Fine structure of rabbit ear chondrocytes in vitro and after autotransplantation

Chondrocytes were isolated enzymatically from rabbit ear cartilage, grown in vitro or as autotransplants for 1, 2 or 5 weeks and then examined by transmission electron microscopy. A confluent monolayer formed rapidly in vitro and the cells later grew in multiple overlapping layers, producing thick sheets of cartilaginous tissue. The cells retained a normal structure throughout the period of observation and, like the chondrocytes in intact cartilage, showed numerous microfilaments, and extensive granular endoplasmic reticulum and a prominent Golgi complex. Large amounts of intercellular matrix were laid down in vitro consisting of thin collagen fibrils, small rounded or polygonal granules believed to represent proteoglycans and patches and fibres of elastin. Chondrocytes in intramuscular autotransplants reconstituted an elastic cartilage. The exogenous origin of the cells in the transplants was verified by labeling of the lysosomes by exposure of the cells to colloidal thorium dioxide particles prior to injection. Structurally, the cells and the matrix of the transplants conformed to the above description. Accumulations of elastin-like material were sometimes observed in the Golgi vacuoles of the cells. Extracellularly, such conglomerates aggregated in connection with bundles of microfibrils, building up mature elastic fibres with a dense amorphous structure. The culture and transplant systems characterized here provide suitable experimental models for studies on development, growth and aging of elastic cartilage, including various aspects of the formation and turnover of elastic fibres and other macromolecular matrix components.