Mechanism of controlling blood-cell passage between the sinus endothelial cells

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The fine structure of the tight junctions between the rat sinus endothelial cells was examined using freeze-fracture, triton extraction, and lanthanum-tracer techniques. In freeze-fracture replicas, the segmented strands and grooves of the tight junctions were frequently observed on the basolateral surfaces of the sinus endothelial cells. Some strands or grooves were discontinuous and were not closed. In the vertical sections of the sinus endothelial cells treated with lanthanum nitrate, most of them were situated on the basal part of the lateral surfaces of the adjacent endothelial cells. The intercellular spaces of the adjacent endothelial cells except for the fusion of the junctional membranes, were electron dense and the infiltration of lanthanum nitrate was found not to be interrupted by these tight junctions.The existence of the surface connected canalicular system (SCCS) in the sinus endothelial cells has been demonstrated by transmission electron microscopy using lanthanum nitr … More ate and, the three dimensional arrangement of the canaliculi was also demonstrated by computer-aided reconstruction. The SCCS of the sinus endothelial cells consisted of slender canaliculi which were branched, anastomosed, and showed continuity with the plasma membrane. From a computer-aided reconstruction the canaliculi, which were invaginated from various sites of the plasma membrane, were found to be continuous with each other and penetrate the sinus endothelial cell, to form a complex network in the cytoplasm.The immunolocalization of caveolin-3 in the sinus endothelial cells was examined with confocal laser scanning and electron microscopes. In immunofluorescence microscopy of the sinus endothelial cells, the contours of the endothelial cells were labelled with anti-caveolin-3. Caveolin-3 was present near stress fibers in the cytoplasm of the endothelial cells in a speckled pattern. Immunogold electron microscopy of ultrathin cryosections revealed anti-caveolin-3 labeling in caveolae in the apical, lateral, and basal plasma membranes and some vesicular profiles in the cytoplasm of the sinus endothelial cells. Less