Stress fiber networks in sinus endothelial cells in the rat spleen

Abstract

The wall of the splenic sinus is well known to be a critical site in the control of the blood-cell passage through the splenic cord. However, there is little information on what mechanism controls the blood-cell passage between the sinus endothelial cells adhered with intercellular junctions.Stress fibers of sinus endothelial cells in the rat spleen were examined by transmission electron microscopy and immunofluorescence microscopy. After extraction with saponin, the stress fibers were found to be conspicuously electron-dense in the basal portion of the cells and demonstrated two characteristic types and the mixed type of these. One type of the stress fibers was corrugated and formed thick, electron-dense bundles, and the other type had straight bundles with electron-dense areas at intervals. Statistically, the lengths of two types of stress fibers are significantly different. Although most of the stress fibers were segmented by the ring fibers, some of them ran successively beyond the attachment site of the ring fibers and thus stretched longitudinally and tangentially in the basal part of the cell to form a widespread network. The peripheries of the networks were attached to the basal plasma membrane at the ring fibers and the lateral membranes at the focal adhesions and the cell-cell adherens junction, respectively. Phosphotyrosine is localized in the basal part and at the intercellular adhesion site of the endothelial cells.Two types of stress fibers were organized in the sinus endothelial cells, and they form a widespread network. The possibility might be considered that stress fibers play important roles in the signal transduction and the regulation of cellular attachment and detachment.

Tubular invaginations with caveolae and coated pits in the sinus endothelial cells of the rat spleen

“…1). Since the network of the stress fibers spreads in the endothelial cells (Uehara and Miyoshi 1999a), the caveolae derived from the tubular invaginations may be associated with the smooth-surfaced cisternae and the stress fibers in three dimensions. It is therefore likely that the caveolae in the sinus endothelium might play a similar role in the calcium regulation and contraction of stress fibers.…”

“…They are spindleshaped and arranged parallel to the long axis of the sinus and are bound with a fenestrated basal lamina that is shaped like barrel hoops. Furthermore, they have a highly ordered network of contractile stress fibers (Drenckhahn and Wagner 1986;Uehara and Miyoshi 1999a). In addition, they express antigens associated with T lymphocytes, monocytes, and macrophages (Buckley et al 1985) and are devoid of any detectable amounts of acidic glycoconjugates (Ueda et al 1996).…”

P2Y1, P2Y6, and P2Y12 receptors in rat splenic sinus endothelial cells: an immunohistochemical and ultrastructural study

“…In particular, their shape and arrangement are prominent, resembling the staves of a barrel, with a highly ordered network of contractile stress Wbers running longitudinally in their basal part, and fenestrated basal lamina barrel-like hoops called "ring Wbers" (Drenckhahn and Wagner 1986;Uehara and Miyoshi 1999a). Since the endothelium is devoid of smooth muscles and the endothelial cells are only attached to the ring Wbers by focal adhesion, their basal membranes except focal adhesions are exposed to the splenic cord, receiving direct mechanical stimuli from the environment at abluminal sites as well as the luminal surface.…”

Localization of TRPC1 channel in the sinus endothelial cells of rat spleen

“…Particularly prominent are their shape and arrangement, which resemble the staves of a barrel with a highly ordered network of contractile stress fibers running longitudinally in their basal part (Drenckhahn and Wanger 1986;Uehara and Miyoshi 1999a) and fenestrated basal lamina barrel-shaped hoops. Furthermore, Ca 2+ -storing tubulovesicular structures are located throughout the sinus endothelial cells in close apposition to the plasma membrane, caveolae, and stress fibers Miyoshi 1999b, 2002;Uehara et al 2004).…”