Ultrastructural and histochemical characterization of special muscle cellsin the monkey small intestine

The ultrastructure, three-dimensional arrangement, and histochemical featur es of special muscle cells in the monkey small intestine were investigated. The cells formed a special layer separated from the main part by a connect ive tissue space along the submucosal surface of the circular muscle coat. Scanning electron microscopy using alkali maceration demonstrated this inne r sublayer to he a continuous thin sheet consisting of irregularly-shaped m uscle cells equipped with many cytoplasmic projections and caveolae. Other ultrastructural features included direct contact with interstitial cells, d ue to their close association with nerve fibers of the deep muscular plexus . Histochemical examination revealed significant alkaline phosphatase activ ity and immunoreactivity for vascular smooth muscle alpha actin in these mu scle cells, whereas the ordinary circular muscle cells were immunopositive for enteric smooth muscle gamma actin. These findings suggest that the spec ial muscle cells play an important role in regulating the radial stretch of the monkey small intestinal wall.