Sulphate-ion/sodium-ion co-transport by brush-border membrane vesicles isolated from rat kidney cortex

摘要

Uptake of SO4²⁻ into brush-border membrane vesicles isolated from rat kindey cortex by a Ca²⁺-precipitation method was investigated by using a rapid-filtration technique. Uptake of SO4²⁻ by the vesicles was osmotically sensitive and represented transport into an intra-vesicular space. Transport of SO4²⁻ by brush-border membranes was stimulated in the presence of Na⁺, compared with the presence of K⁺ or other univalent cations. A typical `overshoot' phenomenon was observed in the presence of an NaCl gradient (100mm-Na⁺ outside/zero mm-Na⁺ inside). Radioactive-SO4²⁻ exchange was faster in the presence of Na⁺ than in the presence of K⁺. Addition of gramicidin-D, an ionophore for univalent cations, decreased the Na⁺-gradient-driven SO4²⁻ uptake. SO4²⁻ uptake was only saturable in the presence of Na⁺. Counter-transport of Na⁺-dependent SO4²⁻ transport was shown with MoO4²⁻ and S2O3²⁻, but not with PO4²⁻. Changing the electrical potential difference across the vesicle membrane by establishing different diffusion potentials (anion replacement; K⁺ gradient±valinomycin) was not able to alter Na⁺-dependent SO4²⁻ uptake. The experiments indicate the presence of an electroneutral Na⁺/SO4²⁻-co-transport system in brush-border membrane vesicles isolated from rat kidney cortex.