Visualization of oxygen level inside a single cardiac myocyte.

The present paper describes theoretical and experimental bases for quantitation of the oxygen level inside a single isolated ventricular rat myocyte. We applied three-wavelength microspectrophotometry to a single cardiomyocyte, where the sensitivity of the spectrophotometry was augmented by a digital image processing technique known as video-enhanced microscopy. Oxygen-dependent changes in light absorption of the intracellular pigments were detected and represented with the use of a newly defined variable, Z, where one pixel of the reconstructed cell image corresponded to 0.2 microns. Theoretically, Z is a single-valued function of the fractional oxygen saturation of the intracellular pigment. We demonstrated in quiescent cardiomyocytes that Z changed according to extracellular PO2, where the relationship was sigmoidal with the extracellular PO2 for a half-maximal Z of 3.2 Torr. In the aerobic cell, conversion of cytochromes to the reduced forms by NaCN did not affect Z value. Therefore, we conclude that Z mainly represents the fractional oxygen saturation of myoglobin, thus reporting cytosolic PO2. We also demonstrated that for extracellular PO2 of 1.3 Torr, abolition of mitochondrial oxygen consumption by NaCN significantly elevated the intracellular oxygen level, suggesting existence of oxygen pressure gradients in a quiescent single cardiomyocyte that were proportional to oxygen flux.