ISSN:
1432-0827
Keywords:
Electrolytes
;
Phospholipids
;
Cartilage
;
Matrix Vesicles
;
Calcium-phosphate
;
Phospholipid complexes
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
,
Physics
Notes:
Summary Electrolytes and phospholipids of cartilage fractions were partitioned by extraction with organic and aqueous solvents into six solubility groups: Electrolytes I, II and III, and Lipids I, II and III. Of the total Ca, only 4% was water soluble (Electrolytes I); 4–12% was complexed with lipids (Electrolytes II); while the majority (84–92%) was insoluble (Electrolytes III). In contrast, nearly half of the Mg and Pi were water soluble. Of theneutral phospholipid, 95% was not complexed with mineral ions (Lipids I), but 30–45% of theacidic phospholipid was (Lipids II). Ca/Pi ratios were extremely low in the water-soluble phase, but were in the range of amorphous calcium phosphate (ACP) in the insoluble. Molar ratios of the lipid-mineral complex were: Ca∶Mg∶Pi:acidic phospholipid, 4∶3∶2∶2. Mg/Ca ratios in the soluble fraction were high (5.5–8.9), sufficient to stabilize ACP. Kinetic studies revealed rapid turnover of soluble Ca, insoluble turning over much more slowly. Labeling of lipid-complexed Ca was rapid in cells, but occurred later in matrix vesicles, suggesting transfer. While lipid-Ca-Pi complexes can nucleate apatite in vitro, those present in vivo inside matrix vesicles apparently do not because of the excess Mg. We conclude therefore, that in vesicle-mediated calcification, lysis of the membrane may be essential to allow release of internal Mg.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02223311
