Functional and morphological alterations in chondrocytes undergoing apoptosis. Chondrocytes were treated with 5 mM inorganic phosphate (Pi) for 4 hours (A and D), 8 hours (B and E), and 24 hours (C and F). Differential interference contrast (A-C) and fluorescence (D-E) microscopy images of the same cells are shown. Functional mitochondria were labeled with TMRE (red fluorescence in D-E), and chondrocyte DNA was labeled with Hoechst dye 33342 (blue fluorescence in D-E). Note the presence of numerous vesicles in the cytoplasm (arrowhead in B) of a dying chondrocyte. At 24 hours after initiation of Pi treatment, the chondrocyte shows obvious signs of apoptosis: loss of attachment, shrinkage, blebbing (arrowhead in C), and apoptotic bodies containing DNA (arrowheads in F)