Electron microscopy of horseradish peroxidase uptake by papillary cells of the mouse incisor enamel organ

Abstract

Horseradish peroxidase was injected into the tail veins of adult mice. Enamel organs were excised from mice killed at predetermined intervals, fixed in formaldehyde-glutaraldehyde, incubated in diaminobenzidine medium, post-fixed in OsO 4, and processed for electron microscopy. Within 5 min of peroxidase administration, the reaction product was seen extracellularly between papillary cells and between reduced ameloblasts, but not beyond the apical terminal bar apparatus. Only papillary cells took up the peroxidase intracellularly via bristle-coated vesicles. Within the papillary cells, peroxidase was also seen in tubular structures, and at 30–60 min intervals in numerous multivesicular bodies. The results demonstrate that (1) the basal terminal bar apparatus of reduced ameloblasts is permeable to peroxidase, whereas the apical is not, (2) papillary cells function in the absorption of protein from the capillaries, and (3) bristle-coated vesicles and tubular structures serve to transport absorbed protein to multivesicular bodies within papillary cells.