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 mo del for understanding both the immediate and long-term effects of such expo sures on lung cells in vivo. We conducted experiments with polystyrene tiss ue culture flasks and plates to determine the time course of changes in oxy gen concentration occurring under in vitro conditions. Only a few minutes w ere required for the concentration of oxygen in the environmental chamber t o reach equilibrium with that of the flushing gas. However, >3 h were requi red for the oxygen content in the medium in the tissue culture flasks and p lates to achieve equilibrium. The low solubility of oxygen in aqueous solut ions and the limited diffusion of oxygen through a boundary layer of gas ab ove the medium are the major barriers to rapid oxygen transport into the cu lture medium. The delay in achieving the desired Po-2 within the culture me dium limits the temporal precision of any assessment of the correlation of cellular events with the concentration of oxygen to which those cells are e xposed.