ATP oscillations have a critical role in prechondrogenic condensation during chondrogenesis of ATDC5 cells. (a) Bioluminescence monitoring of PACTIN-PxRe intensity in the culture; the insulin-supplemented medium was changed every other day for 2 weeks. (b and c) Cellular condensation and chondrogenic differentiation were examined with (b) phase contrast images and (c) staining images with FITC-labeled peanut agglutinin of ATDC5 cells 1 week after culturing in medium implemented with insulin plus 2-DG, nifedipine, 2-APB, ionomycin, and thapsigargin, respectively. Scale bars, 100 μm. (d) Effect of 2-DG, nifedipine (Nif), 2-APB, ionomycin (Iono), and thapsigargin (Thaps) on gene expression of type II collagen (COL2A1), aggrecan, and Sox9 1 week after chondrogenic induction. Data show mean±S.D. (n=4). Dunnett's test, **P<0.01 by ANOVA compared with Control (insulin−)