The ultrastructural histochemistry of the basement membranes of the exocrine pancreas.

The basement membranes in the exocrine pancreas were examined by routine electron microscopy, by fixation for electron microscopy with a glutaraldehyde-tannic acid solution and by staining for ultrastructural demonstration of mucosubstances with the dialyzed iron, high iron diamine, ruthenium red and Concanavalin A-horseradish peroxidase procedures. The basement membranes are considered from morphologic and histochemical observations to consist of an inner lamina lucida, an intermediate lamina densa and an outer lamina diffusa. Sulfated mucosubstance was found in the lamina diffusa of the basement membrane of all epithelial cells and capillary endothelial cells but was encountered in the lamina lucida of the duct cells exclusively. Bridging structures, presumably polypeptides, were also seen connecting the lamina densa and the basal plasma membrane in specimens fixed with the glutaraldehydetannic acid solution. The findings demonstrated that the histochemical and morphological qualities of the basement membrane are uniform of a given cell type but differ considerably among the several cell types in the pancreas.