ON MEASURING THE 3RD-DIMENSION OF CULTURED ENDOTHELIAL-CELLS IN SHEAR-FLOW

The stress in the endothelial cells induced by blood flow depends on t he waviness of the blood-endothelium interface and the slopes at the j unctions of neighboring cells in the direction of flow. The height and slope in the third dimension of the living endothelial cells cannot b e measured by ordinary optical and electron microscopy. Here we show t hat interference microscopy meets the challenge. We measured the geome try of cultured confluent human vascular endothelial cells in a flow, and we found that in a normal section parallel to the flow, the absolu te values of the surface slopes at the cell junctions were 0.70 +/- 0. 02 (SE) and 0.80 +/- 0.02 (SE) at the leading and trailing edges of th e cells, respectively, in a culture medium of osmolarity 310 mosM with a shear stress of approximately 1 N/m(2). A reversal of the flow dire ction led to a reversal of the slope pattern. An increase in medium os molarity above 310 mosM induced an initial decrease in the slopes foll owed by a return to normal, whereas a decrease in the osmolarity had a reversed effect. These results, in light of our previous theoretical analyses, show that tensile stress exists in the endothelial cell memb rane, and that the mechanism of tension accumulation is a reality. The accumulation is not 100% because the membranes are not smooth at the cell junctions.