Vimentin intermediate filaments: the central base in sinus endothelial cells of the rat spleen.

The ultrastructural distribution of vimentin intermediate filaments (IFs) and localizations of the related proteins in sinus endothelial cells of the rat spleen was examined by confocal laser scanning and electron microscopy with detergent extraction, myosin-fragment 1 decoration, and immunogold labeling to elucidate their functions in endothelial cells. Vimentin IFs were extremely abundant over stress fibers in the basal part of the endothelial cells. Some of them were intermingled with actin filaments in stress fibers, and were associated with coated vesicles. Plectin was predominantly localized in the layers of vimentin and stress fibers of the endothelial cells, but rarely in the vicinity of adherens junctions in the lateral part and focal adhesions in the basal part of the cells. Neither plakoglobin nor desmoplakin, which is coupled VE-cadherin to vimentin IFs, was detected in sinus endothelial cells. Vinculin was localized in the basal membranes of the endothelial cells. These data suggest that abundant vimentin IFs are associated with stress fibers by plectin in the basal part of the cells and form cytoskeletal cores of sinus endothelial cells only partially supported by the ring-shaped basal lamina to have roles in scaffolding and the mechanical stabilization of the endothelial cells. Furthermore, taken in connection with recently revealed functions of vimentin and plectin, vimentin might play a cytoskeletal core of sinus endothelial cells.