Differences in neutral amino acid and glucose transport between brush border and basolateral plasma membrane of intestinal epithelial cells.
A comparison of L-valine and D-glucose transport was carried out with vesicles of plasma membrane isolated either from the luminal (brush border) or from the contra-luminal (basolateral) region of small intestinal epithelial cells. The existence of transport systems for both non-electrolytes was demonstrated by stereospecificity and saturability of uptake, as well as tracer coupling. Transport of L-valine and D-glucose differs markedly in the two types of plasma membrane with respect to stimulation by Na+. The presence of Na+ stimulated initial L-valine and D-glucose uptake in brush border, but not in basolateral membrane. Moreover, an electro-chemical Na+ gradient, oriented with the lower potential on the inside, supported accumulation of the non-electrolytes above medium concentration only in the brush border membrane. L-Valine and D-glucose transport also were saturated at lower concentrations in brush border (10-20 mM) than in basolateral plasma membranes (30-50 mM). A third difference between the two membranes was found in the effectiveness of known inhibitors of D-glucose transport. In brush border membranes phlorizin was more potent than phloretin and 2', 3', 4'-trihydroxy-4-methoxy chalcone and cytochalasin B did not inhibit at all. In contrast, with the basolateral plasma membranes the order of potency was changed to phloretin = 2',3',4'-trihydroxy-4-methoxy chalcone greater than cytochalasin B greater than phlorizin. These results indicate the presence of different types of transport systems for monosaccharides and neutral amino acids in the luminal and contra-luminal region of the plasma membrane. Active transepithelial transport can be explained on the basis of the different properties of the non-electrolyte transport systems in the two cellular regions and an electro-chemical Na+ gradient that is dependent on cellular metabolism.
D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D003571:Cytochalasin B / Q000494:pharmacology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006131:Growth Inhibitors / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism*; D007421:Intestine, Small; D009994:Osmolar Concentration; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013237:Stereoisomerism; D014633:Valine / Q000378:metabolism*
D006131:Growth Inhibitors; D003571:Cytochalasin B; D012964:Sodium; D010695:Phlorhizin; D014633:Valine; D005947:Glucose; D010693:Phloretin