The effects of vinblastine on the secretory ameloblasts: an ultrastructural, cytochemical, and immunocytochemical study in the rat incisor

Secretory ameloblasts synthesize the organic matrix of enamel and secrete it at two distinct "putative secretory sites" characterized by membrane infoldings (Nanci and Warshawsky, 1984a). The antimicrotubular agent vinblastine sulphate interferes with secretion. We have examined the effect of this drug on the ameloblast secretory sites and re-evaluated the effect on the intracellular organization of the cell by using conditions that optimize fixation, cytochemistry (ZI0), and immunocytochemistry. Associated with the disappearance of secretory granules and Golgi-related structures from Tomes' process was the loss of membrane infoldings at secretory sites. The Golgi apparatus appeared fragmented and numerous granule clusters were found throughout the cell body. These clusters were often seen in relation to extracellular patches of material in which no crystallites were seen. Immunocytochemistry revealed the presence of enamel proteins in the protein synthetic organelles, including various granule types, in lysosomes and in the extracellular patches. These data suggest that ameloblasts under the effect of vinblastine carry on secretory activities, but the product is not routed to the usual sites. It was confirmed that membrane infoldings characterize the sites where enamel proteins are normally secreted.