Proliferation of hNPCs. Effects of high and low oxygen concentration on the proliferation of hNPCs. Cells were treated with different EPO concentrations up to 4 d. Number of cells/ml was determined at 20% oxygen (A) and 3% oxygen (B). Comparing untreated cells (C), hypoxia had no impact on the proliferation rate within 4 d. The doubling times are not different between both oxygen concentrations and EPO did not influence the proliferation of cells at different concentrations (E). As control for a positive EPO-response, HCD-57 cells were used (D). Data are presented as mean ± SEM, n = 3-11 in triplicates.