FRUCTOSE TRANSPORT BY RAT INTESTINAL BRUSH-BORDER MEMBRANE-VESICLES - EFFECT OF HIGH FRUCTOSE DIET FOLLOWED BY RETURN TO STANDARD DIET

1. D-Fructose uptake in isolated rat intestinal brush border membrane comprised a simple diffusional component and a saturable, carrier-mediated, component. The latter did not follow typical Michaelis-Menten kinetics and appeared as a low affinity, high capacity process (K(t) = 110 mM, J(max) = 160.5 nmol/min.mg protein). 2. Carrier-mediated D-fructose uptake was highly specific, Na independent and unaffected by phloridzin and metabolic inhibitors. 3. Fructose feeding for 3 days resulted in an activation of D-fructose uptake after a latent period superior to 3 days. The increase was of relatively short duration since it was not further observed 6 days after the return to the standard diet. 4. The activation in D-fructose uptake was due to a slight decrease in K(t) and a marked increase in J(max) (from 160.5 to 306 nmol/min.mg protein), suggesting a rise in the number of transporters.