Sugar uptake into brush border vesicles from dog kidney. I. Specificity

Abstract

This study describes the specificity of uptake of sugars into osmotically active vesicles derived from a purified membrane fraction from dog kidney cortex. [ 3H]Phlorizin binding experiments have also been carried out in vesiculated and non-vesiculated membrane preparations. 1. 1. We demonstrate the existence of a sodium-dependent, phlorizin-sensitive d-glucose transport system in the vesiculated membrane preparation. 2. 2. This transport system has similar specificity characteristics to those observed in vivo for the glucose transporter in the brush border membrane of the proximal tubule. 3. 3. We also observe a sodium-dependent, glucose-sensitive phlorizin receptor in the same preparation with a K d for phlorizin ⋍0.3 μ M and K I for glucose ⋍3 mM at 37°C, pH 7.4, 100 mM NaCl. 4. 4. Detailed results relating to the specificity of inhibition of high affinity phlorizin binding are obtained using non-vesiculated brush border membrane fragments in the presence of d-glucose, α-methyl- d-glucoside, d-galactose, β-methyl- d-galactoside, 2-deoxy- d-glucose and d-mannose. 5. 5. Uptake studies using vesiculated membrane fragments from newborn dog kidney indicate that the brush border d-glucose transporter is already at an advanced stage of development at birth. Our results demonstrate that the d-glucose transport system from the dog proximal tubule brush border membrane together with its phlorizin receptor moiety is preserved intact in our membrane vesicle preparation.