Channels across Endothelial Cells
Radu V. Stan
The evolution of multicellular organisms entailed the formation of biological compartments separated by epithelial cellular barriers. As a consequence, strategies have evolved to move exchange materials between these compartments for nutrition, wastes removal and information exchange, while still maintaining their identity. These exchanges occur either across barrier cells (transcellular) or in between adjacent cells (paracellular). Among the strategies employed for transcellular exchange are the formation of physical patent channels/pores that cut through the cells and the formation of “functional channels” by shuttling vesicles during transcytosis. In this chapter, I will summarize the knowledge of the transcellular exchange systems using the vascular endothelium as a barrier model. We will focus on the components, structure and function of the endothelial organelles such as fenestrae, vesiculo-vacuolar organelles and transendothelial channels as well as the vesicular carriers involved in transcytosis (i.e., plasmalemmal vesicles or caveolae), which form either physical or functional channels across endothelial cells.