LIGHT MICROSCOPIC AND ELECTRON-MICROSCOPIC STUDIES OF INTERSTITIAL-CELLS OF CAJAL AND MUSCLE-CELLS AT THE SUBMUCOSAL BORDER OF HUMAN COLON

BACKGROUND: It has been suggested that interstitial cells of Cajal (IC C) at the submucosal border of the colonic circular muscle are pacemak er cells. We studied smooth muscle cells and ICC at the submucosal sur face of the circular muscle layer of the normal human colon. EXPERIMEN TAL DESIGN: Resected, unaffected specimens from human colon were studi ed by light microscopy and transmission electron microscopy. RESULTS: Throughout the colon, the inner fourth of each circular-muscle lamella was covered with a layer of 2 to 15 muscle cells (ICMC) with a smalle r diameter, more perinuclear organelles, and a greater glycogen conten t than the outer circular muscle cells. ICMC were interconnected by ad herens junctions and close appositions. Small bundles of ICMC were pre sent in the submucosa. ICC were identified in all regions of the colon (ascendens, transversum, and sigmoideum) at the submucosal border, in deeper parts of the submucosa in close contact with smooth muscle bun dles as well as in the circular muscle and main septa. ICC had a conti nuous basal lamina, caveolae, dense bands, thin and intermediate filam ents, dense bodies and a well-developed smooth endoplasmic reticulum. Mitochondria and granular endoplasmic reticulum were very abundant. Li pid droplets and glycogen granules were frequent. Thick (myosin) filam ents were absent. Close contacts to nerves and gap junctions to other ICC or smooth muscle cells were exceptional. Fibroblast-like cells in the submucosa were rich in granular endoplasmic reticulum and intermed iate filaments. They had few dense bands and caveolae. Mitochondria, s mooth cisternae and glycogen granules were sparse, cytoplasmic dense b odies and a continuous basal lamina were lacking. Fibroblast-like cell s were associated closely with collagen bundles and they had no close contacts with nerves, ICC or muscle cells. CONCLUSIONS: Throughout the normal human colon, submucosal ICC and ICMC are identified and distin guished from other cell types present. Their organization and cytology differ from that of other animal species. The ultrastructure of ICC a nd ICMC is compatible with important regulatory functions on the circu lar muscle in the entire human colon.