Cell culture has historically been performed at near ambient atmospheric (18–21%) partial pressure of oxygen (pO2). Special instrumentation is needed to maintain physiological levels of oxygen tension. In addition, hypoxia, defined as a lower than normal pO2 at the cell or tissue level, has long been known to be detrimental to cell metabolism and viability.
Culturing cells in ambient atmosphere (21% pO2) insures the cells have “enough” oxygen but most cells experience an in vivo pO2 between 0.7 and 7%. Recent studies have shown that cells grown at 21% pO2 have altered phenotypes and gene-expression levels as compared to cells grown at a more physiologically normoxic level.
Incubators and glove boxes can be set for a relevant physiologic pO2 atmosphere, but because cellular respiration removes O2 from the liquid media (rather than the gaseous atmosphere), the gaseous pO2 level for the incubation is not a good estimation of the pO2 the cells are actually experiencing. Instead, there is a need to measure pO2 at the level of the cellular monolayer, the pericellular pO2, to know the precise oxygen conditions to which the cells are being exposed.