SURFACE BINDING AND CLEARANCE OF CALCITONIN BY AVIAN OSTEOCLASTS

Osteoclasts, isolated from chick tibias and maintained in culture for 4-6 days, were treated with biotinylated calcitonin followed by fluore scent avidin. In 2 min the entire cell surface fluoresced, by 7.5 min fluorescence was centrally clustered and by 10 min fluorescence had di minished to background levels. Specific binding was blocked by excess unlabeled calcitonin and not influenced by unrelated peptide, The resu lts show that avian osteoclasts bind calcitonin specifically and that the bound calcitonin is rapidly cleared from the cell surface, which i ndicates involvement of receptor-mediated endocytosis.