Effect of medium pH on osteoclast activity and osteoclast formation in cultures of dispersed rabbit osteoclasts

We investigated the effect of medium pH on activity of isolated osteoclasts and have also looked at the possibility that medium pH affects osteoclast numbers during culture. Osteoclast-containing cell suspensions prepared from neonatal rabbits were cultured on bovine bone slices at pH 6.5, 7.0, or 7.5. After 24 or 48 h of culture, the cells and bone slices were fixed and stained for tartrate-resistant acid phosphatase (TRAP). After counting the osteoclasts, the cells were removed and the resorption lacunae stained by immunostaining using anticollagen type I antibody and then quantitated. We found that the resorptive activity of isolated rabbit osteoclasts was sharply increased at pH 6.5-7. Osteoclast differentiation and proliferation, on the other hand, were optimal at pH 7.0-7.5 but decreased at pH 6.5. The results thus imply that pH regulation of the bone surface environment can dramatically alter both the number of osteoclasts and their resorptive activity.