Sugar transport in isolated rat kidney papillary collecting duct cells

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Abstract
D-Glucose is an important substrate of energy metabolism and osmolyte synthesis in the renal papillary collecting duct. In order to characterize the cellular entry ofd-glucose in this tubular segment, collecting duct cells were isolated from rat kidney papilla and the rate ofd-glucose uptake was measured indirectly by monitoring thed-glucose-dependent O2 uptake in the presence of the uncoupler CCCP.d-Glucose uptake was found to be sodium-independent and not sensitive to phlorizin even at a concentration of 10−3 M. Uptake was, however, completely inhibited by 10−5 M cytochalasin B and 10−4 M phloretin. The apparentK i for cytochalasin B was 1.5×10−6 M and for phloretin 2.0×10−5 M. Studies on the substrate specificity revealed that at 1 mMd-mannose is taken up and metabolized to the same extent asd-glucose. A 50-fold higher concentration of 2-deoxy-d-glucose and 2-amino-2-deoxy-d-glucose inhibitedd-glucose uptake completely whereas α-methyl-d-glucoside,d-allose, andd-galactose were without effect. Under conditions whered-glucose utilization was maximally stimulated an apparentK m of 1.2 mM and aV max of 1 mmold-glucose/g protein hour was found ford-glucose uptake. These results indicate that thed-glucose uptake into papillary collecting duct cells is probably mediated by a transport system similar to the one found in basal-lateral membranes of pelarized renal, intestinal, and liver cells as well as in nonpolarized fat cells and erythrocytes.