title: Na+-H+ exchange in rat colonic brush-border membrane vesicles.
abstract: To demonstrate the presence of a Na+-H+ exchange process in brush-border membrane vesicles from rat colonocytes, the fluorescence response of acridine orange was used to monitor the formation and dissipation of pH gradients. An inwardly directed Na+ gradient stimulated the outward flux of H+, whereas proton influx was stimulated by an outwardly directed Na+ gradient. Since the ionophore valinomycin in the presence of a K+ gradient did not alter Na+-stimulated proton efflux, the interrelationship of Na+ and H+ movement could not be explained solely on the basis of a membrane potential. Na+-stimulated proton efflux was saturable with a Km for Na+ of 20.1 +/- 1.6 mM. Inwardly directed Li+ gradients also stimulated proton efflux, and the Km for Li+ was 30.2 +/- 1.7 mM. In contrast, impermeant cations failed to stimulate the outward flux of H+. Amiloride (1 mM) inhibited both Na+-stimulated proton efflux and influx. Therefore, Na+-H+ exchange is present in rat colonic brush-border membranes and has characteristics similar to other Na+-H+ antiporters. This exchange process may be an important mechanism for Na+ absorption in the large intestine.
mesh_terms: D000165:Acridine Orange; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D009550:Nigericin / Q000494:pharmacology; D011522:Protons; D051381:Rats; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D013050:Spectrometry, Fluorescence
chemical_list: D002352:Carrier Proteins; D005456:Fluorescent Dyes; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D008094:Lithium; D012964:Sodium; D000165:Acridine Orange; D009550:Nigericin