Na+-dependent transport of glycine in renal brush border membrane vesicles. Evidence for a single specific transport system

Abstract

The uptake of glycine in rabbit renal brush border membrane vesicles was shown to consist of glycine transport into an intravesicular space. An Na+ electrochemical gradient (extravesicular greater than intravesicular) stimulated the initial rate of glycine uptake and effected a transient accumulation of intravesicular glycine above the steady-state value. This stimulation could not be induced by the imposition of a K+, Li+ or choline+ gradient and was enhanced as extravesicular Na+ was increased from 10 mM to 100 mM. Dissipation of the Na+ gradient by the ionophore gramicidin D resulted in diminished Na+-stimulated glycine uptake. Na+-stimulated uptake of glycine was electrogenic. Substrate-velocity analysis of Na+-dependent glycine uptake over the range of amino acid concentrations from 25 microM to 10 mM demonstrated a single saturable transport system with apparent Km = 996 microM and Vmax = 348 pmol glycine/mg protein per min. Inhibition observed when the Na+-dependent uptake of 25 microM glycine was inhibited by 5 mM extravesicular test amino acid segregated dibasic amino acids, which did not inhibit glycine uptake, from all other amino acid groups. The amino acids D-alanine, D-glutamic acid, and D-proline inhibited similarly to their L counterparts. Accelerative exchange of extravesicular [3H]glycine was demonstrated when brush border vesicles were preloaded with glycine, but not when they were preloaded with L-alanine, L-glutamic acid, or with L-proline. It is concluded that a single transport system exists at the level of the rabbit renal brush border membrane that functions to reabsorb glycine independently from other groups of amino acids.