Effect of different hypoxic conditions on GAPDH mRNA expression in U251 cells. Cells were cultured 24 h under normoxic conditions or for 1 h, 6 h or 24 h under hypoxic (0.1%, 1%, 5% O2) conditions. Reoxygenation experiments were performed for 24 h and 48 h after 24 h hypoxia. DFO served as hypoxia-positive control. (A) Semiquantitative RT-PCR analysis of GAPDH and β-actin mRNA expression. Shown is one representative experiment out of three. (B) Bar graphs showing GAPDH expression strength after densitometric evaluation of the PCR bands and normalization to the corresponding expression of β-actin. GAPDH mRNA expression was not regulated by hypoxic conditions.