Sugar uptake into brush border vesicles from normal human kidney.

Abstract

Uptake studies of simple sugars were preformed on a membrane fraction containing osmotically active vesicles prepared from normal human kidney cortex. The uptake of D-glucose was Na-dependent and phlorizin-sensitive. The specificity of the D-glucose transport mechanism was shared by .alpha.-methyl-D-glucoside, D-galactose and 5-thio-D-glucose, while 2-deoxy-D-glucose, 3-O-methyl-D-glucose, D-mannose and D-fructose showed little, if any, affinity. Measurement of the Na-dependent component of the initial D-glucose uptake as a function of glucose concentration resulted in a curvilinear Scatchard plot, indicating the possibility of cooperative effects, or alternatively, the existence of 2 (or more) Na-dependent D-glucose transporters. In the case of 2 transporters, Km .simeq. 0.3 mM and Vmax .simeq. 2.5 nmol/min per mg of protein for the high-affinity transporter and Km .apprx. 6 mM and Vmax .apprx. 8 nmol/min per mg of protein for the low-affinity transporter. The Na-dependent D-glucose transport mechanism characterized was localized in the brush border of the proximal tubule.