Endothelio-Pericyte and Endothelio-Smooth Muscle Cell Interactions

Abstract

The ultrastructures of endothelial cells of a capillary and a large artery shown in panels A and B, respectively, provide visual evidence that the vascular endothelium is not a simple inner lining of vascular tubes but is involved in multiple functions. All compartments of the biosynthetic apparatus and secretory system are well developed. Endothelial cells possess abundant ribosomes, extended rough and smooth endoplasmic reticulum, Golgi apparatus, storage granules and multiple mitochondria, indicating a high functional cell activity. Endothelial cells not only trigger blood coagula tion (Weibel-Palade bodies, cf. Fig. 126) but also are involved in preventing intravascular clot formation. By secretion of smooth muscle cell relaxing and contraction factors, such as nitric acid and endothelin 1, respectively, endothelial cells modulate the activities of smooth muscle cells. They also are involved in the regulation of transendothelial migration of inflammatory cells and control vascular cell growth. Endothelial cells reorient in response to shear stress, a process connected with extensive remodelling of the actin cytoskeleton.