Calcification of cartilage matrix in chondrocyte cultures derived from rachitic rat growth plate cartilage

Abstract

Chondrocytes obtained from collagenase-digested epiphyseal growth plate cartilage of rachitic rats were grown in multilayer cultures. The cultured chondrocytes produced a metachromatic matrix and further electron microscopic examination revealed typical features of cartilage matrix collagen fibrils and matrix vesicles. The alkaline phosphatase activity in cultures was high during the entire 3-week culture period. Acid phosphatase showed a marked increase in activity during the first week of culture. The appearance of apatite crystals in the synthesized matrix was monitored by electron microscopy over a 3-week period. First crystals were consistently found to be associated with matrix vesicles, and in the older cultures calcification spread into the surrounding matrix. No collagen fibrils associated with mineralization were observed during the early culture period. This study clearly demonstrates that in chondrocyte cultures the first mineral crystals were found within or in close association with matrix vesicles. This gives further support to the hypothesis that matrix vesicles are the primary site of mineralization in cartilage. In addition to calcification studies it is suggested that this model is suitable for studying the effects of hormones or other agents on rachitic chondrocytes in vitro.