Effects of O2 tension and glucose concentration on the cellular respiration of equine articular chondrocytes in culture.

In vivo, articular chondrocytes are exposed to 5 to 10% O21,2. Chondrocytes are also suspected to produce reactive oxygen species when submitted to anoxia/re-oxygenation3,4. We were interested to study the effects of O2 and glucose variations on cellular respiration, glucose consumption and lactate production. Equine articular chondrocytes were cultured in suspension for 2 days under 5 or 21 % O2 in the gaseous phase, and with 0, 1.0 or 4.5 g/L glucose. The viable cells were then counted and the respiration rate (O2 consumption) of 10.106 cells was monitored by oxymetry for 2 hours; after oxymetry, glucose and lactate were measured in the medium (enzymatic assays). After 2 days, the cell viability was the best at 5% O2 and 1g/L glucose; it decreased at 4.5 g/L glucose and was the worst at 0g/L glucose, for the two O2 tensions (n=3). There was no obvious difference of the respiration rate between cells cultured at 5 and 21% O2, but respiration of chondrocytes was surprisingly low. When cells were submitted to 20 min anoxia at 0% O2, the O2 consumption was doubled at re-oxygenation for cells previously cultured at 21% O2. Glucose and lactate values found in the medium after oxymetry : lactate release in medium was similar (36.23 and 34.57 mg/L respectively) for cells cultured with 1g glucose and 5 or 21% O2 conditions; lactate values were low (2.03 and 8,63 mg/L respectively) for 4.5 g glucose and 5 or 21% O2. Glucose uptake was not different whatever the culture conditions. These results indicate a low cellular respiration with a lactate production linked to the glucose concentration in the medium, and raise the question of the capacity of chondrocytes to produce ROS in vivo starting from the mitochondrial chain.