title: Involvement of a receptor-mediated component in cellular translocation of riboflavin.
abstract: This study addresses the transport mechanism of riboflavin (vitamin B(2)) across intestinal epithelium in the presence and absence of pharmacologically active compounds. A polarized transport process with a 6-fold higher basolateral (BL)-to-apical (AP) flux was observed in both a human intestinal cell model (Caco-2) and rat intestinal tissue. Riboflavin-specific translocation systems on both the AP and BL cell surfaces were saturable with affinity values close to most receptors (K(m): 9.72 +/- 0.85 and 4.06 +/- 0.03 nM, respectively). Pharmacological agents known to alter intracellular endocytic events were used to examine the potential involvement of receptor-mediated events. Nocodazole significantly inhibited AP uptake (58.4%), BL-to-AP riboflavin (56.7%) and fluorescein isothiocyanate-labeled transferrin (FITC-Tf) (31.8%) transport without affecting mannitol or cholic acid transport, whereas AP-to-BL riboflavin (252.8%) and FITC-Tf (145.1%) transport was increased. Brefeldin A significantly enhanced AP-to-BL riboflavin (37.1%) and bidirectional FITC-Tf transport (AP-to-BL: 13-fold; BL-to-AP: 5-fold). without affecting BL-to-AP riboflavin transport. Combined, these data suggest an essential role of microtubule-dependent movement and vesicular sorting component(s) in the bidirectional transport of riboflavin. Dissociation of riboflavin from the cell surface was pH-dependent with significantly higher substrate release at acidic pH, indicating the presence of riboflavin-specific cell surface receptors. In summary, our studies provide biochemical evidence of the involvement of a receptor-mediated mechanism in the cellular translocation of riboflavin.
authors.affiliation: Division of Pharmaceutics, College of Pharmacy, The Ohio State University, Columbus, Ohio 43210-1291, USA.
authors.forename: S N
authors.initials: SN
authors.lastname: Huang
authors.forename: P W
authors.initials: PW
authors.lastname: Swaan
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D011956:Receptors, Cell Surface / Q000502:physiology*; D012256:Riboflavin / Q000493:pharmacokinetics*; D013997:Time Factors
chemical_list: D011956:Receptors, Cell Surface; D012256:Riboflavin