title: Urea exchange across the human erythrocyte membrane measured using 13C NMR lineshape analysis.
abstract: The 13C NMR spectrum of 13C-urea in a suspension of human red cells of reduced mean cell volume was observed to contain partially resolved resonances arising from the intra- and extracellular populations of the compound. It was shown that at 25 degrees C and a magnetic field strength of 9.4 T, the rate of exchange of urea between the intra- and extracellular populations was such that the NMR lineshape was sensitive to a change in the rate of 13C-urea exchange, induced either by the addition of the urea transport inhibitor phloretin, or by the addition of 12C-urea. Total lineshape analysis of 13C NMR spectra of 13C-urea in red cell suspensions containing different concentrations of 12C-urea resulted in a weighted mean estimate for the Km and Vmax for urea equilibrium exchange from three experiments of 44 +/- 18 mM and 3.1 +/- 0.6 x 10(-8) mol cm-2 s-1, respectively (the errors denote the weighted mean standard deviations). These estimates of Km and Vmax were significantly lower than previous values reported in the literature and determined using other techniques.
authors.affiliation: Department of Biochemistry, University of Sydney, N.S.W., Australia.
authors.forename: J R
authors.initials: JR
authors.lastname: Potts
authors.forename: B T
authors.initials: BT
authors.lastname: Bulliman
authors.forename: P W
authors.initials: PW
authors.lastname: Kuchel
mesh_terms: D000328:Adult; D002247:Carbon Isotopes; D002463:Cell Membrane Permeability; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008432:Mathematical Computing; D013057:Spectrum Analysis / Q000379:methods; D014508:Urea / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D002247:Carbon Isotopes; D014508:Urea