REGULATION OF TIGHT-JUNCTION PERMEABILITY DURING NUTRIENT ABSORPTION ACROSS THE INTESTINAL EPITHELIUM

Tight junctions are located at the luminal aspect of adjacent epitheli al cells and form a barrier that limits the paracellular diffusion of hydrophilic solutes. In recent years, evidence has accumulated to indi cate that tight-junction permeability is regulated by the absorption o f various nutrients. In this review, we present the physiological basi s and importance of tight-junction regulation in intestinal epithelium . The molecular structure of tight junctions and their interactions wi th the cell cytoskeleton as well as the physical and chemical forces t hat influence tight junction permeability are described, Much of this review addresses the controversial Pappenheimer hypothesis, which stat es that a major portion of intestinal glucose absorption occurs throug h tight junctions and not by saturable transcellular active transport. The absorption of a significant portion of glucose through tight junc tions requires increased junctional permeability, a very high intralum enal glucose concentration, and a sufficient osmotic gradient to promo te volume flow.