Localization of endothelin-1 in the osteoclast.

Endothelin-1 (ET-1) localization in osteoclasts in the metaphyseal bone marrow of the femur was examined by indirect immunogold techniques in post-embedded ultrathin sections. Mouse anti-ET-1 antibody and anti-mouse IgG conjugated with colloidal gold particles were used as the primary and secondary antibodies, respectively. Specific immunolabeling was localized along the plasma membranes, the cytoplasm including those of ruffled borders and clear zones, and pale vacuoles of osteoclasts. In addition, intense immunolabeling was present over the cytoplasm of vascular endothelial cells in close proximity to osteoclasts. These results suggest that osteoclasts are target cells for ET-1.