Adaptation of oxygen transport to cardiac cells in ischemia

我们已经构建了一个显微分光光度系统，可视化内的一个单独的心肌细胞与高空间分辨率（<1 μ m）的氧分子的分布。使用410 nm-425 nm-445 nm的波长对进行光谱测定，可以评价胞质溶胶中肌红蛋白的氧结合分数（即细胞内氧合）沿着由线粒体引起的光吸收。利用该系统，我们研究了细胞外Po_2、细胞内Po_2与细胞耗氧量之间的关系。当细胞外Po_2降至约7 Torr时，对照细胞胞浆肌红蛋白发生脱氧。相反，当使用氧化磷酸化解偶联剂使细胞的耗氧量加倍时，非常高的细胞外Po_2（28 Torr）不能提供足够的氧供应用于胞内空间的氧合。因此，我们认为细胞内的氧分压高度依赖于细胞的耗氧量，从而表明氧扩散阻力对细胞氧供应有重要影响。我们进一步研究了细胞内氧扩散阻力的意义。细胞内氧分布的直接可视化显示了在呼吸线粒体附近产生的氧压梯度。这一结果可能表明，由线粒体附近的细胞内氧扩散阻力引起的氧压梯度决定了线粒体的氧供应。

We have constructed a microspectrophotometric system that visualizes distribution of oxygen molecule inside a single isolated cardiomyocyte with a high spatial resolution (<1mum). Using a wavelength pair of 410nm-425nm-445nm for spectrometry, it was possible to evaluate fractional oxygen binding of myoglobin in cytosol (i.e.intracellular oxygenation) along with light absorption caused by mitochondria. Using above system, we examined the relationship among extracellular Po_2, intracellular Po_2, and cellular oxygen consumption. Deoxygenation of cytosolic myoglobin occurred in the control cell when extracellular Po_2 was decreased to approximately 7 Torr. In contrast, very high extracellular Po_2 (28 Torr) did not provide oxygen supply enough for oxygenation of intracellular space when oxygen consumption of the cell was doubled by using an uncoupler of oxidative phosphorylation. Therefore, we conclude that intracellular Po_2 is highly dependent of oxygen consumption of the cell, thus indicating significant effect of oxygen diffusion resistance on cellular oxygen supply. We further investigated the significance of intracellular oxygen diffusion resistance. Direct visualization of the distribution of intracellular oxygen demonstrated oxygen pressure gradients produced in the vicinity of respiring mitochondria. This result may indicate that oxygen pressure gradients caused by intracellular oxygen diffusion resistance near mitochondria determine oxygen supply to mitochondria.