IDENTIFICATION AND CLASSIFICATION OF INTERSTITIAL-CELLS IN THE CANINEPROXIMAL COLON BY ULTRASTRUCTURE AND IMMUNOCYTOCHEMISTRY

The ultrastructure and immunocytochemistry of interstitial cells (ICs) in the canine proximal colon were investigated. Three types of ICs we re found within the tunica muscularis. (1) ICs were located along the submucosal surface of the circular muscle (IC-SM). These cells shared many features of smooth muscle cells, including myosin thick filaments and immunoreactivity to smooth muscle gamma actin, myosin light chain , and calponin antibodies. IC-SM were clearly different from smooth mu scle cells in that contractile filaments were less abundant and interm ediate filaments consisted of vimentin instead of desmin. (2) ICs in t he region of the myenteric plexus (IC-MY) were similar to IC-SM, but t hese cells had no thick filaments or immunoreactivity to smooth muscle gamma actin or calponin antibodies. (3) The fine structures and immun oreactivity of ICs within the muscle layers (IC-BU) were similar to IC -MY, but IC-BU lacked a definite basal lamina and membrane caveolae. I C-BU and IC-MY were both immunopositive for vimentin. Since all ICs we re immunopositive for vimentin, vimentin antibodies may be a useful to ol for distinguishing between ICs and smooth muscle cells. Each class of ICs was closely associated with nerve fibers, made specialized cont acts with smooth muscle cells, and formed multicellular networks. A co mbination of ultrastructural and immunocytochemical techniques helps t he identification and classification of ICs by revealing the fine stru ctures and determining the ''chemical coding'' of each class of ICs.