Electron paramagnetic resonance oximetry as a quantitative method to measure cellular respiration: A consideration of oxygen diffusion interference

Electron paramagnetic resonance (EPR) oximetry is being widely used to measure the oxygen consumption of cells, mitochondria, and submitochondrial particles. However, further improvement of this technique, in terms of data analysis, is required to use it as a quantitative tool. Here, we present a new approach for quantitative analysis of cellular respiration using EPR oximetry. The course of oxygen consumption by cells in suspension has been observed to have three distinct zones: pO₂-independent respiration at higher pO₂ ranges, pO₂-dependent respiration at low pO ₂ ranges, and a static equilibrium with no change in pO₂ at very low pO₂ values. The approach here enables one to comprehensively analyze all of the three zones together - where the progression of O₂ diffusion zones around each cell, their overlap within time, and their potential impact on the measured pO₂ data are considered. The obtained results agree with previously established methods such as highresolution respirometry measurements. Additionally, it is also demonstrated how the diffusion limitations can depend on cell density and consumption rate. In conclusion, the new approach establishes a more accurate and meaningful model to evaluate the EPR oximetry data on cellular respiration to quantify related parameters using EPR oximetry.