Interstitial cells of Cajal are innervated by nitrergic nerves and express nitric oxide-sensitive guanylate cyclase in the guinea-pig gastrointestinal tract

Nitric oxide (NO) is a major signaling molecule in the gastrointestinal tract, and released NO inhibits muscular contraction. The actions of NO are mediated by stimulation of soluble guanylate cyclase (sGC, NO-sensitive GC) and a subsequent increase in cGMP concentration. To elucidate NO targets in the gastrointestinal musculature, we investigated the immunohistochemical localization of the beta 1 and alpha 1 sub-units of sGC and the distribution of neuronal NO synthase (nNOS)-containing nerves in the guinea-pig gastrointestinal tract. Distinct immunoreactivity for sGC beta 1 and sGC alpha 1 was observed in the interstitial cells of Cajal (ICC), fibroblast-like cells (FLC) and enteric neurons in the musculature. Double immunohistochemistry using anti-c-Kit antibody and anti-sGC beta 1 antibody revealed sGC beta 1 immunoreactivity in almost all intramuscular ICC throughout the entire gastrointestinal tract. Immunoelectron microscopy revealed that sGC beta 1-immunopositive cells possessed some of the criteria for intramuscular ICC: presence of caveolae; frequently associated with nerve bundles; and close contact with smooth muscle cells. sGC beta 1-immunopositive ICC were closely apposed to nNOS-containing nerve fibers in the muscle layers. Immunohistochemical and immunoelectron microscopical observations revealed that FLC in the musculature also showed sGC beta 1 immunoreactivity. FLC were often associated with nNOS-immunopositive nerve fibers. In the myenteric layer, almost all myenteric ganglia contained nNOS-immunopositive nerve cells and were surrounded by myenteric ICC and FLC. Myenteric ICC in the large intestine and FLC in the entire gastrointestinal tract showed sGC beta 1 immunoreactivity in the myenteric layer. Smooth muscle cells in the stomach and colon showed weak sGC beta 1 immunoreactivity, and those in the muscularis mucosae and vasculature also showed evident immunoreactivity. These data suggest that ICC are primary targets for NO released from nNOS-containing enteric neurons, and that some NO signals are received by FLC and smooth muscle cells in the gastrointestinal tract. (C) 2008 IBRO. Published by Elsevier Ltd. All rights reserved.