Stimulation of the efflux of L-glutamate from renal brush-border membrane vesicles by extravesicular potassium

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Abstract
The rate of efflux of L-glutamate from [rabbit] renal brush-border membrane vesicles was enhanced by Na+ and by extravesicular L-glutamate, but not by D-glutamate nor analogs of L-glutamate that do not share the Na+-L-glutamate co-transport system. Efflux seemed to be mediated by the Na+-L-glutamate carrier. The efflux of L-glutamate was increased by extravesicular K+ or Rb+ but not by Li+, choline+ or Tris+ [Tris (hydroxymethyl) aminomethane]. These findings, together with previous results showing that intravesicular K+ or Rb+ increased L-glutamate uptake and that a K+ gradient energized the concentrative uptake of the acidic amino acid in the absence of other gradients, provide evidence consistent with the hypothesis that the co-transport of Na+-L-glutamate is coupled to the transmembrane flux of K+.