Articular chondrocytes in primary monolayers or subcultures synthesize sulfated macromolecules, presumably mucopolysaccharides. lntracellular 3%04 incorporation by postnatal rabbit chondrocytes reached a steady level by 24 hr of incubation; the nondialyzable extracellular (centrifuged medium + trypsin digest) counts increased over 72 hr, when they were up to 100 times the intracellular value. Cell for cell, radiosulfate counts in each fraction were higher in chondrocytes than fibroblasts. Data from a 3-year-old rabbit were comparable to those from recently weaned animals. Secretion of sulfated mucopolysaccharide was also found in cultures of adult human and bovine articular chondrocytes. Although Ham's F12 medium i s advantageous in establishing a primary culture of chondrocytes, sulfate incorporation was greater when Dulbecco-Eagle medium, with or without supplemental L-proline, was used for subcultures. Ascorbic acid (5 mg/100 ml) added to an already confluent monolayer had no consistent effect.
Isolated chondrocytes cultured in vitro
evolve into 2 cell types: "differentiated" and "dedifferentiated" (1-13) . T h e usual measure of differentiation has been histochemical evidence of matrix production, particularly metachromasia, or autoradiographic demonstration of sulfate fixation. T h e dedifferentiated cells have a fibroblastlike appearance; the differentiated ones are