Immunohistochemical Localization of Calcitonin Receptor in Mouse Tibiae.

We have raised specific antisera against the extracellular domain of the rat/mouse calcitonin receptor (CTR), consequently immunolocalizing the CTR-positive cells in mouse tibiae. As expected, the immunoreactivity for the CTR was intensely detected in cells identical to tartrate-resistant acid phosphatase (TRAP) positive multinucleated osteoclasts and mononuclear cells, whereas no immunoreactivity was detected in osteoblasts and bone marrow cells. Most osteoclasts on the bone surface possessed the CTR, therefore indicating that bone resorbing osteoclasts could be prompted to respond to endogenous calcitonin. Immuno-electron microscopy revealed CTR-immunoreactivity mainly on the plasma membranes including the pits associated with the cell membranes, and sometimes on intracellular translucent vacuoles and in the vesicles in the vicinity of the Golgi apparatus in the osteoclasts. These results lead to the postulation that CTR is chiefly localized to the cell surface of osteoclast, but is subjected to continuous internalization followed by the receptor-transport to the Golgi apparatus.