Communication between paired chondrocytes in the superficial zone of articular cartilage.

The regeneration and repair of cartilage damaged by injury or disease, a major goal of orthopaedic science, depends on understanding the structure and function of both the extracellular matrix and the chondrocytes. In this study, we explored the in situ organization and potential interactions between chondrocytes in the superficial zone of adult rabbit articular cartilage. Some chondrocytes in this zone were observed close together and appeared to be paired whereas others were solitary. The shared surfaces of a chondrocyte pair were separated by a narrow plate of extracellular matrix, into which extended small cytoplasmic projections from both cells. Furthermore, the spatial distribution of major cellular landmarks, such as the nucleus and centrosome as well as some intracellular proteins such as connexin-43, tended to be mirrored about this matrix plate. Fluorescence recovery after photobleaching revealed the fluorescent dye calcein-AM dye can pass between paired cells, and that the passage of this dye can be inhibited by the gap junction blocker octanol. These results illustrate that rapid cellular communication is possible between cells in the superficial layer of adult articular cartilage, which challenges the current thinking that these chondrocytes function in isolation.