D-galactose transport in rat intestinal brush border membrane vesicles studied with a molecular-sieve technique.

A technique using G-50 Sephadex molecular-sieve chromatography has been developed to study both the accumulation of transported solutes by rat intestinal brush border membrane vesicles and the wash-out of these solutes from pre-loaded vesicles. The extent to which D-galactose was taken up into the brush border membrane vesicles was dependent on the medium osmolarity and this dependence was significantly reduced (P less than 0.01) by pre-treating the vesicles with the non-ionic detergent Triton X-100. The transport of D-galactose into the brush border membrane vesicles was sodium dependent, electrogenic and phloridzin sensitive. It is, therefore, qualitatively similar to D-glucose transport into brush border membrane vesicles. The wash-out of D-galactose from pre-loaded brush border membrane vesicles was inhibited by phloridzin and accelerated by the presence of an outwardly directed sodium gradient. D-Galactose was released from the pre-loaded brush border membrane vesicles more slowly than D-glucose and this difference was consistent with the higher overshoot found for D-galactose during the transport of the sugars into the vesicles.