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>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 μM to 10 mM demonstrated a single saturable transport system with apparent K m = 996 μM and V max = 348 pmol glycine/mg protein per min. Inhibition observed when the Na +-dependent uptake of 25 μM 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.