Boundary cells between longitudinal and circular layers: essential for electrical slow waves in cat intestine

Abstract

Electrical slow waves were recorded by intracellular electrodes and by quasi-intracellular pressure and suction electrodes from muscle fibers at different levels in edgewise preparations of cat jejunum. Simultaneous recordings from longitudinal and circular muscle layers showed similar resting potentials from either muscle layer near the boundary zone, and lower resting potentials in cells of circular muscle near the submucosa. Slow waves were maximal in amplitude at the boundary between the two layers and spread electrotonically away from the boundary in both layers. Bipolar recordings were of opposite polarity on the two sides of the boundary. Amplitudes of slow waves from inner circular fibers were significantly lower than from outer circular fibers. Small strips of each muscle layer were prepared with or without the attached interstitial cells of Cajal plexus as identified by methylene blue staining. Either muscle layer showed slow waves from regions where interstitial cells of Cajal (ICC) were observed after the recording. No slow waves were recorded from either layer from regions where ICC were not observed. Strips containing ICC but not strips lacking ICC could be driven electrically. Since blocking of neurons does not abolish slow waves and since regions of muscle lacking ICC do not have slow waves, it is concluded that the interstitial cells (ICC-I) are most likely the boundary elements essential for slow waves in either layer of intestinal muscle.

Identification of rhythmically active cells in guinea‐pig stomach

“…In summary our observations provide a clear indication that myogenic activity results from the interaction between ICC and neighbouring smooth muscle cells (Sanders, 1996). As the ICC, from which recordings were made, appeared to be those lying in the myenteric region, the observations are consistent with the idea that, in the antrum of the stomach and in regions of the small intestine, myogenic activity is initiated at or near the junction between the longitudinal and circular muscle layer (Taylor et al 1975;Bauer et al 1985;Suzuki et al 1986). …”

A major role for carbon monoxide as an endogenous hyperpolarizing factor in the gastrointestinal tract

“…In the gastrointestinal tract these cells are interstitial cells of Cajal, specialized cells of mesenchymal origin that are required for normal intestinal motility. The main roles for interstitial cells of Cajal are thought to be to generate an electrical signal that paces intestinal smooth muscle (13,20,21,28) and to modulate enteric neurotransmission (29). Our data suggest that an additional role for interstitial cells of Cajal is to generate CO and hyperpolarize intestinal smooth muscle.…”

Are interstitial cells of Cajal plurifunction cells in the gut?

“…The physical separation of the myenteric plexus in the stomach and the small intestine, or that of the submucosal plexus in the colon, abolishes or disorganizes the slow waves in the remaining circular smooth muscle cells (8,36,96,124,143,151,159). Taken together, the findings in these studies and those in the mutant animals suggest that the potential role of the ICC-MY in the stomach and the small intestine and of ICC-SM in the colon may be to stabilize the slow waves generated spontaneously in the circular muscle cells, rather than to pace them.…”

“…3) Several studies during the 1960s and later found that the separation of the longitudinal muscle layer from the small intestine suppresses the slow-wave activity in the remaining circular smooth muscle cells (34,35,124,159). Initially, this finding had led to the conclusion that the longitudinal smooth muscle cells generate and propagate slow waves, and they also drive the slow waves in the circular smooth muscle cells.…”