FINE-STRUCTURAL STUDY OF INTERSTITIAL-CELLS ASSOCIATED WITH THE DEEP MUSCULAR PLEXUS OF THE RAT SMALL-INTESTINE, WITH SPECIAL REFERENCE TO THE INTESTINAL PACEMAKER CELLS

Two types of interstitial cells have been demonstrated in close associ ation in the deep muscular plexus of rat small intestine, by electron microscopy. Cells of the first type are characterized by a fibroblasti c ultrastructure, i.e. a well-developed granular endoplasmic reticulum , Golgi apparatus and absence of the basal lamina. They form a few sma ll gap junctions with the circular muscle cells and show close contact with axon terminals containing many synaptic vesicles. They may play a role in conducting electrical signals in the muscle tissue. Cells of the second type are characterized by many large gap junctions that in terconnect with each other and with the circular muscle cells. Their c ytoplasm is rich in cell organells, including mitochondria, granular e ndoplasmic reticulum and Golgi apparatus. They show some resemblance t o the smooth muscle cells and have an incomplete basal lamina, caveola e and subsurface cisterns. However, they do not contain an organized c ontractile apparatus, although many intermediate filaments are present in their processes. They also show close contacts with axon terminals containing synaptic vesicles. These gap-junction-rich cells may be re gular components of the intestinal tract and may be involved in the pa cemaking activity of intestinal movement.