Junctional complex revisited by high-resolution scanning electron microscopy

The present study correlates the ultrastructural morphology of junctional complexes as revealed by transmission electron microscopy (TEM) with that observed by high-resolution scanning electron microscopy (HRSEM), thanks to a new modification of the osmium tetroxide maceration technique. The removal of all cytoplasmic organelles by this technique allows the inspection of the inner side of the plasmalemma. With this treatment, a continuous band of tightly packed particles is observed at the most apical portion of lateral membranes. Just below this band, irregular clusters of apparently identical particles are placed all around the cellular contour. The topographical correspondence among these clusters and spot desmosomes seen by TEM identifies them as desmosomes. The continuous band seems to represent the combination of both zonulae, occludens and adherens. Regarding the nature of the particles, we suppose that they probably consist of peripheral membrane proteins clustered at the cytoplasmic surface of intercellular junctions and involved in the linkage between cytoskeleton and plasmalemma.