ADHESIVE SUBSTRATES INFLUENCE ACID-PRODUCTIVE ACTIVITIES OF CULTURED RABBIT OSTEOCLASTS - CULTURED OSTEOCLASTS WITH LARGE VACUOLES HAVE ENHANCED ACID-PRODUCTIVE ACTIVITIES

Since acid secretion of polarized osteoclasts on the bone surface has an important role in bone resorption, we examined the acid-productive activities of osteoclasts by measuring the pH of acidic organelles suc h as endosomes, lysosomes, and vacuoles in cultured rabbit osteoclasts with FITC-dextran as a fluorescent pH probe. The average pH value of acidic organelles of osteoclasts cultured on plain glass coverslips wa s 5.3 +/- 0.2. The pH of the acidic organelles correlated well with th e size and amount of the vacuoles in the cells. Using this FITC-dextra n method, we also examined the effects of adhesive substrates, such as type I collagen, vitronectin, and dentine, on the acid-productive act ivities of osteoclasts and found that the pH value of acidic organelle s of osteoclasts cultured on dentine slices was significantly lower th an that of osteoclasts cultured on plain glass coverslips. Likewise, i n the case of the osteoclasts cultured on type I collagen- or vitronec tin-coated glass coverslips, the pH values of acidic organelles were s lightly lower and the proportion of osteoclasts having large vacuoles was increased compared with the cells cultured on the plain glass cove rslips. These results indicate that osteoclasts containing large vacuo les have high acid-productive activities, and adhesive substrates such as type I collagen and vitronectin influence the formation of large v acuoles in cultured osteoclasts. (C) 1995 Academic Press, Inc.