ABSTRACT
The activity of the matrix vesicles is sensitive to endocrine and growth factor regulation. Interestingly, a number of cell lines which support bone formation when implanted in mesenchymal tissue in vivo produce alkaline phosphatase-enriched matrix vesicles in vitro. Matrix vesicles, organelles produced by the calcifying cells and located in the extracellular matrix, are active in the initial phases of primary mineralization. Experiments with isolated matrix vesicles have also resolved issues concerning organelle function. While bacterial membrane-associated calcification differs in many respects from the active cellular participation in the process of initial hydroxyapatite crystal formation typical of matrix vesicles, it is important to note that the same mechanisms of membrane-mediated mineral deposition appear to occur. Matrix vesicles are able to support hydroxyapatite formation in vitro. In the matrix, released crystals adhere to each other and serve as foci for continued crystal deposition. Calcospheritic structures result, completing the first stage of primary mineralization.
