Document Detail


An ultrastructural study of the effects of acidic phospholipid substitutions on calcium phosphate precipitation in anionic liposomes.
MedLine Citation:
PMID:  1315188     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
A model membrane system was used to investigate the ability of specific membrane constituents to modulate the precipitation of calcium phosphate. Intraliposomal precipitation was induced in phosphate-encapsulated liposomes composed of 7:2:1 molar mixtures of phosphatidylcholine (PC), dicetyl phosphate (DCP), and cholesterol (Chol) by ionophore-supported (X-537A) Ca2+ uptake. Extraliposomal precipitation occurred when these reactions were initiated in metastable external solutions. In this case, the endogenously formed crystals penetrated through the enclosing lipid bilayers and seeded the external solution phase. Transmission electron microscopy (TEM) was used to monitor the effect of acidic phospholipids [phosphatidic acid (PA), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylglycerol (PG)] on the precipitation reactions when these molecular species were incorporated into the liposome membranes. Compared with the precipitation reactions in 7PC:2DCP:1Chol liposomes containing no acidic phospholipids, calcium phosphate formation in the presence of monoester phosphate (PA) and amino- (PS) phospholipids was inhibited. Analyses of the lipid-mineral interactions in PA-containing (10 mol%) liposomes revealed close physical contact between the small crystals of apatite and the inner lipid bilayers; there was only minimal extraliposomal precipitation. A few small crystals adhered to the external surfaces of the liposomes. In PS-containing liposomes, lipid-mineral interactions were dependent upon the DCP content of the lipid membrane. Discrete clusters of crystals formed within the interior aqueous compartment when intraliposomal precipitation was initiated in 7PC:2DCP:1Chol liposomes doped with up to 10 mol% PS. There was no evidence for specific associations between these crystals and the enclosing lipid bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)
Authors:
B R Heywood; E D Eanes
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Calcified tissue international     Volume:  50     ISSN:  0171-967X     ISO Abbreviation:  Calcif. Tissue Int.     Publication Date:  1992 Feb 
Date Detail:
Created Date:  1992-06-01     Completed Date:  1992-06-01     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7905481     Medline TA:  Calcif Tissue Int     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  149-56     Citation Subset:  IM    
Affiliation:
Bio-inorganic Chemistry Laboratory, School of Chemistry, University of Bath, Claverton Down, UK.
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MeSH Terms
Descriptor/Qualifier:
Durapatite
Hydroxyapatites / chemistry*
Liposomes / chemistry*
Microscopy, Electron
Phosphatidic Acids / chemistry
Phosphatidylglycerols / chemistry
Phosphatidylinositols / chemistry
Phosphatidylserines / chemistry
Phospholipids / chemistry*
Chemical
Reg. No./Substance:
0/Hydroxyapatites; 0/Liposomes; 0/Phosphatidic Acids; 0/Phosphatidylglycerols; 0/Phosphatidylinositols; 0/Phosphatidylserines; 0/Phospholipids; 1306-06-5/Durapatite

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