Organization of osteoclast microfilaments during the attachment to bone surface in vitro.

Rat and chicken osteoclasts were cultured on bone slices, where they showed active resorption with resorption lacunae, which cold be seen by toluidine blue staining or with a scanning electron microscope. Osteoclast microfilaments, F-actin, vinculin, and talin were studied by immunofluorescence. In attached osteoclasts, vinculin appeared as a double circle in the periphery of the cell, and the most intense F-actin staining was located between these vinculin zones. Some chicken osteoclasts showed also intense F-actin staining throughout the center of the cell. Talin appeared in a similar double circle to vinculin. This kind of distribution of microfilaments was always associated with resorption lacunae, and F-actin, vinculin, and talin zones correspond roughly to the edge of lacunae. Osteoclasts showing a diffuse staining pattern were not associated with a resorption pit. The results suggest that this specific microfilament arrangement is located at the attachment zone of the osteoclast and is obligatory for the attachment and resorption. However, this arrangement of microfilaments is quite different from the one that has been previously described in osteoclasts cultured on glass.