title: Inhibition of the proton-coupled folate transporter (PCFT-SLC46A1) by bicarbonate and other anions.
abstract: The proton-coupled folate transporter (PCFT) plays a key role in intestinal folate absorption, and loss-of-function mutations in the gene encoding this transporter are the molecular basis for hereditary folate malabsorption. Using a stable transfectant with high expression of PCFT, physiologic levels of bicarbonate produced potent and rapidly reversible inhibition of PCFT-mediated transport at neutral pH. Bisulfite and nitrite also inhibited PCFT function at neutral pH, whereas sulfate, nitrate, and phosphate had no impact at all. At weakly acidic pH (6.5), bisulfite and nitrite exhibited much stronger inhibition of PCFT-mediated transport, whereas sulfate and nitrate remained noninhibitory. Inhibition by bisulfite and nitrite at pH 6.5 was associated with a marked decrease in the influx Vmax and collapse of the transmembrane proton gradient attributed to the diffusion of the protonated forms into these cells. Monocarboxylates such as pyruvate and acetate also collapsed the pH gradient and were also inhibitory, whereas citrate and glycine neither altered the proton gradient nor inhibited PCFT-mediated transport. These observations add another dimension to the unfavorable pH environment for PCFT function in systemic tissues: the presence of high concentrations of bicarbonate.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Chanin 628, 1300 Morris Park Avenue, Bronx, NY 10461, USA. rongbao.zhao@einstein.yu.edu
authors.forename: Rongbao
authors.initials: R
authors.lastname: Zhao
authors.forename: Michele
authors.initials: M
authors.lastname: Visentin
authors.forename: Sylvia O
authors.initials: SO
authors.lastname: Suadicani
authors.forename: I David
authors.initials: ID
authors.lastname: Goldman
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology; D000838:Anions / Q000494:pharmacology; D001639:Bicarbonates / Q000494:pharmacology*; D045744:Cell Line, Tumor; D019343:Citric Acid / Q000494:pharmacology; D058972:Folic Acid Transporters / Q000378:metabolism; D005998:Glycine / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology; D058979:Proton-Coupled Folate Transporter / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011522:Protons; D019289:Pyruvic Acid / Q000494:pharmacology; D013447:Sulfites / Q000494:pharmacology
chemical_list: D000838:Anions; D001639:Bicarbonates; D058972:Folic Acid Transporters; D026901:Membrane Transport Proteins; D009566:Nitrates; D058979:Proton-Coupled Folate Transporter; D011522:Protons; C505058:SLC46A1 protein, human; D013447:Sulfites; D019343:Citric Acid; D019289:Pyruvic Acid; C042345:hydrogen sulfite; D019342:Acetic Acid; D005998:Glycine