BONE-CELLS AND MATRIX BIND CHEMICALLY-MODIFIED NONANTIMICROBIAL TETRACYCLINE

H-3-labeled chemically modified, non-antimicrobial tetracycline (4-de- dimethyl-aminotetracycline; CMT) was injected intraperitoneally into n eonatal fats and the animals killed at 20 min, 2 or 4 h after isotope injection. The binding of H-3-CMT in the calvariae was localized by li ght and electron microscopic autoradiography. At 20 min after injectio n, a high level of bound 3H-CMT was localized in the cells of the peri osteum including the osteoblasts and preosteoblasts. The newly formed bone matrix was also heavily labeled by silver grains. At the ultrastr uctural level, many silver grains appeared over the cytoplasm of osteo blasts and preosteoblasts, particularly along the plasma membranes, in the periosteum. At 2 and/or 4 h after isotope injection, the number o f silver grains over the cells was markedly reduced but that over the bone matrix appeared unchanged. These results indicate that, in additi on to the mineral phase of bone, CMT directly binds to (or is taken up by) osteogenic cells and is then rapidly metabolized by these cells.