Adaptation of oxygen transport to cardiac cells in ischemia

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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.