Uptake of d-Glucose by Renal Tubule Membranes

Abstract d-[14C]Glucose was taken up by a cell-free, membrane-rich, particulate fraction prepared from isolated rabbit renal tubules by processes which showed temperature and phlorizin sensitivity, stereospecificity, sodium dependence, and saturability. The amount of d-glucose taken up and metabolized by the membrane preparation as well as the time course observed indicate that this uptake process represents transport into membrane-lined vesicles rather than binding to membrane fragments. Kinetic analyses in the presence and absence of sodium revealed that the uptake of d-glucose was mediated by two distinct systems: one with a high affinity and low capacity for glucose and a requirement for sodium ions; a second with low affinity and high capacity for glucose and no sodium requirement. Additional evidence for these two systems was obtained from experiments with other unlabeled sugars which showed qualitative and quantitative differences in inhibition of d-[14C]glucose uptake.