Responses of articular cartilage explant cultures to different oxygen tensions

Bovine articular cartilage explants were cultured under atmospheres of 6, 10, 24, 66 and 91% oxygen. [35S]Glycosaminoglycan, chondroitin sulphate and keratan sulphate synthesis were measured together with the pool size of UDP-N-acetylhexosamines, UDP-hexoses and UDP-glucuronate. UDP-xylose was not detected. [35S]Glycosaminoglycan synthesis was maintained at the same level as in fresh tissue when cultured over 7 days with 20% foetal calf serum present and under a 6% oxygen tension. Under normal atmosphere (24%) synthesis was stimulated and remained elevated throughout the incubation period. Under higher oxygen tensions, initial stimulation of glycosaminoglycan synthesis was followed by progressive inhibition. The [35S]chondroitin sulphate/keratan sulphate ratio was constant (approximately 16:1) between 6 and 24% oxygen tension, but increased to 50:1 at 91% oxygen. The UDP-N-acetylhexosamine pool was larger under anaerobic (6, 10%) and excessively aerobic (66, 91%) oxygen tensions than under a normal atmosphere (24%). The UDP-hexose pool was expanded under anaerobic conditions. The UDP-glucuronate pool showed little variation between 6 and 24% oxygen tensions, but contracted under very aerobic conditions. We found no evidence indicating that keratan sulphate synthesis was favoured under anaerobic conditions to compensate for decreasing chondroitin sulphate synthesis.