Calcium Homeostasis in Articular Chondrocytes of Two Different Animal Species

Introduction: Intracellular calcium concentration ([Ca2+]i) is a critical parameter in cellular homeostasis, including articular chondrocytes. Perturbed [Ca2+]i of chondrocytes may be associated with joint disease. The objective of the study was to compare large animal models for investigating Ca2+ homeostasis in chondrocytes. Materials and Methods: The gross anatomy of the metacarpophalangeal joint (MCP) of cattle and sheep was compared, along with the effect of various manoeuvres used to study the mechanisms of Ca2+ homeostasis in chondrocytes from load-bearing areas. The gross anatomy was observed before and after dissection, and internal architecture was examined after sectioning. Cartilage thickness was measured with a digital micrometer. Chondrocyte yield was determined after isolation. Chondrocytes were incubated with Fura-2 and Ca2+i followed in different extracellular conditions. A hypotonic shock (HTS) was used to mimic removal of a load. Results: The results showed that ovids and bovids were skeletally immature and aspects of Ca2+ homeostasis were similar. Ovine chondrocytes had higher resting fluorescence, consistent with elevated resting Ca2+ levels. Results from ion substitution experiments were consistent with a role for Na+/Ca2+ exchange, and swelling-induced Ca2+ enters into the cytoplasm via the plasma membrane and intracellular stores. Conclusions: Ca2+ homeostasis in chondrocytes from both species behaved in a similar manner to HTS and ion substitutions. Differences in resting [Ca2+]i could be associated with species, stage of maturation, or Fura-2 itself and require further investigation. These findings contribute to our understanding of the physiology of articular cartilage in different species, and their potential use as models for studying joint disease in humans.