Calcitonin, prostaglandin E2, and dibutyryl cyclic adenosine 3',5'-monophosphate disperse the specific microfilament structure in resorbing osteoclasts.

Bone resorbing osteoclasts form a specific microfilament structure at the attachment area, in which vinculin and talin appear as a double-circle structure and F-actin fills the space between these circles. This distribution of microfilaments is associated with the resorption lacunae, and F-actin, vinculin, and talin zones correspond roughly to the edges of the lacunae. In the present work, we examined by immunofluorescence the effects of calcitonin (CT) and prostaglandin E2 (PGE2), inhibitors of osteoclastic activity, as well as dibutyryl cyclic AMP (Bt2cAMP) and cytochalasin B, on the microfilament organization in resorbing osteoclasts. CT, PGE2, and Bt2cAMP rapidly dispersed the specific microfilament structure in resorbing osteoclasts. All microfilament proteins studied (vinculin, talin, and F-actin) spread to the central areas of the original circles. The effect of CT was dose dependent. The effects of CT and PGE2 could be reversed, but recovery was slower after CT treatment than after PGE2 treatment. Cytochalasin B entirely destroyed the F-actin organization but only partially the vinculin organization. The results suggest that one structural change leading to the inactivation of the osteoclasts caused by CT and PGE2 is the disintegration of the microfilament structure at the attachment area of resorbing osteoclasts.