ABSTRACT
Interstitial cells in the deep muscular plexus (ICC-DMP) are thought to be essential for neurotransmission in the circular muscle. There is evidence for gap junctions within the ICC-DMP network and between ICC-DMP and muscle cells; however, there is no evidence for functional coupling via these gap junctions. In addition, the innervation of individual ICC-DMP has not been studied. We investigated these questions by injecting the dye Lucifer yellow into ICC-DMP of guinea-pig ileum. Nerves were labelled immunohistochemically for protein gene product 9.5. Cells were imaged by confocal microscopy. Most (79%) of the dye-injected ICC-DMP were coupled to one to five other ICC-DMP, and 86% of them were coupled to one to five circular muscle cells. Octanol effectively blocked all coupling. Incubation in pH 6.8-7.0 reduced ICC-ICC coupling to 49% and ICC-muscle coupling to 32%. In contrast, pH 7.8-7.9 increased ICC-ICC and ICC-muscle coupling to 100%. Most ICC somata (95%) and processes (60%) were in close proximity with both nerve fibres and smooth muscle cells. These results provide direct evidence for functional coupling within the ICC-DMP network, and between this network and cells of the outer circular muscle layer and showed that coupling can be affected by pH.
Subject(s)
Connective Tissue Cells/physiology , Ileum/innervation , Ileum/physiology , Animals , Connective Tissue Cells/chemistry , Guinea Pigs , Ileum/chemistry , Male , Myenteric Plexus/chemistry , Myenteric Plexus/physiology , Myocytes, Smooth Muscle/chemistry , Myocytes, Smooth Muscle/physiology , Nerve Fibers/chemistry , Nerve Fibers/physiology , Nerve Net/chemistry , Nerve Net/physiologyABSTRACT
A major difficulty in the investigation of interstitial cells of Cajal (ICC) is in identifying these cells within intact, living gastrointestinal tissues. To overcome this difficulty we developed a method to visualize ICC in the myenteric plexus region (ICC-MP) of the guinea pig ileum. Cells were identified with Nomarski optics and were injected with the fluorescent dye Lucifer yellow. The identity of the cells as ICC was verified by immunohistochemical labeling for the protein c-Kit. Using the dye coupling method we found that 24.4% (93/381) of ICC-MP were coupled to 1-21 other ICC. Octanol reduced dye coupling incidence among ICC-MP to 2% (1/49). Raising the pH in the medium to 7.8-7.9 increased the dye-coupling incidence to 86% (37/43, P<0.001). Lowering the pH to 6.4-6.8 had the opposite effect (coupling incidence 1/44). These findings demonstrate that ICC are mutually connected by channels, apparently gap junctions, that can allow the passage of both electrical currents and small molecules. As it was modulated by pH, it is likely that ICC coupling is under physiological control.
