Malik A B, Lynch J J, Cooper J A
Department of Physiology, Albany Medical College of Union University, New York 12208.
J Invest Dermatol. 1989 Aug;93(2 Suppl):62S-67S. doi: 10.1111/1523-1747.ep12581072.
The endothelial barrier in all organ beds allows the free exchange of water, but is restrictive to varying degrees to the transport of solutes such as albumin. For example, in the brain microvessels, the endothelial barrier restricts the transport of protein, whereas in fenestrated and continuous endothelial cells of the renal and lung endothelial cells, the endothelial barrier is semipermeable. The endothelial monolayer demonstrates selectivity, i.e., the permeation of molecules is inversely related to the molecular weight. Although the "pore" theory has been used to describe the transport across the endothelial barrier, the transport of solutes is also dependent on the charge of solutes and the endothelial cell, and the ability of the solute to bind to or be taken up by endothelial cells. Receptor-mediated trancytosis of albumin may contribute to albumin transport in addition to transport by paracellular pathways (i.e., through a so-called pore). Water permeability across the endothelium is determined by the interaction of albumin with glycocalyx and interstitial components of the endothelium (the "fiber matrix"). Ambient concentration of albumin serves to lower endothelial hydraulic conductivity. Increased endothelial permeability to solutes and water in inflammatory states is dependent on the shape and configuration of endothelial cells as determined by alterations in cytoskeletal elements, such as f-actin, and as regulated by intracellular second messengers such as free cytosolic calcium.
所有器官床中的内皮屏障允许水自由交换，但对白蛋白等溶质的运输在不同程度上具有限制性。例如，在脑微血管中，内皮屏障限制蛋白质的运输，而在肾和肺内皮细胞的有孔和连续内皮细胞中，内皮屏障是半透性的。内皮单层具有选择性，即分子的渗透与分子量成反比。尽管“孔隙”理论已被用于描述跨内皮屏障的运输，但溶质的运输也取决于溶质和内皮细胞的电荷，以及溶质与内皮细胞结合或被其摄取的能力。除了通过细胞旁途径（即通过所谓的孔隙）运输外，受体介导的白蛋白转胞吞作用可能有助于白蛋白的运输。跨内皮的水通透性由白蛋白与内皮糖萼和内皮间质成分（“纤维基质”）的相互作用决定。白蛋白的环境浓度有助于降低内皮水力传导率。炎症状态下内皮对溶质和水的通透性增加取决于内皮细胞的形状和结构，这由细胞骨架成分（如f-肌动蛋白）的改变决定，并受细胞内第二信使（如游离胞质钙）的调节。
