title: Effects of Ca/Pi ratio, Ca2+ x Pi ion product, and pH of incubation fluid on accumulation of 45Ca2+ by matrix vesicles in vitro.
abstract: The capacity of matrix vesicles (MV) to induce mineralization under various electrolyte conditions has not been explored. Accordingly, we examined the ability of isolated MV to induce calcification using synthetic lymphs with ranges of Ca/Pi ratio, Ca2+ x Pi ion product, and pH relevant to both normal and pathological conditions. At a fixed ion product of 2.84 mM2, 45Ca2+ uptake was supported at all Ca/Pi ratios tested, with ratios of 1.3-1.4 being optimal. Rapid ion uptake became saturated at levels greater than 2.7 mM2 when studied at a fixed Ca/Pi = 1.3, indicating a rate-limiting membrane ion porter. However, treatment of MV with non-ionic detergent did not destroy their ability to induce mineralization. At constant Ca/Pi of 1.3 and Ca2+ x Pi of 2.63 mM2, maximal uptake rates occurred at pH 7.6-7.8 over a pH range of 7.0-8.0, with significant uptake being supported only over the narrow range of pH 7.4-7.8. Studies showing that the effects of pH on amorphous calcium phosphate (ACP)-mediated calcification were very similar to those of MV, indicate that a stabilized form of internal ACP may induce crystalline mineral formation during MV-mediated calcification.
authors.affiliation: Department of Chemistry, University of South Carolina, Columbia 29208.
authors.forename: W B
authors.initials: WB
authors.lastname: Valhmu
authors.forename: L N
authors.initials: LN
authors.lastname: Wu
authors.forename: R E
authors.initials: RE
authors.lastname: Wuthier
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D002130:Calcium Phosphates / Q000378:metabolism; D002132:Calcium Radioisotopes / Q000493:pharmacokinetics; D002356:Cartilage / Q000378:metabolism; D002478:Cells, Cultured; D002645:Chickens; D003470:Culture Media / Q000494:pharmacology; D006132:Growth Plate / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D006863:Hydrogen-Ion Concentration; D006882:Hydroxyapatites / Q000378:metabolism; D002479:Inclusion Bodies / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D017830:Octoxynol; D010758:Phosphorus / Q000378:metabolism / Q000494:pharmacology*; D011092:Polyethylene Glycols / Q000494:pharmacology
chemical_list: D002130:Calcium Phosphates; D002132:Calcium Radioisotopes; D003470:Culture Media; D006882:Hydroxyapatites; C519480:amorphous calcium phosphate; D010758:Phosphorus; D011092:Polyethylene Glycols; D017830:Octoxynol; D002118:Calcium