Application of backscattered electron imaging and lectin-gold cytochemistry to visualize the distribution of glycoconjugates in a basal lamina.

Basement membranes generally appear in transmission electron microscopy as thin, cross-sectioned profiles. Face-views are difficult to obtain particularly when their contours are curved or undulated. Such preparations are suited for the study of the distribution of basement membrane constituents through thickness but are limited for examining their spatial distribution. Scanning electron microscopy offers the potential of visualizing surface views. We have applied this approach to examining the three-dimensional distribution of glycoconjugates in a basement membrane. Large, face-views of the basal lamina related to maturation ameloblasts in the region where enamel of the rat incisor is EDTA soluble were exposed. Glycoconjugates were then revealed by incubating the segments in lectin-gold complexes and binding sites were visualized by backscattered electron imaging. This basal lamina was found to contain fucose, mannose and to be extremely rich in N-acetyl-D-galactosamine. The abundance of glycoconjugates containing the latter sugar residue may impart on this basal lamina selective properties which could regulate the movement of material into, and out of, the enamel layer.