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Characterization of the cytoskeleton of isolated chick osteoclasts: effect of calcitonin.

We investigated the effects of calcitonin (CT) and parathyroid hormone (PTH) on the distribution of actin, tubulin, vimentin, and on cell size in cultured chick osteoclasts. In addition, we studied the effects of colchicine on intracellular acidity. Osteoclasts were isolated from the endosteum of 2-3-week chick tibias and were maintained under culture conditions for 5 days. The cells were treated with CT for 30 min or PTH for 60 min and were observed after immunocytochemical staining of cytoskeletal proteins. In untreated cells, actin was found in both a filamentous and a punctate staining pattern, with indented or invaginated regions free of punctate spots. The tubulin distribution in untreated cells was characterized by a pattern of microtubules radiating from the cell center and running parallel to the cell edge. Vimentin staining was usually localized to the perinuclear area. There were no changes in cytoskeletal element distribution or morphology attributable to PTH treatment. Osteoclasts treated with CT were more irregularly shaped, contained more retraction fibers, and were more rounded, with a denser array of cytoskeletal elements in the cell center. In addition, the mean area of the CT-treated cells was significantly less than that of the untreated cells. The actin distribution after CT treatment was still characterized by both a filamentous and a punctate pattern. After CT treatment, vimentin staining appeared more centrally localized than in untreated cells and tubulin staining revealed microtubules which now extended to the retracted cell margin. These results indicate that isolated osteoclasts respond to CT by significant morphological changes which are reflected in the distribution of the major cytoskeletal elements. Disruption of the microtubular system by colchicine treatment also resulted in an initial increase in intracellular acidity, suggesting the involvement of microtubules in the movement of acid-laden vesicles to the exterior.