REMOVAL OF OSTEOCLAST BONE-RESORPTION PRODUCTS BY TRANSCYTOSIS

Osteoclasts are multinucleated cells responsible for bone resorption. During the resorption cycle, osteoclasts undergo dramatic changes in t heir polarity, and resorbing cells reveal four functionally and struct urally different membrane domains. Bone degradation products, both org anic and inorganic, were endocytosed from the ruffled border membrane. They were then found to be transported in vesicles through the cell t o the plasma membrane domain, located in the middle of the basal membr ane, where they were liberated into the extracellular space. These res ults explain how resorbing osteoclasts can simultaneously remove large amounts of matrix degradation products and penetrate into bone.