Transport of tricarboxylic acid cycle intermediates by membrane vesicles from renal brush border

Abstract

The uptake of citrate and alpha-ketoglutarate by membrane vesicles from rabbit renal brush border was studied by a rapid filtration technique. Both compounds exhibited transport characteristics similar to those seen for the sodium-dependent cotransport systems previously described for sugars and amino acids in brush border membranes. The estimated sodium-dependent Vmax and Km were 17 nmol per mg of protein per min and 0.18 mM for citrate and 17 nmol per mg of protein per min and 1.0 mM for alpha-ketoglutarate. The initial rate of citrate transport was 5 times that of sugars and amino acids under comparable conditions. Uptake rates of 0.1 mM citrate and alpha-ketoglutarate were inhibited by greater than 90% by 10 mM succinate, malate, fumarate, or oxaloacetate, indicating the presence in the brush border membrane of a transport system highly specialized for the renal conservation of intermediates of the tricarboxylic acid cycle.