The in vivo localization of high-affinity phlorizin receptors to the brush border surface of the proximal tubule in dog kidney

Abstract

The interaction of [ 3H]phlorizin (spec. act. 5 Ci/mmole) with canine renal tubular surfaces has been investigated in vivo, using the multiple indicator dilution technique. 1. 1. Over short observation periods there is no observable interaction between tracer phlorizin and the antiluminal (peritubular) surface. Instead, phlorizin appears to have a limited volume of distribution relative to the extracellular reference (creatinine), from the postglomerular circulation. 2. 2. Phlorizin and creatinine are filtered to the same degree at the glomerulus however the urine recovery of [ 3H]phlorizin is 5–10% of the glomerular marker (plasma glucose concentration 60–124 mg/100 ml). 3. 3. The remaining 90–95% can be “washed off” and recovered in the urine within minutes after the systemic administration of a pulse of unlabelled phlorizin or glucose. Preloading of animals with phlorizin or glucose also increases the urine recovery of [ 3H]phlorizin relative to control conditions. In contrast the urine recovery of [ 3H]phlorizin is unaffected by phloretin infusion. 4. 4. It is concluded that only one set of high-affinity phlorizin receptors is present in dog kidney, and that these are located along the brush border of the proximal tubule, in close association with the glucose-transport mechanism.