Effects of derection and pulsatility of flow on morphology and functions of cultured endothelial cells

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Effects of flow direction on shape and cytoskeletal structure of cultured bovine aortic endothelial cells were studied. Fully confluent endothelial cells cultured on glass were subjected to fluid-imposed shear stress of 20 dyne/cm^2 for 24 hours using a parallel plate flow chamber which has a low section 0.5 mm in height and 60 mm in width. Experiments on shear flow exposure were performed for (i) one-way flow, and (ii) reciprocating flow with a 30 minute interval. In the reciprocating flow experiment, medium flow was alternatively changed in the oposite direction by a roller pump and pinch valves controlled with a timer. After the flow exposure endothelial cells were fixed and Ff-actin filaments were stained with rhodamine phalloidin. Endothelial cells were observed and photographed by means of a microscope equipped with epiflluorescence optics, and the shape index of each individual cell was measured on the printed photomicrographs. Cells aligned with the flow direction and stress fibers were observed to be developed under the both flow conditions. The degrees of cell alignment under the one-way flow conditon became higher than those under reciprocating flow. Shape index value of endothelial cells exposed to the reciprocating flow (0.68(〕SY.+-.〔)0.12) was between that of the no-flow (0.87(〕SY.+-.〔)0.06)and the one-way flow conditions (0.48(〕SY.+-.〔)0.15). Dense peripheral bands of F-actin filaments were characteristically formed in honeycomb shape in the statically cultured cells. Under the one-way flow conditions, stress fibers were mainly formed in the central area of the cells and aligned with the flow direction. And the F-actin filaments around the upstream side of each cell were observed to be strongly stained. In contrast, F-actin filaments in the cells exposed to reciprocating flow almost stained homogeneously. Endothelial cells are well known to respond to shear stress. Furthermore, in conclusion, our experimental results show that endothelial cell