Barrier function of epithelia

Abstract

The ability of an epithelium to prevent permeation of noxious agents has not been well studied except in the gastrointestinal tract where exclusion of H+ has clinical significance. This article reviews the permeation routes across epithelia both as elucidated in the extensive electrophysiological work done in recent years and as demonstrated in morphological studies. We thus place concepts about gastrointestinal barrier function into the framework of transport physiology. Both the permeability and permselectivity of epithelial barriers are reviewed here. The effects of physical agents (pressure and electric current), polyvalent cations, organic compounds with both specific (channel blocking) and nonspecific (detergent) membrane properties, cyclic nucleotides, microfilament-active agents, and particularly H+ on both the barrier function (permeability and permselectivity) and transport function of epithelia are considered. Based on the available data, an important role for active Na+ transport in the maintenance of the epithelial barrier function can be postulated.

Tight junction-based epithelial microenvironment and cell proliferation

“…Detailed epithelial electrophysiological analyses suggested the existence of paracellular aqueous pores or channels within TJs (Diamond, 1977;Claude, 1978;Powell, 1981;Reuss, 1992;Gumbiner, 1993). Based on the epithelial physiology, paracellular permeability/ transport constitutes a substantial part of the total permeability/transport through epithelial and endothelial cell sheets, the ratios of which vary relative to transcellular transport, depending on different cell types .…”

Neutrophil migration across cultured intestinal epithelial monolayers is modulated by epithelial exposure to IFN-gamma in a highly polarized fashion.

“…For example, the transepithelial resistance of even "leaky" epithelia is on the order of 100 ohm.cm 2, while many epithelia have resistances of several hundred to several thousand ohm.cm 2 (Powell, 1981). In contrast, cable analysis studies of the mesenteric microvasculature suggests that even physiologically confluent endothelium (except for that of the brain which has resistance >1,000 ohm.cm 2) has an average resistance of only a few ohm.cm 2 (on average, <2 ohm.cm2; Crone and Christensen, 1981).…”

DLG-1 Is a MAGUK Similar to SAP97 and Is Required for Adherens Junction Formation

“…One of these adhesion mechanisms is the formation of the tight junction or zonula occludens, which functions to regulate the permeability of the cell layer and to polarize the cell surface into apical and basolateral compartments (Mitic and Anderson, 1998). Tight junctions (in vertebrates) and septate junctions (in invertebrates) maintain the separation between the apical and basolateral surfaces by hindering the diffusion of lipids and proteins (Powell, 1981;Gumbiner, 1987). In contrast to tight junctions, a second mechanism of cell adhesion is the adherens junction, which is responsible for maintaining adhesion between neighboring cells and is important for intercellular communication (Muller, 2000;Vasioukhin and Fuchs, 2001).…”