title: Ethanol selectively affects Na+-gradient dependent intestinal transport systems.
abstract: Moderate concentrations of ethanol reduce the velocity of uptake of three representative Na+-symport systems (D-glucose, L-alanine, L-ascorbate), whether electrogenic (the first two) or electroneutral (L-ascorbate). This 'inhibition' is observed only if these transport systems are tested in the presence of an initial Na+ gradient (out greater than in); no inhibition is found in tracer-equilibrium exchange measurements. A representative Na+-independent system (D-fructose) is not inhibited by ethanol. 'Passive diffusion' (measured as uptake of L-glucose) is increased somewhat by alcohol. All these observations can be rationalized [as suggested by Tillotson et al. (1981) Arch. Biochem. Biophys. 207, 360-370] by an effect of ethanol on passive diffusion, which leads to a faster collapse of the Na+ gradient, with the resulting reduction of the uptake velocities of Na+-dependent transport systems when tested with the added driving force of an Na+ out----in gradient.
mesh_terms: D000409:Alanine / Q000378:metabolism; D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D004058:Diffusion; D000431:Ethanol / Q000494:pharmacology*; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D012964:Sodium / Q000502:physiology*
chemical_list: D005632:Fructose; D000431:Ethanol; D012964:Sodium; D005947:Glucose; D000409:Alanine; D001205:Ascorbic Acid