Measurements of Intracellular Concentrations of Oxygen: Experimental Results and Conceptual Implications of an Observed Gradient Between Intracellular and Extracellular Concentrations of Oxygen

Abstract

The Intracellular concentration of oxygen ([O2]) is the pertinent parameter for most physiological, pathophysiological, and therapeutic considerations, but it seldom is measured directly. This paradox is explained by a combination of a lack of awareness and a lack of methodology. The literature is quite mixed in regard to the occurrence of significant gradients between the intracellular and extracellular compartments. Everyone agrees, of course, that there must be some gradient because oxygen enters from the outside of the cell and is consumed inside the cell, principally by the mitochondria. The disagreements are in regard to the size of the gradient, with arguments being made on theoretical grounds that there should or should not be a significant gradient. There also are some experimental reports of indirect measures of intracellular oxygen concentrations and these, like the theoretical reports, have quite variable conclusions with reports of both no significant gradients and relatively large gradients (1–11).