The levels and kinetics of oxygen tension detectable at the surface of human dermal fibroblast cultures

Low oxygen tension has recently been shown to stimulate cell growth and clo nal expansion, as well as synthesis and transcription of certain growth fac tors and extracellular matrix components. These results have been obtained by exposing cell cultures to a hypoxic environment. Using an oxygen probe, we have now studied how experimental conditions affect the oxygen tension d etectable at the cell surface. Dissolved oxygen tension was directly relate d to the height of the medium above the cell surface (r = 0.8793, P = 0.021 ), but was constant when no cells were present in the flask (r = -0.9732, P = 0.001). In both human dermal fibroblasts and NIH/3T3 cultures, oxygen te nsion decreased linearly as cell density increased (r = -0.835, P < 0.0001; r = -0.916, P < 0.0001, respectively). When human dermal fibroblasts were exposed to 2% O-2, maximum hypoxic levels (0 mmHg) were achieved within app roximately 15 min, and the recovery time was within a similar time frame. T he addition of rotenone, an inhibitor of cellular respiration, blocked this decrease in oxygen tension at the cell surface, suggesting that cellular c onsumption of oxygen is responsible for the decline. Finally, we examined t he cell-surface oxygen tension in control and acutely wounded human skin eq uivalents (HSE), consisting of a keratinocyte layer over a type I collagen matrix containing fibroblasts. We found that oxygen tension dropped signifi cantly (P < 0.0001) in acutely wounded areas of HSE as compared to unwounde d areas of HSE and that this drop was prevented by the addition of mitomyci n C. These results indicate that cell-surface oxygen tension is indirectly related to cell density, and that the amount of detectable oxygen at the ce ll surface is a function of cell density, the oxygen tension in the incubat or, and increased cellular activity, as occurs after injury. (C) 2000 Wiley -Liss, Inc.