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

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.