NUTRIENT ABSORPTION IN THE SMALL-INTESTINE

Photoaffinity labeling of bile acid receptors in the mucosa have ident ified a 93-kD apical membranous protein and a 14-kD cytosolic protein, whereas using an expression cloning strategy, a complementary DNA clo ne encoding a predicted 38-kD protein has been identified. A lipoprote in with surfactant-like properties has been shown to be associated wit h lipid export from the intestine. Lipid transport can be blocked by t he in vivo administration of Brefeldin A. A neutral and basic amino ac id transporter was identified in the brush border of intestinal cells that is important in taurine absorption. Dipeptidyl peptidase IV was s hown to be physiologically important. Tyrosine kinase was suggested to be important in Na+-H+ exchange at the apical surface and NaCl absorp tion basolaterally. There is an excess of lactase messenger RNA compar ed with activity during the maturation process. Fasting/refeeding expe riments activate the early response genes c-fos and c-jun.