Distribution of integrin subunits on rat metaphyseal osteoclasts and osteoblasts.

A key event in bone resorption is the attachment of osteoclasts to the bone matrix. The process apparently involves integrin plasma membrane receptors for extracellular matrix proteins. In the present study the distribution of some integrin subunits among different osteoclastic and osteoblastic domains was determined using immunocytochemistry on rat metaphyseal bone. Ultrathin cryosections were incubated with polyclonal antibodies against the alpha v beta 3 integrin and against the individual integrin subunits, alpha v, beta 1, beta 3, and beta 5. Bound antibodies were detected with 10-nm colloidal gold coated with protein A. The results show that alpha v- and beta 3-subunits are enriched at the osteoclast plasma membrane facing the bone matrix, i.e., the clear zone. Furthermore, beta 1- and beta 5-subunits were somewhat enriched at the osteoblast plasma membrane facing the bone surface. The present observations corroborate and extend our previous data indicating that the alpha v beta 3 integrin mediates tight attachment of the osteoclast to the bone matrix. Moreover, a role for integrins in the attachment and interactions of the osteoblast is suggested.