The longitudinal and circular muscle layers of canine colon showed a different pattern of mechanical activity: regular rhythmic phasic contractions in the circular strips and irregular rhythmic prolonged contractions in the longitudinal strips. 2. The spontaneous motility of both layers was suppressed by atropine (1 microM) or hexamethonium (1 microM), suggesting the involvement of ACh. 3. Somatostatin (1 nM-1 microM) decreased, while CCK8 (1-10 nM) increased the spontaneous and electrically-induced contractions of the colonic muscles, the circular layer being more sensitive as compared to the longitudinal layer. 4. CCK8 enhanced both resting and electrically-induced [3H]ACh release, while SOM inhibited the electrically-stimulated [3H]ACh release.
