Biomaterial Database

Mechanism of transport of riboflavin in rabbit intestinal brush border membrane vesicles. 1993

H M Said, and R Mohammadkhani, and E McCloud

Medical Research Service, Veterans Affairs Medical Center-Long Beach, CA 90822.

Uptake of luminal riboflavin (RF) into the absorptive cells of rabbit small intestine was examined using purified brush border membrane vesicle (BBMV) preparations. These preparations were used in order to eliminate the interference of intracellular metabolism that occurs to the RF molecule during absorption. Uptake of RF by BBMV was found to be mainly (> 76%) the result of transport of the vitamin into the intracellular space with less binding to membrane surfaces. All 3H radioactivity that appeared in the intravesicular space after incubation with [3H]RF was found to be in the form of intact RF. Uptake of RF with time was independent of the presence or absence of a Na+ or a K+ gradient (out > in) and occurred without transaccumulation of the substrate in the intravesicular space. Furthermore, changing the incubation buffer pH showed minimal effect on RF uptake. When examined as a function of concentration, the initial rate of RF uptake was found to be saturable both in jejunal and ileal BBMV with an apparent Km of 7.24 +/- 1.06 and 8.88 +/- 0.90 microM and Vmax of 24.31 +/- 1.48 and 34.24 +/- 1.55 pmol/mg protein/5 sec, respectively. Unlabeled RF and the related compounds lumiflavin, 8-aminoriboflavin, isoriboflavin, and lumichrome all inhibited (but to different degrees) the uptake of physiologic concentration of [3H]RF. On the other hand, 8-hydroxyriboflavin, lumazine, and D-ribose all failed to inhibit [3H]RF uptake. Similarly, the membrane transport inhibitors DIDS, SITS, and furosemide all failed to inhibit [3H]RF uptake. The uptake of RF was found to be insensitive to changes in the transmembrane electrical potential, as shown by studies with anion substitution and valinomycin K(+)-induced negative or positive intravesicular potential methodologies. These results indicate that RF uptake by rabbit intestinal BBMV occurs via a carrier-mediated system that is Na+ independent in nature and transports the substrate by an electroneutral process. The role of this system in the overall absorption process of RF is discussed.

UI	MeSH Term	Description	Entries
D007082	Ileum	The distal and narrowest portion of the SMALL INTESTINE, between the JEJUNUM and the ILEOCECAL VALVE of the LARGE INTESTINE.
D007413	Intestinal Mucosa	Lining of the INTESTINES, consisting of an inner EPITHELIUM, a middle LAMINA PROPRIA, and an outer MUSCULARIS MUCOSAE. In the SMALL INTESTINE, the mucosa is characterized by a series of folds and abundance of absorptive cells (ENTEROCYTES) with MICROVILLI.	Intestinal Epithelium,Intestinal Glands,Epithelium, Intestinal,Gland, Intestinal,Glands, Intestinal,Intestinal Gland,Mucosa, Intestinal
D007583	Jejunum	The middle portion of the SMALL INTESTINE, between DUODENUM and ILEUM. It represents about 2/5 of the remaining portion of the small intestine below duodenum.	Jejunums
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D008727	Methotrexate	An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of TETRAHYDROFOLATE DEHYDROGENASE and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA.	Amethopterin,Methotrexate Hydrate,Methotrexate Sodium,Methotrexate, (D)-Isomer,Methotrexate, (DL)-Isomer,Methotrexate, Dicesium Salt,Methotrexate, Disodium Salt,Methotrexate, Sodium Salt,Mexate,Dicesium Salt Methotrexate,Hydrate, Methotrexate,Sodium, Methotrexate
D008871	Microvilli	Minute projections of cell membranes which greatly increase the surface area of the cell.	Brush Border,Striated Border,Border, Brush,Border, Striated,Borders, Brush,Borders, Striated,Brush Borders,Microvillus,Striated Borders
D009928	Organ Specificity	Characteristic restricted to a particular organ of the body, such as a cell type, metabolic response or expression of a particular protein or antigen.	Tissue Specificity,Organ Specificities,Specificities, Organ,Specificities, Tissue,Specificity, Organ,Specificity, Tissue,Tissue Specificities
D009994	Osmolar Concentration	The concentration of osmotically active particles in solution expressed in terms of osmoles of solute per liter of solution. Osmolality is expressed in terms of osmoles of solute per kilogram of solvent.	Ionic Strength,Osmolality,Osmolarity,Concentration, Osmolar,Concentrations, Osmolar,Ionic Strengths,Osmolalities,Osmolar Concentrations,Osmolarities,Strength, Ionic,Strengths, Ionic
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.