Mechanical fragmentation and transportation of calcium phosphate substrate by filopodia and lamellipodia in a mature osteoclast

The functions of filopodia and lamellipodia in mature osteoclasts are not well known in the process of bone resorption. We investigated the function of filopodial/lamellipodial movement in mature osteoclasts by video-enhanced contrast-differential interference contrast (VEC-DIC) microscopy. Mature osteoclasts, which were isolated from Japanese white rabbits, were cultured on calcium phosphate (CP)-coated quartz coverslips to observe filopodial/lamellipodial movement and the formation of CP-free areas precisely. Filopodia broke the CP substrate into pieces and transported them to the cell body by capturing them at the tip. Lamellipodia destroyed the CP substrate, and transported it to the cell body by capturing small particles in a mass. This study suggests two functions of filopodia and lamellipodia in mature osteoclasts, i.e., the mechanical fragmentation of the CP substrate and the transportation of the CP particles to the cell body.