A carrier-mediated transport for folate in basolateral membrane vesicles of rat small intestine.

摘要: The mechanism of exit folate from the enterocyte, i.e. transport across basolateral membrane, is not known. In this study we examined, using membrane vesicles, folic acid rat intestine. Uptake by these vesicles represents substrate into intravesicular compartment and binding to surface. rate was linear for first 1 min incubation but decreased thereafter, reaching equilibrium after 5 incubation. was: (1) saturable as a function concentration with an apparent Km 0.6 +/- 0.17 microM Vmax. 1.01 0.11 pmol/30 s per mg protein; (2) inhibited in competitive manner structural analogues 5-methyltetrahydrofolate methotrexate (Ki = 2 1.4 microM, respectively); (4) electroneutral; (5) Na+-independent; (6) sensitive effect anion exchange inhibitor 4,4'-di-isothiocyanatostilbene-2,2'-disulphonic (DIDS). These data indicate existence carrier-mediated system intestinal demonstrate that process electroneutral, Na+-independent inhibition.