These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Functional roles of Na+ and H+ in SO2-4 transport by rabbit ileal brush border membrane vesicles.
    Author: Ahearn GA, Murer H.
    Journal: J Membr Biol; 1984; 78(3):177-86. PubMed ID: 6327990.
    Abstract:
    Sulphate uptake by rabbit ileal brush border membrane vesicles was stimulated by a transmembrane sodium gradient [( Na+]o greater than [Na+]i), but not by a similar potassium gradient. 35SO4(-2) influx ( JSO4 oi ) from outside (o) to inside (i) these vesicles was a hyperbolic function of [SO4-2]o and the affinity constant for anion transport was strongly influenced by [Na+]o (100 mM Na+, KSO4 t = 0.52 mM SO4 -2; 10 mM Na+, KSO4 t = 4.32 mM SO4-2). JSO4 oi was a sigmoidal function of [Na+]o at pH 7.4 for both low (0.2 M) and high (4.0 mM) [SO4-2]o. The Na+-dependency of JSO4 oi was examined at pH 6.0, 7.4, and 8.0 (same pH inside and outside). At pH 6.0 and 7.4 sigmoidal Na+-dependent JSO4 oi exhibited nonlinear Eadie-Hofstee plots indicative of a transport mechanism capable of binding a variable number of sodium ions over the [Na+]o range used. Hill plots of anion transport under these conditions displayed slopes near unity at low [Na+]o and slopes approximating 2.0 at higher cation concentrations. At pH 8.0, Na+-dependent JSO4 oi was hyperbolic and showed linear Eadie-Hofstee and Hill plots, the latter with a single slope near 1.0. When a H+ gradient was imposed across the vesicle wall (pHi = 8.0, pHo = 6.0), Na+-dependent JSO4 oi was hyperbolic and significantly increased at each [Na+]o over values observed using bilateral pH 8.0. In contrast, a H+ gradient oriented in the opposite direction (pHi = 6.0, pHo = 8.0) led to Na+-dependent JSO4 oi that was sigmoidal and significantly lower at each [Na+]o than values found using bilateral pH 6.0. Electrogenicity of JSO4 oi at pH 8.0 for both high and low [Na+]o was demonstrated by using a valinomycin-induced transmembrane electrical potential difference. At pH 6.0, electrogenic JSO4 oi occurred only at low [Na+]o (5 mM); anion transfer was electroneutral at 50 mM Na+. A model is proposed for proton regulation of sodium sulphate cotransport where flux stoichiometry is controlled by [H+]i and sodium binding affinity is modified by [H+]o. Preliminary experiments with rabbit proximal tubular brush border membrane vesicles disclosed similar JSO4 oi kinetic properties and a common transport mechanism may occur in both tissues.
    [Abstract] [Full Text] [Related] [New Search]