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An ultrastructural study of calcium phosphate formation in multilamellar liposome suspensions


Heywood, BR and Eanes, ED, An ultrastructural study of calcium phosphate formation in multilamellar liposome suspensions, Calcified Tissue International, 41, (4) pp. 192-201. ISSN 0171-967X (1987) [Refereed Article]

Copyright Statement

Copyright 1987 Springer-Verlag New York Inc.

DOI: doi:10.1007/BF02555238


Calcium phosphate precipitation can be induced within liposomes containing buffered inorganic phosphate by the ionophore-mediated loading of calcium ions. Negative staining, positive staining for thin sectioning, and freeze-fracture electron microscopy were used to characterize these synthetic vesicles and to evaluate the liposome-mineral interactions resulting from apatite formation. Suspensions of phosphate (050 mM KH2PO4)-encapsulated liposomes were prepared from mixtures of phosphatidylcholine, dicetyl phosphate, and cholesterol in the molar ratios of 7∶2∶1. Precipitation reactions were initiated by first suspending the liposomes in a buffered solution containing calcium (1.32.2 mM Ca(NO3)2) and then adding the cationic ionophore X-537 A. All experiments were carried out at 22C, pH 7.4, and 240 mosm. Transmission electron microscopical analysis showed that the liposome preparation consisted of multilamellar, multicompartmental vesicular structures. The liposomes were typically heterogeneous with respect to both the size and number of phospholipid bilayers surrounding the aqueous cores. In Ca-loaded liposomes, discrete clusters of apatite mineral were present within the lumen, and in close proximity to the inner lipid membranes. These nascent crystallites eventually penetrated the lipid envelope to provide a focus for external precipitation events. Crystalline apatite phases were not observed when the incubation conditions prevented intraliposomal precipitation. The de novo calcification of these liposomes had many features in common with the sequence of mineral deposition occurring in matrix vesicle-mediated calcification. These results reinforce the conclusions of earlier chemical and kinetic studies and further support the use of this system as an experimental model for examining the membrane-mineral interactions associated with tissue mineralization.

Item Details

Item Type:Refereed Article
Keywords:apatite, liposomes, matrix vesicles, TEM
Research Division:Biomedical and Clinical Sciences
Research Group:Medical biochemistry and metabolomics
Research Field:Medical biochemistry - inorganic elements and compounds
Objective Division:Health
Objective Group:Clinical health
Objective Field:Clinical health not elsewhere classified
UTAS Author:Heywood, BR (Professor Brigid Heywood)
ID Code:104348
Year Published:1987
Web of Science® Times Cited:23
Deposited By:Research Division
Deposited On:2015-11-10
Last Modified:2015-12-18

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