Distribution of actin microfilaments and vimentin intermediate filaments in the endothelial cells, and fibronectin fibrils in the subendothelial matrix were examined using 12-day old chick embryonic arteries including the flow-divider area at branching sites.
The immunofluorescence microscopy combined with en face preparation methods and electron microscopy were used in this study. In the major straight segment of arteries where the straight laminar flow might be present, endothelial cells largely elongated along the blood flow direction and expressed the stress fibers. Cells located at just downstream of the flow-divider showed cobble stone like shape and contained an actin microfilaments layer at the cellcell boundary region without or with a few stress fiber expression. Staining with anti-vimentin showed that vimentin filament bundles in the elongated cells were roughly arranged in parallel to the major cell axis, whereas in the round cells, vimentin filaments made a thin network in the cytoplasm and formed the prominent perinuclear rings. Fbbronectin fibrils in the subendothelial matrix under the stress fiber containing cells were axially arranged parallel to the major cell axis, but those in the matrix below the round cells showed a network-like organizational pattern. Our results indicate that the endothelial cells may change their shape in response to blood flow condition, which is typically observed in the endothelium at flow divider area where the turbulent flow is suggested to be produced by the divided blood stream. Actin microfilaments and vimentin filaments in the endothelial cells, and fibronectin fibrils in the matrix showed the cell shape-dependent arranging pattern, suggesting the cell shape or blood flow direction may influence the organization of these structural elements.
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