CYTOSKELETAL CHARACTERIZATION OF ARTERIOVENOUS EPITHELIOID CELLS

Data on the cytoskeleton of epithelioid cells in arteriovenous anastom osis (AVA) are sparse, but there is evidence that the (myo)-epithelioi d cells of the AVAs represent a specialized smooth muscle cell type wi th less contractile properties. We demonstrated the expression of alph a-smooth muscle actin, smooth muscle myosin, calponin, caldesmon, and caveolin in epithelioid cells of rabbit ear and in human toes, finger tips, and glomus tumors by means of indirect immunofluorescence techni ques and immunoelectron microscopy. Epithelioid cells in rabbit ear di d not express vimentin, but it was present in human toes, finger tips, and glomus tumors. Epithelioid cells in human toes, finger tips, and glomus tumors did not express desmin, but it was present in rabbit ear . Epithelioid cells did not express cytokeratins. The epithelioid cell s examined showed only a weak expression of the protein smoothelin, wh ich occurs exclusively in contractile smooth muscle cells. Immunoelect ron microscopical demonstration of alpha-smooth muscle actin revealed a striking difference in the arrangement of actin filaments in the epi thelioid cells as compared to that in the smooth muscle cells of blood vessels. The epithelioid cells contained a loose array of actin filam ents, whereas the smooth muscle cells contained tightly packed paralle l actin bundles. In the present study we observed a correlation betwee n the lack of contractile marker protein expression in epithelioid cel ls and the presence of only a few filaments, although the epithelioid cells are alpha-smooth muscle actin positive. The reduced number of co ntractile elements in the epithelioid cells of rabbit and human anasto moses suggests a lower contractility of epithelioid cells compared to that of the surrounding smooth muscle cells in anastomoses. A second i nteresting difference between both cell types is the high number of ca veolae in epithelioid cells. Immunoelectron microscopy showed a compac t distribution of caveolae at the epithelioid cell border, but a more dispersed distribution of caveolae in the cytoplasm of the blood vesse l endothelium. The benign glomus tumor was characterized by an express ion pattern of cytoskeletal proteins similar to that of epithelioid ce lls, confirming its description as a benign tumor.