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Free keywords:
Glucose; 2-Deoxy-d-glucose; Intracellular compartmentalization; Proximal tubule; Contraluminal membrane
Abstract:
In order to study contraluminal hexose transport, concentration and time-dependent influx of 3H-2-deoxy-D-glucose from the interstitium into cortical tubular cells has been measured. The influx curves fit to a two parameter kinetics (Km 1.3±0.2 mmol/L, Jmax 0.67±0.16 pmol/s · cm) plus an additional diffusion term (with P=6·10−8 cm2/s) and a distribution ratio extracellular to intracellular amount of 2-deoxy-D-glucose of 1∶0.6. Since the extracellular to intracellular free water space as estimated from morphological data was 1∶2, one must conclude that glucose has only free access to 1/3 of the cell water. The intracellularly accessible space was augmented when the tubules were preperfused for 10 s with hypotonic saline. Thereby an increase of the compartment into which diffusion occurs was revealed and a final rupture of this intracellular compartment at 1/4 isotonic solutions was observed. Total replacement of ions in the peritubular perfusate by mannitol did not change 2-deoxy-D-glucose influx, indicating that it is Na+-independent. By adding isotonic concentrations of the respective sugars to the capillary perfusate, three degrees of inhibition of 2-deoxy-D-glucose influx could be revealed: strong inhibition byd-glucose, methyl-β-D-glucoside, D-mannose, 3-O-methyl-D-glucose, 2-deoxy-D-galactose, methyl-β-D-galactoside and 6-deoxy-D-glucose, moderate inhibition by D-galactose, L-glucose, -mannose and galactose, 5-thio-α-D-glucose, myo-inositol and mannitol. The contraluminal 2-deoxy-D-glucose influx was also inhibited by phloretin, chlormerodrin and preperfusion with cytochalasin B. Starvation as well as streptozotocin diabetes has no influence on contraluminal 2-deoxy-D-glucose transport. Thus, in contrast to the luminal hexose transport system the contraluminal system is Na+-independent, does not require on OH-group at C-atom 2, accepts L-glucose and fructose, but not an α-methyl group at C-atom 1.
