Peroxidase penetration in the crevicular epithelium of rat molar gingiva

Rat molar gingiva was studied by tracer experiments employing horseradish peroxidase and by cytochemical demonstration of inorganic trimetaphosphatase. Though non-keratinized junctional epithelium appeared to have no effective diffusion barrier against the permeation of peroxidase, keratinized sulcular epithelium had an evident barrier for the tracer at the junction between the granular and cornified layers. The barrier to peroxidase permeation was closely associated with the presence of either numerous membrane-coating granules or a cornified layer. The basal cells of both junctional and sulcular epithelia frequently took up peroxidase by means of coated pits, vesicles and endocytotic vacuoles. Inorganic trimetaphosphatase activity was present in dense bodies, multivesicular bodies and vacuoles, but not necessarily related closely to peroxidase incorporation within the cytoplasm.