Effect of phloretin on Na+-dependent D-glucose uptake by intestinal brush border membrane vesicles.
In the present work we studied the effects of phloretin on Na+-dependent D-glucose uptake by brush border membrane vesicles isolated from rabbit small intestine. Phloretin had no inhibitory effect on Na+-dependent D-glucose uptake in the presence of equilibrated Na+, although it inhibited the process in the presence of a Na+ gradient. Phlorizin inhibited Na+-dependent D-glucose uptake both in the presence and in the absence of a Na+ gradient. Phloretin and phlorizin competed with each other for the inhibition of Na+-energized D-glucose uptake. These results indicate that phloretin has no direct interaction with the Na+-dependent D-glucose transporter per se, though phloretin and phlorizin may have a common step(s) in their inhibition mechanisms. Phloretin, but not phlorizin, was found to increase the equilibrium level of D-glucose uptake whether Na+ was present or not. The increase in the equilibrium level was due to phloretin-induced binding of D-glucose to the brush border membrane, but not due to an increase in the intravesicular space. It seems to occur by a mechanism different from that by which phloretin inhibits Na+-energized D-glucose uptake, because the equilibrium level of D-glucose uptake is increased by the ionized form of phloretin but Na+-energized D-glucose uptake is inhibited by the unionized form.
D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D005947:Glucose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000648:ultrastructure*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D010693:Phloretin / Q000494:pharmacology*; D010695:Phlorhizin / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology*
D012964:Sodium; D010695:Phlorhizin; D005947:Glucose; D010693:Phloretin