Soares A M, Arana-Chavez V E, Reid A R, Katchburian E
Department of Histology and Embryology, University of São Paulo, Brazil.
J Anat. 1992 Oct;181 ( Pt 2)(Pt 2):345-56.
In adult bone the calcified matrix and enclosed osteocytes are separated from the extracellular space by a continuous layer of bone lining cells. It thus appears that bone matrix is compartmentalised and, as such, may constitute a 'milieu intérieur' which is different from the general extracellular space. Since adult bone matrix is compartmentalised and matrix vesicles also form a microcompartment, it is conceivable that compartmentalisation, in early osteogenesis, may be a requirement for the initial events of the mineralisation process. We have therefore conducted an ultrastructural, tracer, and freeze-fracture study to determine the stage in which bone matrix becomes compartmentalised and also to find out whether there are tight junctions between osteoblasts. The results show that in early nonmineralised stages and in incipient mineralisation, lanthanum penetrates all intercellular spaces and the newly forming bone matrix which is rich in matrix vesicles and collagen. With the progression of mineralisation, when all matrix vesicles appear mineralised and calcification is 'spreading' to the surrounding matrix, lanthanum is restricted to intercellular spaces and conspicuous macular tight junctions are present between osteoblasts. We suggest that matrix vesicles act as microcompartments for calcification when the early bone matrix is in continuity with the surrounding extracellular space. In later stages, when lanthanum fails to penetrate the matrix, matrix vesicles may no longer be necessary because the bone matrix itself is compartmentalised, thus allowing for localised changes in composition that might favour mineral deposition.
在成年骨骼中，钙化基质和包埋的骨细胞被一层连续的骨衬细胞与细胞外空间分隔开来。因此，骨基质似乎是分隔的，并且可能构成一个与一般细胞外空间不同的“内环境”。由于成年骨基质是分隔的，基质小泡也形成一个微区室，所以可以想象，在早期骨生成过程中，分隔可能是矿化过程初始事件的一个必要条件。因此，我们进行了一项超微结构、示踪和冷冻断裂研究，以确定骨基质开始分隔的阶段，并查明成骨细胞之间是否存在紧密连接。结果表明，在早期非矿化阶段和初始矿化阶段，镧可穿透所有细胞间隙以及富含基质小泡和胶原蛋白的新形成的骨基质。随着矿化的进展，当所有基质小泡都出现矿化且钙化“扩散”到周围基质时，镧被限制在细胞间隙，并且成骨细胞之间出现明显的斑状紧密连接。我们认为，当早期骨基质与周围细胞外空间连续时，基质小泡作为钙化的微区室。在后期，当镧无法穿透基质时，基质小泡可能不再必要，因为骨基质本身已被分隔，从而允许成分发生局部变化，这可能有利于矿物质沉积。
