The occurrence of amorphous mineral deposits in association with the plasma membrane of active osteoblasts in rat and mouse alveolar bone

Abstract

Electron microscopic study of rat and mouse alveolar bone showed that amorphous electron dense deposits are associated with the plasma membranes of osteoblasts and matrix vesicles. The membrane associated amorphous densities are present in tissue fixed in glutaraldehyde alone or in tissue double fixed with glutaraldehyde and osmium tetroxide. The amorphous densities are extracted from ultrathin sections floated on an aqueous solution of 4% EGTA for 1 hour, suggesting that the densities are composed of a calcium-containing mineral. The densities are not associated with the plasma membranes of other bone cells such as osteocytes and osteoclasts, suggesting that they may play a role together with matrix vesicles in the initiation of bone mineralization.