Coordination of electrical activities in muscle layers of the pig colon

Simultaneous recording of electrical activities from the circular and longitudinal muscle layers of the pig colon was performed in vitro to study possible coordination of activities. The electrical activity of both muscle layers consisted of electrical oscillations with superimposed spikes. The frequency range of the electrical oscillations in the circular muscle was 0.5-3.5 cycles per minute (cpm) and in the longitudinal muscle 24-42 cpm. Coordination of the activities of both muscle layers occurred consistently only after stretch or cholinergic stimulation. Then it occurred in a unique fashion. Each oscillation in the circular muscle layer occurred at the same time as the onset of a burst of oscillations in the longitudinal muscle. In addition, multiple simultaneous recordings of the electrical activities from each muscle layer were obtained showing that within the circular muscle layer electrical oscillations were phase locked in the circumferential direction and along the long axis of the colon. They appeared to propagate in either the oral or aboral direction. In tetrodotoxin (with stretch as stimulus) and also in presence of carbachol, bursts of oscillations in the longitudinal muscle layer were phase locked circumferentially (in the different taeniae) and longitudinally. This study shows that the muscle layers in the colon, which have different myogenic electrical activities, can obtain a high level of coordination.