Oxygen-independent production of Epo by P19 cells. P19 cells and Hep3B cells were cultured in 21% and 2% oxygen for 24 hours. Epo concentration in the spent medium and the total cellular proteins were determined. Epo production is given as Epo (in picograms) per milligram of cellular protein. Inducibility (2% oxygen/21% oxygen) is indicated. Each value is the mean ± SD of triplicate experiments.