Blood flow and vascular endothelial cell function.

Vascular endothelial cells (ECs) are not merely a selective permeability barrier between blood and underlying tissue but actively play an important role in maintaining homeostasis of circulation. ECs that have a variety of synthetic, metabolic, secretory and self-adaptive capabilities regulate vascular tonus and interact with other cells such as vascular smooth muscle cells and white cells. Recent evidence suggests that these functions are affected by shear stress on the endothelial wall, which is a rheological force shearing the luminal surface of the blood vessel when a viscous fluid such as blood flows over it. Wall shear stress reportedly regulates adaptive vessel growth and angiogenesis, and might be a local risk factor in the pathogenesis of atherosclerosis. Shear stress also modulates the production of vasoactive substances such as endothelium-derived relaxing factor, prostacyclin, histamine and endothelin, and regulates macromolecule permeability and endocytosis. More recent studies have shown that shear stress exerts an influence on the expression of mRNA such as tissue plasminogen activator mRNA. These facts suggest that ECs serve as mechanoreceptors by which changes in blood flow or shear stress are recognized by the EC and the signal is transmitted to intracellular organelles. It has been indicated so far that intracellular Ca2+ and the membrane potential might be involved in the shear stress-sensing mechanism of ECs. Knowledge of EC biomechanics, i.e. the EC response to shear stress, will help us to understand the mechanism not only of blood flow-dependent vessel growth and remodeling but also atherogenesis.