EFFECT OF DIET ON GLUCOSE TRANSPORTER SITE DENSITY ALONG THE INTESTINAL CRYPT-VILLUS AXIS

High-carbohydrate diets stimulate intestinal brush-border glucose uptake and increase the number of glucose-protectable phlorizin binding sites, but it has been unknown where along the crypt-villus axis these effects are expressed. We attacked this problem by three methods. First, by measuring phlorizin binding to isolated mouse enterocytes fractionated along the crypt-villus axis by the Weiser method, we identified a high-affinity binding site predominating from villus tip to midvillus and a site of possibly lower affinity predominating in the crypts. A high-carbohydrate diet increased by severalfold the density of the villus sites and probably also of the crypt sites, without changing their binding constants. Second, autoradiography revealed increased glucose-protectable phlorizin binding along the whole crypt-villus axis on a high-carbohydrate diet. Finally, a polyclonal antibody against the Na+-glucose cotransporter recognized a protein in the brush-border membrane of villus cells. Hence, substrate-dependent upregulation of intestinal glucose transport involves increased numbers of transporters along the crypt-villus axis.