Ultrastructural characterization of interstitial cells of Cajal associated with the submucosal plexus in the proximal colon of the guinea pig

Interstitial cells of Cajal (ICC) associated with the submucosal (submucous) plexus (ICC-SP) in the proximal colon of the guinea pig were studied by immunohistochemistry and electron microscopy. Whole-mount stretch preparations with c-Kit immunohistochemistry revealed that a number of ICC-SP constituted a dense cellular network around the submucosal plexus. Some of these ICC-SP were observed in the vicinity of the muscularis mucosae in sections immunostained for c-Kit and α-smooth muscle actin. Ultrastructural observation demonstrated, for the first time, that ICC-SP of the proximal colon of the guinea pig retained typical ultrastructural characteristics of ICC repeatedly reported in association with the tunica muscularis of the gastrointestinal tract: a basal lamina, caveolae, many mitochondria, abundant intermediate filaments and the formation of gap junctions with the same type of cells. The most remarkable ultrastructural finding was the presence of thick bundles composed of the processes of ICC-SP connected to each other via large gap junctions. These ICC-SP might be involved in the main mucosal functions of the proximal colon of the guinea pig, namely the transportation of water and electrolytes, possibly via their involvement in the spontaneous contractions of the muscularis mucosae.