title: Uptake of 5-methyltetrahydrofolic acid by the rat jejunum.
abstract: 1. Everted sacs of rat jejunum were used to study the transport of 5-methyltetrahydrofolic acid at various concentrations and at different pHs. 2. The transport of 5-methyltetrahydrofolic acid appeared to be linear with increasing incubation time at a 5-methyltetrahydrofolic acid concentration of 10(-5) M in the incubating medium. Tissue uptake was much higher than serosal uptake. 3. At 'zero' concentration gradient of 5-methyltetrahydrofolic acid, the transport from mucosal to serosal sides was negligible but tissue uptake was appreciable. 4. Reducing the incubation temperature from 37 to 27 degrees C gave a Q10 value of 1-8. 5. The characteristics of 5-methyltetrahydrofolic acid uptake suggested a non-saturable transport mechanism. 6. Studies were also carried out with isolated mucosal epithelial cells at different incubation times and at different pH values. 7. The over-all results suggest that 5-methyltetrahydrofolic acid transport is most likely a passive diffusion of its zwitterion and also a solvent drag with water flow. 8. The 5-methyltetrahydrofolic acid may be converted to its zwitterion in an acid microclimate at the surface of the intestinal absorbing cell.
mesh_terms: D000818:Animals; D001692:Biological Transport; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism*; D008297:Male; D051381:Rats; D012704:Serous Membrane / Q000378:metabolism; D013696:Temperature; D013763:Tetrahydrofolates / Q000378:metabolism*
chemical_list: D013763:Tetrahydrofolates