Ca^<2+>激活底物脱氢的假设下，计算机模拟很好地再现了NADH的响应。该模型模拟预测，底物脱氢的活化提供了ATP合成的驱动力的约23%，其余的约77%由反馈控制提供。

1.To study mechanisms underlying the coupling between energy metabolism and cardiac function, we measured membrane potential and mitochondrial NADH fluorescence, simultaneously with cell shortening in isolated guinea-pig ventricular myocytes. When a step increase in stimulus frequency was applied, the NADH fluorescence first decreased and then increased to a steady level, while the cell shortening was gradually augmented. Upon returning to the control stimulus frequency, the NADH signal showed an overshoot before declining to the control level. Blockers of mitochondrial Ca^<2+> uniporter, Ru360 or ruthenium red, attenuated the increase of NADH fluorescence during the high rate stimulation. Mitochondrial Ca^<2+>, measured with Rhod-2,increased with a similar time course to that of the NADH fluorescence during the high rate stimulation. The biphasic onset time course was well explained by the delayed Ca^<2+> activation of the mitochondrial dehydrogenation superimposed on the feedback control by ADP, while the offset time course with a delayed deactivation of dehydrogenation. Essentially the same results were obtained with rat and mice ventricular cells. Therefore, the suggested mechanism is probably a common mechanism of mammalian ventricular cells.2.We developed a cardiac cell computer model of excitation-contraction coupling incorporating a mitochondrial oxidative phosphorylation. The computer simulation, on the assumption of Ca^<2+> activation of substrate dehydrogenation, well reconstructed the response of NADH. This model simulation predicted that the activation of substrate dehydrogenation provides 〜23% of driving force of the ATP synthesis, and remaining 〜77% is supplied by the feedback control.