Ultrastructural Study on Transitional Zone of Esophageal Skeleto-Smooth Muscle in Rodents

Kim, Young Ki; Nam, Kwang Il; Park, Sung Sik

Abstract

The tunica muscularis of the esophagus of rodents is entirely striated and changes to smooth muscle near the esophago-gastric junction (EGJ). The changing pattern of two types of muscles, however, have not been defined. And the existence of an anatomical sphincter at the EGJ is still a matter of uncertainty. The present study was undertaken to describe the changing pattern of skeleto-smooth muscles and to verify whether anatomical sphincter exists at EGJ in the rat and mongolian gerbil. By light microscopy, with H-E and PTAH stains, the muscle fibers consisting muscularis externa of the esophagus were entirely striated both in rat and mongolian gerbil, and abruptly changes to smooth muscle in the EGJ. A demarcation line between two types is relatively clear, but small fibers were intermingled with each other. The increase in thickness of the circular muscle layer near the EGJ was not found. Immunocytochemistry revealed that desmin was strongly positive in striated muscle fiber and positive different intensities from fiber to fiber in smooth muscle. Vimentin immuno-reactivity, however, was negative both in striated and smooth muscle. There was no racial differences in desmin and vimentin immunohisto-chemistries. By electron microscopy, there were several patterns in skeleto-smooth muscle transition: most of skeletal muscle was clearly demarcated with smooth muscle by interstitial cell and connective tissue; the skeletal and smooth muscle fibers were arranged parallel. The skeletal muscle fiber was separated from the smooth muscle fiber by long slender process of intersitial cell; the skeletal muscle fiber was interposed into wedge shaped branching smooth muscle fiber, or reverse. The typical neuro-muscular junction was found in the skeletal muscle. Smooth muscle fiber contacted with nerve varicosities and the process of interstitial cell. The smooth muscle fibers below the EGJ contracted and appeared irregular in outline. These results show the changing pattern of skeleto-smooth muscle fibers in muscularis externa of the esophagus of rodents, and suggest that the anatomical sphincter may be present at the EGJ.