SPECIAL SMOOTH-MUSCLE CELLS ALONG THE SUBMUCOSAL SURFACE OF THE GUINEA-PIG COLON WITH REFERENCE TO ITS SPONTANEOUS CONTRACTIONS

Antiperistalses occur from the flexure region of the guinea pig colon. We previously demonstrated that the circular muscle at the mesenteric border of the flexure region produced spontaneous regular contraction s and found special smooth muscle cells believed to be pacemakers alon g the submucosal surface of the circular muscle layer. In this study, we revealed bipolar- and multipolar-type special smooth muscle cells a long the submucosal surface of the muscle layer. Their slender cell pr ocesses contacted each other and formed a cellular network. Caveolae, filament structures expressing smooth muscle actin, vimentin, some des min, and basal lamina were prominent features. The special smooth musc le cells corresponded to c-Kit-immunopositive cells and so-called inte rstitial cells or interstitial cells of Cajal in other reports. Their population was larger in the flexure region and the proximal colon tha n in the distal colon. The circular muscle layer at the flexure region was thicker than in other regions. The contraction in the flexure reg ion showed the highest frequency and regularity. The dense population of special smooth muscle cells at the flexure region and thicker muscl e layer may make the mechanical contraction more regular. The antiperi stalsis from the flexure region could be explained in relation to the highest frequency of the pulsating contraction.