Regulation of endothelial transport

Sammanfattning: A major role of endothelial cells is to control the influx of solutes into tissues. The aim of the research presented in this thesis was to gain knowledge about the regulation of endothelial transport in relation to the structure of the endothelial cytoskeleton and to elucidate the possible mechanisms of regulation.The transcellular transport of hydrophilic molecules was found to occur viavesicles arranged as chains stretching between the luminal surface and the interior of the cell, and also from the cell interior to the abluminal surface. Intact microtubules were required for this transport, and actin filaments acted as a hinder. In addition, the vesicular transport was stimulated by hydrogen peroxide (H20z) and phorbol myristate acetate (PMA), and the effect of PMA was dependent on reactive oxygen species.The structure of filamentous actin and the permeability were closely associated during stimulation with H20z and PMA. An increase in actin dense peripheral bands (DPBs) was correlated with a decrease in penneability during the first hour of exposure to PMA. For the next 5 h, disruption of DPBs was correlated with an increase in permeability. A low concentration of HzOz (10-5 M) had no effect on either DPBs or permeability, whereas 104 M HzOz disrupted DPBs and increased permeability.Nitric oxide (NO) was involved in the redistribution ofF-actin and the alteration of permeability induced by Hz02 and PMA. Addition of L-arginine, a substrate of NO, increased the number of DPBs and maintained low permeability for up to 6 h in PMAtreated cells. The increase in permeability and disruption of DPBs induced by 10-4 M H202 could be prevented by L-arginine. On the other hand, nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO, disrupted DPBs and caused a direct increase in permeability in PMA-treated cells and in cells treated with both concentrations of Hz02.The involvement of NO in the regulation of endothelial transport by HzOz was cGMP-dependent. An analogue of cGMP, 8-Br-cGMP, prevented the disruption of DPBs and the increase in permeability induced by HzOz even when the production of NO was inhibited by L-NAME.The present findings indicate that the endothelial transport of solutes is associated with the cytoskeleton and that it can be regulated by H20 2 and PMA. The endogenous production of NO appears to be involved in this process via a cGMP-dependent pathway.