Role of sodium ion in transport of folic acid in the small intestine
The effect of sodium on folate transport across the intestinal luminal membrane was analyzed using two techniques: the influx chamber and isoalted brush-border membrane vesicles. Preincubation of tissue in Na -free medium did not have a consistent effect on folic acid influx provided that Na was present in the test solution. Replacement of Na in the test solution by choline resulted in a significant reduction of folic acid influx. However, when intestinal sheets that had been equilibrated in Na -free solution were exposed to test solutions containing either Na , Li , K , Rb , Cs , Tris , or guanidinium as main cations, folic acid influx was not significantly decreased. Concentration-dependence studies showed that replacement of Na by Rb did not affect the saturable mechanism of folate transport. Rather, a decrease in nonsaturable folic acid uptake accounted for the slightly reduced influx observed in the presence of Rb . Experiments with brush-border membrane vesicles revealed that methotrexate uptake was significantly higher in the presence of external Na than in the presence of K , but was not different from uptake in the presence of K plus valinomycin. These data suggest that 1) the saturable component of folate transport is not Na dependent, and 2) nonsaturable transport of folic acid across the luminal membrane occurs in part through a conductive pathway that involves a negatively charged species of folate and a cation whose membrane permeability affects the rate of folate transport. The importance of Na in this process in vivo derives from the fact that Na is the most permeant cation available at the absorptive site in the small intestine.
- Research Organization:
- Univ. of Chicago, IL
- OSTI ID:
- 6411591
- Journal Information:
- Am. J. Physiol.; (United States), Vol. 251:2
- Country of Publication:
- United States
- Language:
- English
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FOLIC ACID
INTESTINAL ABSORPTION
SODIUM CHLORIDES
BIOCHEMISTRY
TRITIUM COMPOUNDS
CARBON 14 COMPOUNDS
CARBOXYLIC ACIDS
CELL MEMBRANES
CESIUM CHLORIDES
IONS
LITHIUM CHLORIDES
METHOTREXATE
POTASSIUM CHLORIDES
RATS
RUBIDIUM CHLORIDES
SMALL INTESTINE
ABSORPTION
ALKALI METAL COMPOUNDS
AMINO ACIDS
ANIMALS
ANTIMETABOLITES
AROMATICS
AZAARENES
BODY
CELL CONSTITUENTS
CESIUM COMPOUNDS
CHARGED PARTICLES
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
DIGESTIVE SYSTEM
DRUGS
GASTROINTESTINAL TRACT
HALIDES
HALOGEN COMPOUNDS
HEMATINICS
HEMATOLOGIC AGENTS
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
INTESTINES
LABELLED COMPOUNDS
LITHIUM COMPOUNDS
LITHIUM HALIDES
MAMMALS
MEMBRANES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
POTASSIUM COMPOUNDS
PTERIDINES
RODENTS
RUBIDIUM COMPOUNDS
SODIUM COMPOUNDS
UPTAKE
VERTEBRATES
VITAMIN B GROUP
VITAMINS
551001* - Physiological Systems- Tracer Techniques