EARLY MINERALIZATION OF MATRIX VESICLES IN THE EPIPHYSEAL GROWTH-PLATE

Matrix vesicles (MVs) induce the primary mineralization in collagen-ri ch hard tissue such as bone, mineralizing cartilage and dentine. Calci um and phosphate ions accumulate at the inner MV membrane. This accumu lation takes place in association with phospholipids alone and/or in a ssociation with Annexin V, which displays Ca ion channel activity when inserted in membranes; consequently, Annexin V may be involved in Ca uptake by matrix vesicles. This first crystal nuclei are formed at the se macromolecules of the MV inner membrane. They grow to stable nanome tre-sized particles, dots, which coalesce to form chains of dots alone the macromolecules of the MV inner membrane. At the same time, or sho rtly afterwards, chains of these Ca phosphate dots also develop inside the MVs. The measured centre-to-centre distances between the nucleati ng sites, called active sites, along the MV matrix molecules. The mine ralization does not stop at the MV membrane but expands continuously i nto the extra-vesicular region in radial directions to form nodules. T hese radiating Ca phosphate chains, which coalesce to form needles, ar e composed of such primary dots, which have developed at the nucleatin g sites of the corresponding macromolecules.