myo-Inositol transport in renal brush border vesicles and it inhibition by D-glucose
Hammerman, M.R.; Sacktor, B.; Daughaday, W.H.
American Journal of Physiology 239(2): F113-F120
1980
ISSN/ISBN: 0002-9513 PMID: 6773422 Document Number: 164142
The mechanism of myo-inositol uptake was examined in rabbit renal proximal tubule brush border membrane vesicles and the relationship between the transports of myo-inositol and D-glucose was characterized. 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+ my-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 .mu.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. D-Glucose may inhibit 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.