Regional Comparison of Rat Colon Mechanics

Abstract

The purpose of this study was to examine the force‐velocity characteristics of colonie muscle and to determine whether these factors contribute to regional specialization of the colon observed in adult Fischer rats. Four measurements were obtained from circular colon muscle strips: maximum shortening velocity, a reflection of crossbridge cycling rate; extension of the parallel elastic component, a measure of passive muscle properties of relaxed muscle; the series elastic component, a measure of passive muscle properties of contracted muscle; and peak isometric force, which is equal to the product of the number of activated crossbridges and the strength of individual crossbridges. Muscle length (L) was expressed in terms of the length of optimal tension development (Lo). Peak isometric force and maximum shortening velocity were 848.9 ± 114.7 g/cm2 and 0.082 ± 0.012 Lo/s for muscle strips from the proximal colon, and 948.0± 138.2 g/cm2 and 0.083 ± 0.014 Lo/s for muscle strips from the distal colon. Shortening velocity, isometric force, and load extension properties of the parallel elastic component and the series elastic component are similar in proximal and distal rat colon. This suggests that regional specialization is not determined at the myofibril level but is most likely determined by extrinsic regulatory factors at the neural or receptor level.