MULTINUCLEATED GIANT-CELLS RECRUITED BY IMPLANTATION OF OCTACALCIUM PHOSPHATE (OCP) IN RAT BONE-MARROW SHARE ULTRASTRUCTURAL CHARACTERISTICS WITH OSTEOCLASTS

The ultrastructural characteristics of multinucleated giant cells (MNG Cs) on octacalcium phosphate (OCP) and hydroxyapatite (HA) were invest igated in comparison with those of osteoclasts, when the synthetic OCP and HA were implanted in rat bone marrow. The morphological differenc e in the MNGCs were shown between OCP and HA implants in 2 weeks after implantation. The MNGC on the implanted OCP (i-OCP) developed the ruf fled border-like structure and the clear zone-like structure. The i-OC P was frayed where it was in contact with the ruffled border-like stru cture. The MNGC on the implanted HA (i-HA) developed the clear zone-li ke structure, whereas no ruffled border was seen. The surface of i-HA associated with the MNGC was smooth and not frayed. Bone formed direct ly on the OCP or HA implants. The interface between the i-OCP and bone matrix interdigitated, whereas that between the i-HA and bone matrix was comparatively smooth. The present study suggested that the i-OCP c ould be resorbed by the MNGCs which share some ultrastructural charact eristics with osteoclasts.