A comparative study of osteoclasts: in situ versus smear specimens.

Osteoclasts residing on rims and walls of bony concavities on remodeling proximal tibia from growing rats were examined by light microscopy following stripping of the periosteal connective tissue layer. Comparison of these cells in situ and after transfer to glass slides revealed the presence of numerous mononucleate osteoclasts, as well as typical multinucleate forms, all exhibiting a ruffled border and acid phosphatase and succinic dehydrogenase activity. Macrophage-like cells were situated adjacent to osteoclasts in situ. Osteoblasts were relatively inconspicuous. The possibility that the basic functional osteoclast unit is a mononucleate cell is discussed.