Osteoclastic bone resorption: in vitro analysis of the rate of resorption and migration of individual osteoclasts.

Osteoclasts isolated from the long bones of newborn rabbits were cultured on translucent devitalized bone slices and observed by phase-contrast time-lapse cinemicrography and scanning electron microscopy (SEM). This has allowed us to measure the rate of resorption and the rate of migration of individual osteoclasts. Our films show that osteoclasts do not resorb while migrating. When the osteoclastic resorption areas, which are easily recognizable with phase-contrast microscopy as areas delineated by refractile lines, were observed by SEM, such areas appeared as excavated areas lined with a network of collagen fibrils. The rate of migration was calculated using time lapse recordings, and varied from 30 micron/hr to 248 micron/hr, with a mean +/- SEM of 105 +/- 10 micron/hr. The rate of resorption by individual osteoclasts was calculated using both time lapse and SEM data, and varied from 43 micron 3/hr to 1225 micron 3/hr with a mean +/- SEM of 390 +/- 109 micron 3/hr. Additional observations indicated not only that the same osteoclast can resorb at a different rate at different times without any definable alteration of the culture conditions, but also that the same osteoclast can simultaneously resorb two lacunae at different rates. These observations provide, for the first time, data on the rate of resorption and the rate of migration of individual osteoclasts on a bone substratum.