CONTROL OF MOTILITY PATTERNS IN THE HUMAN COLONIC CIRCULAR MUSCLE LAYER BY PACEMAKER ACTIVITY

1.This study characterized the electrical and mechanical activities of human colonic muscle strips obtained from either the ascending, desce nding or sigmoid colon of patient volunteers during elective colon res ections. 2. Rhythmic contractile activity was observed in colonic circ ular muscle strips in the absence of external stimuli. This activity p ersisted in the presence of atropine, phentolamine, propranolol, tetro dotoxin and N-omega-nitro-L-arginine but was abolished by nifedipine. 3. The activity of whole circular muscle (WCM) was compared with that of the myrenteric half (MCM), the submucosal half (SCM) and the interi or (ICM) of the circular muscle layer. WCM exhibited a prominent 2-4 c ontractions min(-1) contractile pattern which was also present in stri ps of SCM. In contrast, MCM and ICM exhibited slow (0.3-0.6 contractio ns min(-1)), long duration contractions with superimposed higher frequ ency contractions (17-18 contractions min(-1)). 4. Resting membrane po tential (V-m), recorded at various positions through the thickness of WCM strips did not differ and averaged -50 mV. 5. Slow waves were obse rved in 83% of muscles. They averaged 12 mV in amplitude, 9.4 s in dur ation and had a frequency of 2-4 contractions min(-1). Slow waves were greatest in amplitude near the submucosal edge and decreased with dis tance away from this edge. Each slow wave was associated with a transi ent contraction. 6. Near the myenteric edge, rapid fluctuations of V-m with a mean frequency of 18 contractions min(-1) were recorded in 67% of muscles. Spiking activity was common and was superimposed upon slo w waves and rapid V-m fluctuations. 7. In summary slow was es were ide ntified in the human colonic circular muscle layer which arise at or n ear the submucosa! edge. These electrical events give rise to a 2-4 co ntractions min(-1) contractile rhythm which is characteristic of the i ntact muscle layer. Thus, the nature and spatial organization of pacem aker activity in the human colon bears significant resemblance to othe r animal models, such as the dog and pig.