The effect of oxygen tension on calcium homeostasis in bovine articular chondrocytes

• Main Authors: Gibson John S, White Rachel
• Format: Article
• Language: English
• Published: BMC 2010-04-01
• Series: Journal of Orthopaedic Surgery and Research
• Online Access: http://www.josr-online.com/content/5/1/27
• ISSN: 1749-799X

<p>Abstract</p> <p>Background</p> <p>Articular chondrocytes normally experience a lower O₂tension compared to that seen by many other tissues. This level may fall further in joint disease. Ionic homeostasis is essential for chondrocyte function but, at least in the case of H⁺ions, it is sensitive to changes in O₂levels. Ca²⁺homeostasis is also critical but the effect of changes in O₂tension has not been investigated on this parameter. Here we define the effect of hypoxia on Ca²⁺homeostasis in bovine articular chondrocytes.</p> <p>Methods</p> <p>Chondrocytes from articular cartilage slices were isolated enzymatically using collagenase. Cytoplasmic Ca²⁺levels ([Ca²⁺]_i) were followed fluorimetrically using Fura-2 to determine the effect of changes in O₂tension. The effects of ion substitution (replacing extracellular Na⁺with NMDG⁺and chelating Ca²⁺with EGTA) were tested. Levels of reactive oxygen species (ROS) and the mitochondrial membrane potential were measured and correlated with [Ca²⁺]_i.</p> <p>Results</p> <p>A reduction in O₂tension from 20% to 1% for 16-18 h caused [Ca²⁺]_ito approximately double, reaching 105 ± 23 nM (p < 0.001). Ion substitutions indicated that Na⁺/Ca²⁺exchange activity was not inhibited at low O₂levels. At 1% O₂, ROS levels fell and mitochondria depolarised. Restoring ROS levels (with an oxidant H₂O₂, a non-specific ROS generator Co²⁺or the mitochondrial complex II inhibitor antimycin A) concomitantly reduced [Ca²⁺]_i.</p> <p>Conclusions</p> <p>O₂tension exerts a significant effect on [Ca²⁺]_i. The proposed mechanism involves ROS from mitochondria. Findings emphasise the importance of using realistic O₂tensions when studying the physiology and pathology of articular cartilage and the potential interactions between O₂, ROS and Ca²⁺.</p>