myo-inositol transport in rat intestinal brush border membrane vesicles, and its inhibition by D-glucose.

The uptake of myo-inositol into rat intestinal brush border membrane vesicles (BBMV) has been investigated. It is demonstrated that myo-inositol is transported into the vesicles by a secondary active process, specifically using the sodium gradient as the driving force. In the absence of sodium gradient, the transport reaction is still sodium dependent, and rheogenic, indicating that a myo-inositol/sodium cotransport is likely to occur. A kinetic analysis shows an hyperbolic saturation process with a Km of 0.16 +/- 0.02 mM with respect to myo-inositol and Vmax of 68.5 +/- 21.2 pmol/min per mg protein. The transport is inhibited by D-glucose, phloridzin and few other sugars. The mechanism of D-glucose inhibition appears to be of the mixed type. Finally, the myo-inositol transport is trans-activated by myo-inositol itself, but not by D-glucose. It is concluded that myo-inositol is transported into rat intestine BBMV by a specific transport system, which is also able to bind D-glucose, but not efficiently transport it across the membrane.