Characterization of subpopulations of OC and OB bone cells obtained by sedimentation at unit gravity.

Immediately after isolation from calvaria, OC and OB bone cells populations 1-6 were individually characterized by sedimentation at unit gravity. This procedure was used to generate from each population 4 fractions that contained cells of different sizes. Sedimentation results suggested that freshly isolated OC cell populations consisted of cells that were generally smaller and demonstrated less size heterogeneity than OB cells. After sedimentation the cells in each fraction were cultured for 6 days and then characterized with regard to cell separation based on basal biochemical characteristics and hormonal responses to PTH and CT. The largest cells in the later released OC cells appeared to be a mixture of OC and OB cells (approx. 15% of populations 2 + 3). All OB cell fractions appeared to be free of OC cells. The highest basal OC activities and hormonal responses occurred in the larger cells of population 2, whereas in OB cells (populations 5 and 6), this occurred in the cells of small to intermediate size. Finally, although the absolute size of the cells in each fraction increased during culture, the size differential within the fractions and between OC and OB cells was maintained even after 6 days.