Endothelin-1 localization in bone cells and vascular endothelial cells in rat bone marrow

Endothelin-1 (ET-1) localization in bone cells and associated vascular endothelial cells in metaphyseal bone marrow of the rat femur was examined by a biotin-streptoavidin-horseradish peroxidase method in paraffin sections and by indirect immunogold techniques in post-embedded ultrathin sections. Mouse anti-ET-1 monoclonal antibody was used as the primary antibody. In metaphyseal bone marrow, intense immunostaining was observed over osteoclasts, osteoblasts, young osteocytes, and vascular endothelial cells. But bone and cartilage matrices and chondrocytes in the proliferating zone were negative for immunoreaction. At the subcellular level, specific immunogold labeling was localized along plasma membranes and in the cytoplasm including those of ruffled borders and clear zones of osteoclasts. Some colloidal gold particles were also detectable within pale vacuoles of osteoclasts. Immunoreactivity was also found along the plasma membranes, cisterns of rough-surfaced endoplasmic reticulum, mitochondria, and cytoplasmic matrices of osteoblasts, but was less intense than that of osteoclasts. In endothelial cells of blood capillaries in close proximity to bone cells, intense immunolabeling occurred over the cytoplasm. None of the cases examined showed accumulation of immunogold particles in the secretion granules of these cells.