title: Gradient coupling in isolated intestinal cells.
abstract: Work with isolated intestinal cells summarized below shows that: 1) An answer to the "energetic adequacy" question for Na+ -dependent transport systems cannot be provided unless solute fluxes by all routes are taken into account. 2) The conventional view of transport efficiency is in fact a measure of membrane leakiness to solute rather than a measure of innate efficiency for the Na+-dependent carrier. 3) Uncontrolled sugar-induced changes in membrane potential introduce a systematic error in measurements of the Na+: sugar coupling stoichiometry. 4) With appropriate control of the membrane potential the measured coupling ratio is 2 Na+ per sugar molecule. 5) A 2:1 coupling ratio allows for theoretical maximum sugar gradients of several hundred fold via a mechanism sharply dependent on the membrane potential.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D050260:Carbohydrate Metabolism; D004594:Electrophysiology; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials; D008954:Models, Biological; D012964:Sodium / Q000378:metabolism
chemical_list: D012964:Sodium