Ultrastructural localization and passage of cationized‐ferritin and microperoxidase as tracers in the outward flow of rat gingival crevicular fluid

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Abstract
Cationized‐ferritin (CF, high mole wt 800 000) and microperoxidase (MP, low mole wt 1900) were used to trace the outward pathway of rat gingival crevicular fluid. Gingival blood capillaries were often located near the junctional epithelium (JE). Especially, some capillaries at the coronal end of the JE protruded close to the gingival crevice. CF or MP was transuded from the capillaries and penetrated into the JE after passing through the basement lamina densa (BLD) of the external basement lamina. However, the tracer was partially blocked by the BLD. There was almost no difference between the two tracers in their ability to penetrate into the JE. Thus, the penetration of the tracer into the JE seems to be associated with the components of the BLD such as CF‐binding poly‐anionic sites or MP‐preferential affinity sites independently of the molecular weight and molecular size of the tracer. Once the tracer penetrated into the JE, it entered the gingival crevice through the intercellular spaces of the JE and along the internal basement lamina, because the cell junctions of the JE were leaky. In addition, part of the tracer was taken up by the JE. These findings suggest that only the BLD functions as a rough permeability barrier, and that most cell junctions of the JE are relatively permeable. Therefore, even high molecular weight (800 000) substances readily pass from the gingival capillaries to the gingival crevice. On their way to the crevice, exogenous materials in the fluid are phagocytosed by the junctional epithelial cells.