Abstract
Bone cells of calvaria from young mice were studied at the ultrastructural level. Microtubules were demonstrated in both osteoblasts and osteocytes in the cell body, but not in the cell processes. Instead, the cytoplasm of cell processes is filled with bundles of 50 to 70 Å microfilaments, running parallel to the long axis of the process. Where two cell processes meet, the cell membranes form a tight junction. These junctions are found between osteocytes, between osteocytes and osteoblasts, and between bodies of osteoblasts on the cell surface. The cell processes usually meet side-to-side, thus forming an extended tight junction. The junctions between osteoblasts are short and are believed to be spot-like. Inside the bone scarcely any extracellular space is visible. The likelihood of intracellular transport is discussed.
Résumé
Des cellules osseuses de calottes craniennes de jeunes souris sont étudiées au microscope électronique. Des microtubules sont visibles dans les ostéoblastes et les ostéocytes dans le corps cellulaire, mais non dans les prolongements de la cellule. Le cytoplasme de ces prolongements est rempli de faisceaux de microfilaments de 50 à 70 Å, parallèles à l'axe longitudinal du prolongement. Au point de rencontre de 2 prolongements, les membranes cellulaires forment une jonction étroite. Ces jonctions s'observent entre les ostéocytes, entre les ostéocytes et les ostéoblastes et entre les corps des ostéoblastes, à la surface cellulaire. Les prolongements cellulaires habituellement se rencontrent côte à côte, formant ainsi une jonction étroite étendue. Les jonctions entre ostéoblastes sont courtes et sont de type macula. A l'intérieur de l'os, peu d'espace extra-cellulaire est visible. La probabilité de transport intracellulaire est envisagée.
Zusammenfassung
Calvarien-Knochenzellen junger Mäuse wurden im ultrastrukturellen Bereich untersucht. Es wurden in den Osteoblasten und Osteocyten der Zellkörper, nicht aber der Zellfortsätze, Mikrotubuli festgestellt. Dagegen ist das Cytoplasma der Zellfortsätze mit Bündeln von Mikrofasern von 50–70 Å gefüllt, welche parallel der Längsachse der Fortsätze angeordnet sind. An den Stellen, wo zwei Fortsätze aufeinandertreffen, bilden die Zellmembrane eine feste Verbindung. Diese Verbindungen werden zwischen Osteocyten, zwischen Osteocyten und Osteoblasten und zwischen Osteoblastenkörper auf der Zelloberfläche festgestellt. Die Zellfortsätze verbinden sich im allgemeinen entlang ihren Seiten, wodurch eine lange feste Bindung entsteht. Die Verbindungen zwischen Osteoblasten sind kurz und vermutlich punktförmig. Innerhalb des Knochens ist kaum ein extracellulärer Raum sichtbar. Die Wahrscheinlichkeit des intracellulären Transportes wird diskutiert.
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Weinger, J.M., Holtrop, M.E. An ultrastructural study of bone cells: The occurrence of microtubules, microfilaments and tight junctions. Calc. Tis Res. 14, 15–29 (1974). https://doi.org/10.1007/BF02060280
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DOI: https://doi.org/10.1007/BF02060280