Gut tissue from each region, such as ileum and colon, is opened along the mesenteric border and mounted in Ussing chambers (Physiologic Instruments), exposing 0.3 cm² of tissue to 2.5 mL of oxygenated Krebs-glucose (10 mM) on the serosal side and Krebs-mannitol (10 mM) on the luminal side, at 37°C. Paracellular and transcellular permeability are then measured. Charged per sample, with a minimum of 8 samples.