Dependence of the apparent thickness of the unstirred layer at the intestinal mucosa on nutrient concentration

The thickness of the intestinal unstirred layer determined with glycine is shown to increase from 247 ± 12 to 319 ± 14 μm (p < 0.001) as its concentration is raised from 5 to 40 mM; with glucose raised from 10 to 40 mM, the apparent value increases from 316 ± 13 to 380 ± 26 μm, because at higher concentrations the nutrients penetrate deeper to the bases of intestinal villi. The weak positive correlation between the apparent layer thickness (assayed with glucose, maltose, sucrose, alanine, leucine, and Gly-Ala in rats) and the parameter characterizing the rate of nutrient uptake (maximal short-circuit current response to nutrient) contradicts the assertion that the transporters are distributed uniformly along the villus height but because of high absorption in the upper part the nutrients do not reach the deeper transporters. It appears that the transporter distribution along the villi is nonuniform. The described method may serve to study the topography of nutrient transporters. © 2007 Pleiades Publishing, Inc.