Effects of fluoride on in vitro calcification of tendon matrix
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Ca2+ and Pi uptake induced in vitro by a collagenous matrix derived from bovine tendon is inhibited by 1×10−6 to 2×10−5M NaF and stimulated by 2×10−5 to 2×10−3M NaF. Fluoride uptake occurs only over the latter concentrtion range. The uptake of Ca2+, Pi, and F−1 progresses toward a limiting extent at which the molar Ca/P and Ca/F values are 1.6 to 1.7 and 4.5 to 5.7, respectively. Although the matrix-bound mineral, previously formed in the absence of NaF, readily undergoes dissolution when exposed to a Ca2+- and P-free medium of pH<7.4, the bound mineral phase formed in the presence of NaF does not. We conclude that fluoroapatite is the primary matrix-bound mineral. The uptake of fluoride, Ca2+. and Pi by both uncalcified and previously calcified matrices is inhibited by methylenediphosphonate and by phosphonoacetate as is calcification in the absence of NaF. Kinetic studies indicate that formation of a CaP complex precedes the uptake of F−1 and suggest that F−1 and OH−1 compete for interation with the CaP complex during the calcification process. We concluded that fluoroapatite formation induced by the collagenous matrix occurs by a multistep pathway comparable to that proposed previously for hydroxyapatite formation.
Key wordsCollagen Calcification Fluoroapatite Nucleation Inhibitors
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