Overview of epithelial polarity

JS Handler - Annual review of physiology, 1989 - annualreviews.org
JS Handler
Annual review of physiology, 1989annualreviews.org
Polarity is the structural and functional hallmark of epithelia. The apical plasma membrane,
facing the organism's exterior (the lumen of the gut, renal tubule, glandular duct, or bile
canaliculus) differs in many important respects from the basolateral plasma membrane that
is apposed to adjacent epithelial cells (lateral plasma membrane), and to the basement
membrane (basal plasma membrane) and interior of the organism. Vectorial transport, a prin
cipal function of epithelia, depends on the polar distribution of plasma membrane …
Polarity is the structural and functional hallmark of epithelia. The apical plasma membrane, facing the organism's exterior (the lumen of the gut, renal tubule, glandular duct, or bile canaliculus) differs in many important respects from the basolateral plasma membrane that is apposed to adjacent epithelial cells (lateral plasma membrane), and to the basement membrane (basal plasma membrane) and interior of the organism. Vectorial transport, a prin cipal function of epithelia, depends on the polar distribution of plasma membrane constituents. To the extent that the same transporter is present in the apical and basolateral plasma membrane of an epithelial cell, substrate would be pumped into or out of the cell, rather than vectorially, across the epithelium. Figure 1 is an often reproduced schematic that depicts the com plex structure of intestinal epithelium. The apical plasma membrane, depicted with many microvilli, is the special organelle that gives the epithelium its specific functional characteristics. The basolateral plasma membrane, on the other hand, shares many characteristics with the plasma membranes of nonpo lar cells. It is usually the location of the (Na+ K)-ATPase, receptors for hormones and growth factors, transporters for ions and nutrients, and is the site of attachment to the basement membrane or other supporting material. Its special characteristics complement the special characteristics of the apical plasma membrane. For example, in epithelia that transport glucose from apical to basal surface, the apical membrane contains a sodium-coupled glucose transporter that moves glucose into the cell based on the driving force
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