Response of Smooth Muscle from Proximal and Distal Human Colon

Regional differences in colonic motility may be responsible for the orderly transit of intraluminal contents through the colon. The aims of this study were to compare the effect of stretch on active and passive stress development in colonic muscle from the proximal and distal colon and to compare the responses of these tissues to KC1 or bethanechol stimulation. Strips of taenia or circular smooth muscle were obtained from the disease-free segment of the colon removed for adenocarcinoma. Passive, active, and total isometric stress were measured on full-thickness strips of circular or longitudinal taenial muscle stimulated with bethanechol (10−4 M) as the muscles were stretched to 120% of the length of optimum tension (Lo.) The tissues then were stimulated with increasing concentrations of KCI and bethanechol while being stretched at Lo. The active stress in the proximal circular muscle was greater at all levels of stretch than in distal circular or longitudinal muscle (p <.001). The resting and passive stress were greater in distal circular and longitudinal taenial muscle than in proximal circular muscle (p < .05). There was a dose-dependent increase in stress development to bethanechol and KCl in each type of muscle. Proximal circular muscle had the greatest response. The EDSO was shifted to the right in distal circular muscle (2.6 ± 0.1 × 10−5 M) compared to proximal circular muscle (1.1 ± 0.1 × 10−5 M) (p < .001). These studies suggest that muscle stress differs in different locations of the colon and the role of active and passive stress development must be considered in models explaining in vivo colonic motility disturbances.