Summary
Odontoblasts, osteoblasts and fibroblasts of young rats were examined in the electron microscope after staining thin sections either with lead citrate alone or with uranyl acetate prior to lead citrate.
With lead citrate alone, collagen fibrils in the extracellular matrix stand out as lucent structures against a moderately electron dense background. Within the cells, lucency is restricted to certain dilated portions of the Golgi saccules as well as to the secretory granules located nearby and in the secretory pole of the cells. The lucency present in these compartments may be attributed to “fibrils” that are similar to the lucent collagen fibrils in the extracellular matrix. Other cellular compartments, e.g. the rough ER, do not display lucency.
When preparations are stained with uranyl acetate prior to lead citrate, lucency is observed neither in the matrix nor in the cells. In the matrix, collagen fibrils are easily identifiable by their cross banded pattern. In the odontoblasts, dilated portions of Golgi saccules between the outer and inner face contain filaments aligned in parallel that are approximately 3 000 Å in length. In saccules on the inner face filament aggregates are present, some of them exhibiting a cross banding pattern. In secretory granules, however, the contents appear rather homogeneous.
It is suggested that filament aggregates of collagen can assemble in the Golgi apparatus from filamentous units. These are transported through the cell by way of secretion granules and are discharged to the extracellular matrix by exocytosis.
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This investigation was supported by grants of the Medical Research Council of Canada. The author wishes to express appreciation to Dr. C. P. Leblond for his guidance in the course of this work.
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Weinstock, M. Collagen formation — observations on its intracellular packaging and transport. Z.Zellforsch 129, 455–470 (1972). https://doi.org/10.1007/BF00316743
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DOI: https://doi.org/10.1007/BF00316743