Data on the cytoskeleton of epithelioid cells in arteriovenous anastomosis (AVA) are sparse, but there is evidence that the (myo)-epithelioid cells of the AVAs represent a specialized smooth muscle cell type with less contractile properties. We demonstrated the expression of alpha-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 techniques and immunoelectron microscopy. Epithelioid cells in rabbit ear did 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 cells examined showed only a weak expression of the
protein smoothelin, which occurs exclusively in contractile smooth muscle cells. Immunoelectron microscopical demonstration of (alpha-smooth muscle actin revealed a striking difference in the arrangement of actin filaments in the epithelioid cells as compared to that in the smooth muscle cells of blood vessels. The epithelioid cells contained a loose array of actin filaments, whereas the smooth muscle cells contained tightly packed parallel actin bundles. In the present study we observed a correlation between the lack of contractile marker
protein expression in epithelioid cells and the presence of only a few filaments, although the epithelioid cells are alpha-smooth muscle actin positive. The reduced number of contractile elements in the epithelioid cells of rabbit and human anastomoses suggests a lower contractility of epithelioid cells compared to that of the surrounding smooth muscle cells in anastomoses. A second interesting difference between both cell types is the high number of caveolae in epithelioid cells. Immunoelectron microscopy showed a compact distribution of caveolae at the epithelioid cell border, but a more dispersed distribution of caveolae in the cytoplasm of the blood vessel endothelium. The benign
glomus tumor was characterized by an expression pattern of
cytoskeletal proteins similar to that of epithelioid cells, confirming its description as a benign
tumor.