Folate transport by human intestinal brush-border membrane vesicles

Area of Science:

• Gastroenterology
• Nutritional Science
• Cell Biology

Background:

• Folic acid (Pte-Glu) is essential for various metabolic processes.
• Understanding its intestinal absorption is crucial for nutritional and clinical applications.
• The brush-border membrane (BBM) is the primary site for nutrient absorption in the intestine.

Purpose of the Study:

• To investigate the mechanism of folic acid (Pte-Glu) transport across the human intestinal brush-border membrane.
• To characterize the kinetic and regulatory properties of this transport system.

Main Methods:

• Utilized the brush-border membrane vesicle (BBMV) technique with human intestinal samples.
• Assessed Pte-Glu uptake under varying pH conditions and in the presence of inhibitors.
• Analyzed kinetic parameters (Kt, Vmax) and inhibition by structural analogues.

Main Results:

• Pte-Glu transport was significantly higher in jejunal BBMV compared to ileal BBMV.
• Transport exhibited characteristics of a saturable, carrier-mediated system.
• The process was pH-dependent, increasing with lower incubation buffer pH.
• Competitive inhibition was observed with structural analogues like methotrexate.
• Transport was independent of Na+ gradient but sensitive to DIDS, an anion exchange inhibitor.

Conclusions:

• Human intestinal folic acid (Pte-Glu) transport across the BBMV is mediated by a carrier system.
• An acidic extravesicular environment, potentially the intestinal surface acid microclimate, plays a significant role.
• The identified transport mechanism is comparable to those observed in rat and rabbit intestinal BBMV.