Abstract
Endothelial cells (ECs) sense the hemodynamic forces, such as shear stress and stretch, and transduce blood flow information into functional responses that play important roles in vascular homeostasis and pathophysiology. A unique feature of shear-stress-sensing is the involvement of many different types of membrane-bound molecules, including receptors, ion channels, and adhesion proteins, but the mechanisms remain unknown. To determine how hemodynamic forces influence the cell membrane, cultured ECs were exposed to shear stress and examined for changes in membrane lipid order and fluidity by Laurdan two-photon imaging and FRAP measurements. Upon flow stimulation, the lipid phases of EC membranes changed from the liquid-ordered state to the liquid-disordered state in an intensity-dependent manner, and membrane fluidity increased over the entire membranes. Notably, a similar change in lipid order occurred in the artificial membranes of giant unilamellar vesicles, suggesting that this is a physical phenomenon. These findings indicate that EC membranes directly respond to shear stress by rapidly decreasing their lipid phase order and increasing their fluidity.
