Limitations to oxygen diffusion and equilibration in in vitro cell exposure systems in hyperoxia and hypoxia

Exposure of cultured cells to changing gaseous environments is used as a model for understanding both the immediate and long-term effects of such exposures on lung cells in vivo. We conducted experiments with polystyrene tissue culture flasks and plates to determine the time course of changes in oxygen concentration occurring under in vitro conditions. Only a few minutes were required for the concentration of oxygen in the environmental chamber to reach equilibrium with that of the flushing gas. However, >3 h were required for the oxygen content in the medium in the tissue culture flasks and plates to achieve equilibrium. The low solubility of oxygen in aqueous solutions and the limited diffusion of oxygen through a boundary layer of gas above the medium are the major barriers to rapid oxygen transport into the culture medium. The delay in achieving the desired Po-2 within the culture medium limits the temporal precision of any assessment of the correlation of cellular events with the concentration of oxygen to which those cells are exposed.