Oxygen Tension Variation in Ischemic Gastrocnemius Muscle, Marrow, and different Hypoxic Conditions In Vitro

BACKGROUND: Bone marrow stromal cells (BMSCs) play an important role in ischemic limb angiogenesis. BMSCs cultured in vitro can be exposed to oxygen tension much higher than that experienced in vivo. This study assessed oxygen tension in bone marrow and ischemic muscle in vivo, and then identified an appropriate oxygen concentration for culturing BMSCs. MATERIAL/METHODS: Unilateral hind limb ischemia was surgically induced in 30 mice, and tissue oxygen tension in bilateral gastrocnemius muscles and femoral bone marrow was monitored in vivo using a micro-electrode at 24 hours, 1 week, 2 weeks, and 3 weeks after modeling. Media used for culturing normal marrow, muscle, and artery tissue were incubated with various oxygen concentrations, and O(2) tension was continuously monitored. Oxygen tension in aortic arterial blood was monitored using a micro-electrode and blood gas analyzer, and the results were compared. RESULTS: Oxygen tension in ischemic gastrocnemius muscle reached a nadir at 1 week after ischemic modeling, when histological changes were most noticeable. Culture media incubated with 3%, 6%, and 14% oxygen (the normal oxygen levels of bone marrow, muscle, and arterial blood, respectively) required 9, 6, and 2 hours, respectively, to reach an equilibrated oxygen tension, and oxygen tension was elevated by 1.6-, 1.2-, and 0.4-fold, respectively, upon re-exposure of the media to air. CONCLUSIONS: Physiological oxygen tension differs in different tissues. A 3% O(2) concentration mimics the physiological O(2) exposure experienced by BMSCs and represents the hypoxic concentration. Culture medium incubated under hypoxic conditions requires a prolonged period of time to regain equilibrated oxygen tension.