Ultrastructural and cytochemical studies of resorptive and digestive functions of secretory ameloblasts in kitten tooth germs.

Ultrastructural and cytochemical studies of kitten secretory ameloblasts were made in order to clarify their functions in the resorption and digestion of extracellular organic materials. The secretory ameloblast had triangular Tomes' processes whose profile was divided into type 1 and type 2 faces. Type 1 face was associated with tubular structures, coated pits, coated vesicles, and irregularly shaped vesicles presumably representing phagosomes. Freeze-fracture replicas clearly showed the presence of large, particle-rich depressions and small depressions on the cell membrane P face in the type 1 face of the Tomes' process. Exocytosis of secretory granules was seldom observed. In both thin sections and replicas, the type 2 face possessed cell membrane microinvaginations. From the supranuclear region to a zone near the Tomes' process, many dense bodies, multivesicular bodies, and vacuoles were present; and many of them showed intense acid phosphatase reactions. Reaction products of acid phosphatase were demonstrated in the Golgi apparatus, GERL, and the lateral cell membrane. These results suggest that kitten secretory ameloblasts resorb and digest extracellular organic materials.