EPO secretion cells in response to variation of the diffusion distance. Human hepatoma cells (HepG2) were cultured in 24-well polystyrene dishes. When the cells approached confluence the growth medium was replaced with 0.5 mL (which corresponds to a diffusion distance of 2.5 mm) or 1 mL (diffusion distance 5 mm). The experiment was done in the absence or presence of rotenone (1 μM). EPO concentrations determined by ELISA were corrected for medium volume and are therefore given as secreted units. Bars represent mean of 3 independent cultures + SD, without rotenone (□) or with rotenone (▪). Inductions of EPO secretion by hypoxia, by an increase of the diffusion distance and by combination of both, were all statistically significant (P < .05) as calculated by the Dunnett post hoc test.