Direct observation of radial intracellular Po2 gradients in a single cardiomyocyte of the rat

The purpose of the present study was to directly visualize radial gradients of intracellular PO2 in a single individual cardiomyocyte isolated from the rat ventricle. Microspectrophotometry with the use of cytosolic myoglobin as an oxygen probe was conducted at 410 nm. When the quiescent cell was incubated with 1 mu M carbonyl cyanide m-chlorophenylhydrazone to increase oxygen consumption approximately eightfold, gradual decreases in myoglobin oxygen saturation (S-Mb) were demonstrated toward the core of the cell, whereas these decreases disappeared when the cell was treated with 2 mM NaCN. These results highlighted the importance of diffusional oxygen transport in determining intracellular oxygenation in cardiac cells. From the measured S-Mb, we assessed the profile of radial changes in intracellular PO2 at the mean S-Mb comparable to that in vivo (similar to 0.5). Quite steep PO2 gradients were demonstrated in the vicinity of the sarcolemma that were rapidly attenuated toward the cell core. These radial profiles of intracellular PO2 demonstrate the significance of myoglobin-facilitated diffusion of oxygen. Furthermore, the shallow gradients of PO2 near the center of the cell might arise from partial depression of oxygen consumption near the cell core.