IMMUNOELECTRON MICROSCOPIC CHARACTERIZATION OF THE EPITHELIOID TYPE OF SMOOTH-MUSCLE CELLS IN HUMAN GLOMUS ORGANS

The wall structure of arterio-venous anastomoses in human glomus organ s was studied by immunohistochemistry and immunoelectron microscopy. S mooth muscle cells of the epithelioid type I and of the dense type II could be found in the media. The immunohistochemical study confirmed t he immunopositivity of both smooth muscle cell types for alpha-smooth muscle actin, vimentin, and smooth muscle myosin. All smooth muscle ce lls also stained positively for caveolin, a recently described structu ral protein of microvesicles present in selected epithelial and nonepi thelial cells. The immunoreactivity for cathepsin D, however, was much higher in the type I cells than in the type II cells. Immunoelectron microscopy revealed that type I cells contain loose arrays of alpha sm ooth muscle actin positive microfilaments, sometimes arranged in small bundles, whereas the dense medial smooth muscle cells of the type II have tightly packed actin filaments. Only type I cells contained cathe psin D positive lysosomes. The data suggest that two types of phenotyp ic variants of vascular smooth muscle cells in the human arterio-venou s anastomosis exist: a more ''synthetic'' type I cell and a more contr actile type II cell.