myo-Inositol transport in renal brush border vesicles and it inhibition by D-glucose.
We examined the mechanism of myo-inositol uptake by rabbit renal proximal tubule brush border membrane vesicles and characterized the relationship between the transports of myo-inositol and D-glucose. A 100 mM Na+ electrochemical gradient (extravesicular medium > intravesicular medium) stimulated the initial rate of myo-inositol uptake 20- to 60-fold. Other cation gradients were ineffective. The Na+ myo-inositol co-transport system was shown to be electrogenic. The Na+ electrochemical gradient-dependent uptake of myo-inositol saturated at about 1 mM myo-inositol, with an apparent Km of 94 micro M at an initial 100 mM Na+ gradient. D-Glucose was an inhibitor of the Na+ gradient-dependent uptake of myo-inositol. D-Glucose, but not L-glucose, elicited accelerative exchange diffusion of myo-inositol. myo-Inositol did not significantly inhibit the Na+ gradient-dependent transport of D-glucose. We suggest that D-glucose inhibits myo-inositol uptake by dissipating the membrane potential and sharing the myo-inositol carrier. The inhibition of myo-inositol transport across the brush border membrane by D-glucose explains how glycosuria could produce inosituria in patients with diabetes mellitus.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D066298:In Vitro Techniques; D007294:Inositol / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008353:Mannitol / Q000494:pharmacology; D008871:Microvilli / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
D008353:Mannitol; D007294:Inositol; D012964:Sodium; D005947:Glucose; D011188:Potassium