OSTEOCLAST DEMISE IN THE RAT - PHYSIOLOGICAL VERSUS DEGENERATIVE CELL-DEATH

Time-lapse video microscopy was used to assess the temporal morphologi cal events undergone by rat osteoclasts after exposure to a variety of agents that promote cell death. Direct observations revealed that the re were two morphologically distinguishable forms of cell death, which resembled apoptosis and necrosis, respectively. Marked changes in mor phology became apparent after 2-4 h exposure to a variety of agents, i ncluding cyclosporine A, tamoxifen, corticosterone and dexamethasone. The cells began to shrink rapidly and within 25 min appeared as small round spheres. At this time, the cell membranes underwent violent dist ortive boiling, or zeiosis, accompanied by the formation of small memb rane buds. The cells maintained a spherical configuration and the memb rane appeared to remain intact for several hours. These observations a re consistent with the process of physiological cell death or apoptosi s. In some cases, post-apoptotic changes or secondary necrosis could b e seen, including membrane blebbing and degeneration. In contrast, whe n cells were exposed to hydrogen peroxide or sodium azide, there was a marked deterioration of the cell membrane after 1-4 h. This included the formation of spikes and/or blebbing with the release of intracellu lar debris, resulting in an overall spattered appearance. This type of appearance is characteristic of degenerative cell death or necrosis. The significance of the mode of osteoclast death is discussed.