Lectin cytochemistry on the stratum intermedium and the papillary layer in the rat incisor enamel organ.

Lectin cytochemistry was carried out to elucidate the role of stratum intermedium cells and papillary layer cells in amelogenesis, especially in the process of sugar incorporation and on membrane characteristics according to their cytodifferentiation. Regarding the lectin-reaction on the plasma membrane, little or at best a weak reaction of Con A, UEA-I, PNA, MPA and WGA was seen in stratum intermedium cells from the late differentiation stage to the early secretory stage of ameloblasts. Lectin-stainability in the stratum intermedium increased in accordance with the cytodifferentiation of ameloblasts. At the active secretory stage of ameloblasts, lectins intensely stained the plasma membranes of stratum intermedium cells. The plasma membranes of papillary layer cells at both stages of ruffle-ended and smooth-ended ameloblasts were stained by same lectins as well. The results therefore suggest that: 1) stratum intermedium cells bring about changes in the glycolipids and glycoproteins of their plasma membranes in accordance with the cytodifferentiation of ameloblasts; 2) they regulate the transport of mineral and/or organic materials between ameloblasts and extracellular fluid via highly charged plasma membranes generated by glycocalyx; 3) the cell-cell interaction of stratum intermedium cells with ameloblasts, in which carbohydrate-protein (endogenous lectin) interaction plays a significant role, is important for the cytodifferentiation of these cells. Regarding the papillary layer cells, the results suggest that they also regulate the transport of minerals by their charged plasma membranes and participate in the removal of the enamel matrix.