Electric activity spreads in the colonic longitudinal but not the circular musculature. Role in colonic motility.
The colon has a circular and longitudinal muscle layers and possesses an electric activity. The current study investigated the spread of this electric activity in the colonic musculature. The tests were performed in 16 patients (mean age 40.6 +/- 10.8 SD years, 10 men, 6 women) during operative correction of their incisional hernias in the anterior abdominal wall. Three electrodes were applied to the longitudinal muscle of the descending colon, and 3 to the circular muscle. The colonic pressure was monitored by a 10-F tube inserted per anus and connected to a pressure transducer. Electric waves in the form of pacesetter potentials (PPs) and action potentials (APs) were recorded from the longitudinal but not the circular muscle coat. The PPs and APs had the same frequency, amplitude and conduction velocity from the 3 electrodes of the same patient. The APs were associated with a rise of the intracolonic pressure. The results were reproducible in the individual subject. Being of the visceral type, the colonic smooth muscle fibers are controlled by non-nervous stimuli. Colonic motility is suggested to be effected by means of 2 mechanisms: the longitudinal muscle fibers activity through the action of the electric waves and the circular muscle fibers through the stretch reflex.