RT Journal Article SR Electronic T1 Riboflavin Uptake in Human Trophoblast-Derived BeWo Cell Monolayers: Cellular Translocation and Regulatory Mechanisms JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 264 OP 271 VO 298 IS 1 A1 Huang, Se-Ne A1 Swaan, Peter W. YR 2001 UL http://jpet.aspetjournals.org/content/298/1/264.abstract AB Riboflavin (vitamin B2) is essential for fetal development and must be acquired from maternal sources. The uptake mechanism of riboflavin and the major regulatory pathways involved were characterized in a model for the placental barrier, the human choriocarcinoma cell line, BeWo. Uptake of [3H]riboflavin was saturable (Kt = 1.32 ± 0.68 nM, Jmax = 266.63 ± 26.89 fmol/mg of protein/20 min), and was significantly reduced at low temperature and in the presence of metabolic inhibitors (azide, 2-deoxyglucose) or structural analogs. Ouabain, amiloride, sodium-free buffers, and medium with pH values ranging from 3 to 8 did not affect uptake of [3H]riboflavin. In contrast, substitution of chloride with other monovalent anions significantly inhibited its uptake. Induced differentiation of BeWo cells into syncytiotrophoblasts by forskolin or 8-bromo-cyclic adenosine monophosphate introduced a time-dependent decrease of riboflavin uptake. Preincubation with activators of cyclic nucleotide-dependent protein kinase pathways (3-isobutyl-1-methylxanthine andp-chlorophenylthio-cyclic guanosine monophosphate) and calmodulin antagonists (calmidazolium and W-13) resulted in a concentration-dependent reduction of [3H]riboflavin uptake, whereas specific modulators of protein kinase C pathways did not have significant effects. 3-Isobutyl-1-methylxanthine exerted its regulatory effect on riboflavin uptake via decreasing bothKt and Jmax of the riboflavin uptake process (Kt = 6.32 ± 1.29 nM, Jmax = 135.57 ± 10.42 fmol/mg of protein/20 min). In summary, we report the presence of high- affinity riboflavin transporter(s) on the microvillous membrane of BeWo cells that appears to be modulated by cellular cyclic nucleotide levels and calmodulin. The American Society for Pharmacology and Experimental Therapeutics