Transport ofl-cystine by rat renal brush border membrane vesicles

Abstract

Brush border membranes were isolated from rat renal cortex by a divalent cation precipitation method.l-³⁵S-cystine uptake into the vesicles was measured by a rapid filtration method. Covalent incorporation of tracer into membrane proteins was observed after prolonged incubations. At short incubation periods (1 min) binding was small and allowed an analysis of transmembrane transport. To guarantee transport ofl-cystine, the experiments were performed in the presence of the oxidant diamide. Sodium stimulatedl-cystine uptake specifically. A potassium/valinomycin induced inside negative diffusion potential stimulated sodium dependentl-cystine transport. Thus, transport is potential sensitive in the presence of sodium. At low substrate and inhibitor concentrations,l-cystine transport was inhibited byl-lysine,l-ornithine andl-arginine but not byd-lysine in the presence and absence of sodium. At higher inhibitor concentration, the neutral amino acidsl-phenylalanine andl-leucine also inhibitedl-cystine uptake, but only the sodium dependent uptake. These inhibition experiments suggest thatl-cystine is transported by the brush border membrane by a transport system for basic amino acids not necessarily requiring sodium. In addition, transport ofl-cystine can also procee via sodium dependent transport pathways for neutral amino acids. In the concentration range tested (up to 0.225 mmoles/l), no saturation ofl-cystine transport was observed in the presence and absence of sodium.