PMC

Ultrastructural characteristics of ICC. A: ICC-IM (ICC) in the rat stomach circular muscle layer have an electron-dense cytoplasm, many mitochondria and endoplasmic reticulum. Nerve terminals (N) are in close contact with ICC-IM. S shows smooth muscle cells in the circular layer. B: ICC-DMP (ICC) in the rat jejunum have caveolae, many mitochondria and well developed Golgi apparatus and endoplasmic reticulum. Nerve fiber bundles (N) are in close contact with ICC-DMP. S shows smooth muscle cell in the circular layer. C: ICC-MY (ICC) in the rat jejunum have caveolae, many mitochondria and well developed Golgi apparatus and endoplasmic reticulum. Myenteric ganglion (M) is located near ICC-MY. S shows smooth muscle cells in the circular layer. Bars=1 µm.

Overview of the types of ICC in the gastrointestinal tract. A–C: Schematic representations of ICC in the stomach (A), small intestine (B) and colon (C). ICC-MY (blue) are located between circular (CM) and longitudinal (LM) muscle layers. ICC-IM (red) and ICC-DMP (red) are located within circular and longitudinal muscles. ICC-SM (green) are located at the submucosal surface of the circular muscle layer in the colon. D–J: ICC and nerve networks in the murine stomach (D, E), small intestine (F, G) and colon (H–J). ICC and nerves in whole mount preparations are demonstrated by immunohistochemistry for Kit (ICC marker, green) and PGP9.5 (pan-neuronal marker, red), respectively. ICC-MY with a multipolar shape are associated with myenteric ganglia (Auerbach’s ganglia) (MG). ICC-IM in the stomach and colon have a bipolar shape and are associated with intramuscular nerve fibers. ICC-DMP in the small intestine are associated with deep muscular plexus. ICC-SM are multipolar cells having many thin processes. Bar=100 µm.

Neurokinin 1 receptor (NK1R) internalization of ICC-DMP in the murine small intestine. A, B: ICC-DMP expressing NK1R (green) are in close contact with substance P (red) containing nerve terminals (arrows). CM and LM indicate circular muscle and longitudinal muscle layers, respectively. C: Experimental scheme of electrical field stimulation (EFS). Musculature between the parallel platinum electrodes is stimulated by EFS (10 Hz, 0.5 ms duration, 15V) for 1 min. Stimulated nerve terminals release neurotransmitters such as substance P. ICC-DMP near the nerve terminals receive substance P and substance P-NK1R complexes are internalized into the cell bodies. D, E: NK1R (green) distribution in ICC-DMP before and after nerve stimulation. Before stimulation (D), NK1R are distributed around the peripheries of ICC-DMP. After EFS (E), NK1R are concentrated into granular structures (arrowheads) in ICC-DMP. Bars=20 µm (A, D, E), 50 µm (B).

ICC are associated with nerve fibers and express receptors. A, B: ICC-IM (Kit immunoreactivity, green) in the murine fundus are associated with cholinergic nerve fibers containing VAChT (A, red) and nitrergic nerve fibers containing NOS (B, red). ICC-IM are aligned horizontally in the circular muscle layer and vertically in the longitudinal muscle layer (arrows). N shows NOS-containing nerve cell bodies in the myenteric ganglia. Whole mount preparations were imaged by confocal microscope. C–E: Neurokinin 1 receptor (NK1R) distribution in the murine small intestine. ICC-DMP (arrows in C and D) labeled with Kit antibody (green) specifically express NK1R (red) in the circular muscle layer (CM), whereas ICC-MY (arrowheads) are immunonegative for NK1R between circular and longitudinal (LM) muscle layers. Immunoelectron microscopy (E) reveals ICC-DMP (ICC) expressing NK1R and associated with nerve fibers (N) in the DMP. F–H: Muscarinic M₂ receptors (M2R) distribution in the guinea pig small intestine. M2R (green, arrows) positive cells are observed between the inner circular (asterisks) and outer circular muscles (CM) shown by actin immunoreactivity (F, red). Smooth muscle cells in the outer circular muscle also showed M2R. ICC-DMP (arrows in G) contain both M2R (green) and NK1R (red) immunoreactivity in the musculature. Immunoelectron microscopy (H) shows that M2R-immunopositive cells (ICC) are typical ICC-DMP and associated with DMP (N). Bars=50 µm (A, B, D), 20 µm (C), 10 µm (F, G), 1 µm (E, H).