Ultrastructural features and localization of the interstitial cells of Cajal in the smooth muscle coat of human esophagus.

The ultrastructure of the smooth muscle coat of the human esophagus has been studied. Special attention has been given to the interstitial cells of Cajal (ICC). The ICC are present wherever the esophageal musculature contains smooth muscle cells, but the amount of ICC varies with the esophageal level: in fact, the ICC are abundant in the esophageal body, are even more numerous in the lower esophageal sphincter (LES) and very rare in the gastric (distal) portion of the LES. Both the muscle layers contain ICC and their location varies according to the muscular bundles. Some ICC are inside these muscular bundles, a few are found in their proximity and the majority are located at the periphery of the bundles. According to their location, the ICC differ from one another in the extent of smooth endoplasmic reticulum, number of thin cytoplasmic filaments, presence of cytoplasmic crystalline inclusions, development of cell lateral branches and aspect of the connective tissue envelope. A great density of nerve endings, containing different types of synaptic vesicles, are preferentially related to the ICC. The inter-relationships observed between ICC, between ICC and smooth muscle cells and between ICC and Schwann cells are discussed. A structural model of the muscular bundles organization in the human esophagus is proposed and the possible role played by the ICC in the motility of the human esophagus is discussed on the basis of these morphological findings and data reported in the literature.