Communicating-occluding junction complexes in the alveolar epithelium. A freeze-fracture study

Because studies differ as to the presence of communicating (gap) junctions in the alveolar epithelium, lung tissue from several mammalian species (man, dog, rabbit, rat, and mouse) was studied with the freeze-fracture method to clarify this problem. Communicating junctions were found between pneumonocytes in each species examined. They were always located within the meshes of or closely attached to the occluding junctions, forming communicating-occluding junction complexes. It is assumed that the communicating junctions between pneumonocytes serve mainly for metabolic coupling. The particular location of communicating junctions within the meshes of the occluding junction may be related to an additional mechanical function.