Transport of folic acid (Pte-Glu) across the brush-border membrane of human intestine was studied using brush-border membrane vesicle (BBMV) technique. The transport of Pte-Glu was higher in BBMV prepared from the jejunum than those prepared from the ileum (0.70 ± 0.05 and 0.14 ± 0.02 pmol·mg protein-1·10 s-1, respectively). The transport of Pte-Glu appeared to be carrier mediated and was 1) pH dependent and increased with decreasing incubation buffer pH; 2) saturable (K(t) = 1.69 μM, V(max) = 4.72 pmol·mg protein-1·10 s-1); 3) inhibited in a competitive manner by the structural analogues 5-methyltetrahydrofolate, methotrexate, and 5-formyltetrahydrofolate (K(i) = 2.2, 1.4 and 1.4 μM, respectively); 4) not affected by inducing a relatively positive or negative intravesicular compartment; 5) independent of Na+ gradient; and 6) inhibited by 4,4'-diisothiocyanatostilibene-2,2'-disulfonic acid (DIDS), an anion exchange inhibitor. The increase in Pte-Glu transport on decreasing incubation buffer pH appeared to be in part mediated through a direct effect of acidic pH on the transport carrier and in part through the pH gradient imposed by activating Pte-Glu-:OH- exchange and/or Pte-Glu-:H+ cotransport mechanisms. The important role of an acidic extravesicular environment in Pte-Glu transport is consistent with a role for the intestinal surface acid microclimate in folate transport. These results demonstrate that Pte-Glu transport in human BBMV occurs by a carrier-mediated system that is similar to that described for rat and rabbit intestinal BBMV.
|Original language||English (US)|
|Journal||American Journal of Physiology - Gastrointestinal and Liver Physiology|
|Issue number||2 (15/2)|
|State||Published - 1987|
ASJC Scopus subject areas
- Physiology (medical)