title: Na(+)-H(+) exchange activity in brush-border membrane vesicles isolated from chick small intestine.
abstract: This study was undertaken to investigate the presence of a Na(+)-H(+) antiporter in brush-border membrane vesicles (BBMV) isolated from chick small intestine. An outwardly directed proton gradient (pH 5.5 inside, 7.5 outside) stimulated Na+ uptake into BBMV and resulted in a transient accumulation. No accumulation was observed in the absence of a proton gradient. Voltage clamping the membrane with K+ and valinomycin decreased the Na+ overshoot. Amiloride inhibited pH gradient-driven Na+ uptake in a dose-dependent manner with an IC50 of 44 microM. The relationship between pH gradient-driven Na+ uptake and external Na+ concentration followed simple, saturating Michaelis-Menten kinetics. Eadie-Hofstee analysis of the pH gradient-driven Na+ uptake indicated a single transport system with a Vmax of 33 nmol/mg protein per 15 s and a Km for Na+ of 12 mM. The initial rate of pH-driven Na+ uptake increased as the intravesicular pH decreased, with a Hill coefficient close to 1. These findings indicate that BBMV isolated from chicken small intestine possess a Na(+)-H(+) exchanger. This exchanger does not appear to be the one involved in cell pH regulation.
authors.affiliation: Departamento de Fisiología y Biología Animal, Facultad de Farmacia, Universidad de Sevilla, Spain.
authors.forename: M I
authors.initials: MI
authors.lastname: Ferrero
authors.forename: M
authors.initials: M
authors.lastname: Cano
authors.forename: A
authors.initials: A
authors.lastname: Ilundáin
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002645:Chickens; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D017923:Sodium-Hydrogen Exchangers; D014634:Valinomycin; D000584:Amiloride; D012964:Sodium; D011188:Potassium