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PubMed1992

The movement of solutes and cells across tight junctions.

The TJ is a highly dynamic rate-limiting barrier for passive transepithelial solute flow. It is not only physiologically regulated but is modulated in various disease states as well. Such modulations occur as a result of epithelial cell interactions with immune cells or immune cell products and thus epithelial barrier function appears to be regulated in disease states.

Abscess↗
PubMed1990

A factor in serum lowers resistance and opens tight junctions of MDCK cells.

During an inflammatory reaction, factors in blood affect the permeability of endothelium and possibly organ epithelium. In this study we partially characterized a factor in human and canine blood that lowered the transepithelial electrical resistance (TER) of canine kidney epithelial cells (MDCK) and examined whether vascular permeability factors [complement component C3a and C5a and platelet-activating factor (PAF)] were responsible for this reaction. C3a and C5a caused a small (10-13%) dose-related decrease in the TER (alpha = 0.05), whereas PAF had no effect. In contrast, the factor found in both serum and plasma caused a large (60-83%) dose-dependent decrease (saturated at 30%) in the TER that was reversible within 60 min. The blood factor, which does not appear to be albumin, was heat stable and has an apparent molecular mass of 67 kDa. It preferentially decreased the TER of the epithelium when it came in contact with its basolateral surface and significantly lowered the resistance within 60 min by opening the zonula occludentes. These findings suggest that C3a, C5a, and a factor in blood can directly modulate the permeability of renal epithelium.

Animals↗
PubMed1991

Function of rat hepatocyte tight junctions: studies with bile acid infusions.

To determine the effects of alteration of biliary paracellular permeability on bile flow and composition, we measured the biliary outputs of compounds highly concentrated in bile, all infused at a constant rate in the isolated rat liver perfused with Krebs-Henseleit buffer in a one-pass fashion. Paracellular permeability was increased by infusing 10(-8) M vasopressin (VP). The cholephilic compounds were three cations of various molecular weights, tributylmethylammonium (TBuMA), N-acetylprocainamide ethobromide (APAEB), and propidium iodide, and two anions, taurocholate (TC), a micelle-forming bile acid, and taurodehydrocholate (TDHC), an nonmicelle former. When TC was infused and paracellular permeability increased with VP, neither bile flow nor TC output changed, whereas outputs of cations fell. When TDHC was infused, TDHC output fell, as did outputs of all cations. The decrements in cation outputs exceeded that of TDHC and were inversely related to the molecular weight of the cation. To document that these changes were not related to reduced uptake of these compounds, we tested the uptakes of TBuMA, APAEB, and TDHC into isolated hepatocytes. In no case did 10(-8) M VP significantly reduce uptake. The data demonstrate that micelle-forming bile acids, with their high effective molecular weights, do not efflux from the biliary tree when permeability is increased with VP, whereas nonmicelle-forming bile acids do. Cations efflux more readily than anions, and within this group efflux rate is inversely related to molecular weight. The data confirm the size and charge selectivity of biliary tree permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Acecainide↗
PubMed1992

GLUT-1 glucose transporter is present within apical and basolateral membranes of brain epithelial interfaces and in microvascular endothelia with and without tight junctions.

We investigated the diversity of cellular localization of the GLUT-1 glucose transporter protein at epithelial and endothelial barriers either possessing or lacking occluding junctions. The avidin-biotin immunoperoxidase and the immunogold-silver staining (IGSS) techniques were used. A rabbit polyclonal antiserum prepared against a synthetic peptide encoding the 13 amino acids at the carboxyl terminus of the GLUT-1 glucose transporter protein was used. Both techniques were found to have comparable sensitivity in detecting immunoreactive GLUT-1. The IGSS experiments employed a light-insensitive stabilizer, and no immunoreactive GLUT-1 was found in brain cells (neurons, glial cells), but abundant immunoreactive GLUT-1 was found in brain capillary endothelium, which is composed of cells with occluding junctions. However, immunoreactive GLUT-1 was also found in endothelium known not to contain occluding junctions, such as testicular microvascular endothelium and endothelium on the fetal side of the syncytiotrophoblast of the placenta. In epithelial barriers, GLUT-1 was also found in the basolateral membrane of renal collecting duct epithelium, choroid plexus, and the placental syncytiotrophoblast layer. However, immunoreactive GLUT-1 was found in the apical membrane of ependymal epithelium near the lower portion of the third ventricle. In conclusion, there is diversity underlying the expression of the GLUT-1 glucose transporter protein in different cell types, and the transporter protein can be found in endothelium with and without occluding junctions, and in both apical and basolateral membranes of epithelial barriers.

Brain↗