title: Interactions between Na+-dependent uptake of D-glucose, phosphate and L-alanine in rat renal brush border membrane vesicles.
abstract: D-Glucose decreases phosphate reabsorption in rat proximal tubule. It is also postulated that some amino acids interact with phosphate reabsorption. To investigate the mechanism of these interactions, phosphate, D-glucose and L-alanine transport kinetics were measured in brush border membrane vesicles isolated from superficial rat kidney cortex by the calcium precipitation technique. At pH 7.4, Na+-dependent phosphate transport was inhibited in the presence of either D-glucose (39 mM) or L-alanine (2.4 mM). In this model, with D-glucose or with L-alanine the V value of the phosphate uptake was decreased, whereas the apparent Km for the phosphate uptake was not affected. However, some inhibition of phosphate transport was observed in the presence of L-glucose, D-alanine or D-glucose after phlorizin preincubation. A 30% Na+-dependent L-alanine (0.1 mM) transport inhibition was observed in the presence of 5 mM phosphate. D-Glucose (1 mM) was also inhibited by 20% when 5 mM phosphate was added to incubation medium. According to several authors, in our model, D-glucose decreased the L-alanine transport and vice versa. Moreover, when the membrane potential was abolished, a clear inhibition of D-glucose by L-alanine persisted. These multiple interactions could be explained by the accelerated dissipation of the Na+ gradient insofar as the rate of the Na+ uptake was increased with D-glucose, L-alanine or phosphate and since the absence of variations in membrane potentials did not suppress these inhibitions.
mesh_terms: D000409:Alanine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007672:Kidney Cortex / Q000648:ultrastructure*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology
chemical_list: D010710:Phosphates; D012964:Sodium; D005947:Glucose; D000409:Alanine