AJP - Cell Physiology, Vol 266, Issue 3 C590-C600, Copyright © 1994 by American Physiological Society
pH-dependent multilamellar structures in fetal mouse bone: possible involvement of fatty acids in bone mineralization
T. Takahashi, S. Ueda, K. Takahashi and R. O. Scow
Department of Oral Anatomy, Kanagawa Dental College, Yokosuka, Japan.
pH-dependent multilamellar structures in fetal mouse bone: possible
involvement of fatty acids in bone mineralization. Am. J. Physiol. 266
(Cell Physiol. 35): C590-C600, 1994.--Multilamellar structures (MLS) were
found inside and outside osteoblasts in cultured and uncultured fetal mouse
parietal bone fixed at pH 7.3 with glutaraldehyde solution containing
tannic acid (TA). Electron-lucent areas (up to 1.5 microns in diameter)
surrounded by thin lamellar structures were found in place of MLS in bone
and bone cell cultures fixed at pH 6.0 in the presence of TA. Large lipid
droplets were found, in place of electron-lucent areas and MLS, in
specimens fixed at pH 7.4 in the absence of TA and dehydrated with a
procedure that did not extract neutral lipid. Freeze-fracture studies
showed phosphatidylcholine formed MLS at both pH 8.1 and pH 6.0, whereas
oleic acid formed MLS at pH 8.1 and lipid droplets at pH 6.0. Thus fatty
acids probably formed the pH-dependent MLS found in bone. The data suggest
that osteoblasts synthesize and secrete fatty acids, as droplets, into the
extracellular space. The close association of MLS with calcifying osteoid
in specimens processed with TA suggests that fatty acids are directly
involved in bone mineralization.
