Ultrastructure of timed isolates of in vitro canine articular chondrocytes

Articular chondrocytes were enzymatically isolated from the distal end of the adult canine femur. The digestion procedure was conducted for 2- or 6-hour intervals, using 0.25% trypsin and 0.25% collagenase. Cells grown from the 2-hour digestion procedure were polygonal to stellate, had large vesicular nuclei with prominent nucleoli, and exhibited contact inhibition at confluency. Cells grown in cultures from the 6-hour digestion procedure were fusiform, had prominent nuclei with numerous nucleoli, and lacked contact inhibition. Cell cultures established, using cells from both procedures, were examined using the transmission electron microscope. Ultrastructurally, an extensive granular endoplasmic reticulum, prominent golgi complexes, and numerous autophagic vacuoles characterized the 2-hour cell population. The fine structures of the cells grown from the 6-hour process were characterized by numerous cytoplasmic microfilaments randomly dispersed and marginated beneath the plasmalemma of the cells. An extensive dilated rough-endoplasmic reticular system was present. The chondrocytes described in the present study provided morphologic evidence of a heterogeneous cell population in adult canine articular cartilage.