Sodium-dependent glucose transport by cultured proximal tubule cells.
The cotransport of sodium ion and alpha-methyl glucose, a non-metabolized hexose, was studied in rabbit proximal tubule cells cultured in defined medium. The rate of uptake of alpha-methyl glucose shows saturation kinetics, in which Km, but not Vmax, is dependent upon the Na+ concentration in the medium. The transport system was found to be of the high-affinity type, characteristic of the straight portion of the proximal tubule. Analysis of the rates of initial uptake within the context of a generalized cotransport model, suggests that two Na+ ions are bound in the activation of the hexose transport. The steady-state level of accumulation of alpha-methyl glucose also depends upon sodium concentration, consistent with the initial rate findings. The uptake of alpha-methyl glucose is inhibited by other sugars with the relative potencies of D-glucose greater than alpha-methyl glucose greater than D-galactose = 3-O methylglucose. L-Glucose, D-fructose, and D-mannose show no inhibition. Phlorizin inhibits the alpha-methyl glucose uptake with a Ki of 9 X 10(-6) M. Ouabain (10(-3) M) decreases the steady-state alpha-methyl glucose accumulation by 60%. In the absence of sodium, the accumulation of alpha-methyl glucose is 7-fold less than at 142 mM Na+, reaching a level comparable to the sodium-independent accumulation of 3-O-methyl-D-glucose. These findings are similar to those observed in the proximal tubule of the intact kidney.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D008954:Models, Biological; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology*
D008757:Methylglucosides; D008759:Methylglycosides; C027020:methylglucoside; D012964:Sodium