During leukocyte rolling on the endothelium, membrane tethers can be extracted simultaneously from both leukocytes and endothelial cells. Tether extraction, which has been shown to stabilize leukocyte rolling, is preceded by surface protrusion, which dictates whether tether extraction can occur. Although surface protrusion of leukocytes has been characterized, surface protrusion of endothelial cells has not. In this work, we present a detailed study of surface protrusion of human umbilical vein

more »

... endothelial cells (HUVECs). Using the micropipette aspiration technique, we measured the protrusional stiffness and the crossover force during HUVEC surface protrusion. We found that, compared with leukocytes, the protrusional stiffness and the crossover force of HUVECs were both larger at similar force loading rates. The values of these two parameters depended on temperature, the cytoskeletal integrity, a-actinin1, and whether CD31 or CD29 was used as the force handle. However, they did not depend on cell attachment state or intracellular calcium. These results show that similar mechanisms govern surface protrusion, hence also tether extraction in leukocytes and endothelial cells. They will help us understand and eventually control this critical step of the immune response.