title: Comparative transport efficiencies of urea analogues through urea transporter UT-B.
abstract: Expression of urea transporter UT-B confers high urea permeability to mammalian erythrocytes. Erythrocyte membranes also permeate various urea analogues, suggesting common transport pathways for urea and structurally similar solutes. In this study, we examined UT-B-facilitated passage of urea analogues and other neutral small solutes by comparing transport properties of wildtype to UT-B-deficient mouse erythrocytes. Stopped-flow light-scattering measurements indicated high UT-B permeability to urea and chemical analogues formamide, acetamide, methylurea, methylformamide, ammonium carbamate, and acrylamide, each with P(s)>5.0 x 10(-6) cm/s at 10 degrees C. UT-B genetic knockout and phloretin treatment of wildtype erythrocytes similarly reduced urea analogue permeabilities. Strong temperature dependencies of formamide, acetamide, acrylamide and butyramide transport across UT-B-null membranes (E(a)>10 kcal/mol) suggested efficient diffusion of these amides across lipid bilayers. Urea analogues dimethylurea, acryalmide, methylurea, thiourea and methylformamide inhibited UT-B-mediated urea transport by >60% in the absence of transmembrane analogue gradients, supporting a pore-blocking mechanism of UT-B inhibition. Differential transport efficiencies of urea and its analogues through UT-B provide insight into chemical interactions between neutral solutes and the UT-B pore.
authors.affiliation: Department of Medicine, 1246 Health Sciences East Tower, University of California, San Francisco, CA 94143-0521, USA.
authors.forename: Dan
authors.initials: D
authors.lastname: Zhao
authors.forename: N D
authors.initials: ND
authors.lastname: Sonawane
authors.forename: Marc H
authors.initials: MH
authors.lastname: Levin
authors.forename: Baoxue
authors.initials: B
authors.lastname: Yang
mesh_terms: D020106:Acrylamide / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability; D004058:Diffusion; D004912:Erythrocytes / Q000378:metabolism; D005559:Formamides / Q000494:pharmacology; D008051:Lipid Bilayers / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008782:Methylurea Compounds / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D013890:Thiourea / Q000494:pharmacology; D014508:Urea / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D005559:Formamides; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; D008782:Methylurea Compounds; C452857:urea transporter B, mouse; D020106:Acrylamide; C031066:formamide; D014508:Urea; D013890:Thiourea; C002950:methylformamide