Effects of cell density on the expression of differentiation by chick embryo chondrocytes

In this report the effects of cell density on the expression of differentiation by chick embryo sternal chondrocytes is studied. Differentiation is simultaneously assayed in terms of the rate of synthesis of collagen and acid mucopolysaccharide and in terms of the distribution of newly synthesized acid mucopolysaccharide between the cells and the culture medium. Cell density is studied first in terms of the number of cells per plate and second in terms of the size of aggregates of cells. First, when cultures, started‐with 10 4 cells/60 mm dish, are studied over time, it is observed that the rate of synthesis of collagen and acid mucopolysaccharide increases faster than accountable for by the growth rate. Because conditioned medium placed on cultures grown in fresh medium can rapidly enhance mucopolysaccharide synthesis relative to the growth rate, it is suggested that conditioning of the culture medium might contribute in part to the observed rapid acceleration of the expression of differentiation with time in culture. Second, when cultures are started with small inocula so that large aggregates of cells form before cultures reach stationary phase, both the rate of synthesis of specialized products and the ability of cells to retain acid mucopolysaccharides is promoted. It is suggested that accumulated matrix might provide a microenvironment that itself promotes better expression of the cartilage phenotype.