Figure 1. Experimental design.

Cells were subjected to cycling (interchanging periods of 1% and ambient oxygen), chronic hypoxia (constant 1% oxygen) or control conditions (ambient oxygen) for 72 hours. The scheme predominantly shows the time scale of cycling hypoxia, which consisted of the following periods of hypoxia (1% oxygen) and reoxygenation (21% oxygen): 1%–4 hours, 21%–4 hours, followed by two cycles of 1%–12 hours, 21%–4 hours, 1%–4 hours, 21%–4 hours, followed by 4 hours of reoxygenation.