Sulfated glycoconjugates in rat incisor secretory ameloblasts and developing enamel matrix

We investigated the ultrastructural distribution and histochemical properties of sulfated glycoconjugates, which could be preserved by glutaraldehyde fixation, in secretory ameloblasts and developing enamel matrix, by use of the high iron diamine thiocarbohydrazide silver proteinate (HID-TCH-SP) staining and enzymatic digestion methods. Large type HID-TCH-SP stain deposits, approximately 10 nm in diameter, were detected on the interdigitating cell membrane of Tomes' process, inside some secretory granules, on the lateral cell membrane of stratum intermedium, in the basement membranes associated with outer enamel epithelium and endothelial cells of capillary, within the so-called hole region, and in the enamel matrix near future enamel-cement junction. A few large type stain deposits were, however, randomly distributed over the whole layer of enamel matrix. Small type stain deposits smaller than 5 nm in diameter were localized within some secretory granules and Golgi vesicles of ameloblasts and on the surface layer of developing enamel matrix. While the large type HID-TCH-SP stain deposits associated with the basement membranes and on the lateral cell membrane of stratum intermedium were susceptible to heparitinase, the others resisted enzymatic digestion not only by heparitinase but also by testicular hyaluronidase and chondroitinase ABC, indicating that they represent sulfated glycoconjugates other than heparan sulfate, chondroitin sulfate A, dermatan sulfate, or chondroitin sulfate C. On the other hand, HID-TCH-SP stain deposits within the secretory granules of odontoblasts and in the predentine matrix were susceptible to testicular hyaluronidase. Thus, it was confirmed that the composition of sulfated glycoconjugates secreted into the developing enamel matrix differs essentially from that of sulfated glycoconjugates associated with dentinogenesis.