Fig. 4. PDL-L2 cells produce mineralized nodules in response to rhBMP-2. Cells were cultured for 3 days in the differentiation medium. Cells were then given either 250 ng/ml rhBMP-2 or vehicle and incubated for an additional 3 days. Cells were cultured for a further 25 days without any treatment in the differentiation medium. The medium was changed every 3 days. Cultured cells were fixed and subjected to Arizalin red-S staining (A). Original magnification was x4. After being photographed, each culture dish was subjected to the destaining process (see text for detail), and the Arizalin red-S concentration was determined by absorbance at 562 nm. Note that the extent of mineralization of PDL cells, a mixture of various cells from PDL, is even higher than that of MC3T3-E1 cells (B). See text for details.