title: 7Li NMR relaxation study of Li+ binding in human erythrocytes.
abstract: We used 7Li NMR spin-lattice (T1) and spin-spin (T2) relaxation time measurements to investigate the binding of Li+ in human red blood cell (RBC) suspensions. In RBCs containing 1.4 mM Li+, the intracellular 7Li NMR T2 relaxation value (0.30 +/- 0.03 s) was much smaller than the corresponding T1 value (6.0 +/- 0.1 s), yielding a ratio of T1 to T2 of 20. For 1.5 mM LiCl solutions whose viscosities were adjusted to 5 cP with glycerol, the values of the T1/T2 ratios were as follows: 49 for unsealed RBC membrane (2.0 mg of protein/mL); 4.4 for spectrin (1.9 mg/mL); 1.5 for 5.4 mM 2,3-bisphosphoglycerate (BPG); 2.2 for 2.7 mM carbonmonoxyhemoglobin (COHb); 1.6 for 2.0 mM ATP; and 1.2 for a 50/50% (v/v) glycerol-water mixture. Intracellular viscosity and the electric field gradients experienced by Li+ when traversing the spectrin-actin network therefore are not responsible for the large values of the T1/T2 ratios observed in Li(+)-loaded RBCs. We conclude that the RBC membrane is the major Li+ binding site in Li(+)-loaded RBCs (Kb = 215 +/- 36 M-1) and that the binding of Li+ to COHb, BPG, spectrin-actin, or ATP is weak. Partially relaxed 7Li NMR spectra of Li(+)-containing RBC membrane suspensions indicated the presence of two relaxation components, one broad and one narrow.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, Loyola University of Chicago, Illinois 60626.
authors.forename: Q
authors.initials: Q
authors.lastname: Rong
authors.forename: M
authors.initials: M
authors.lastname: Espanol
authors.forename: D
authors.initials: D
authors.lastname: Mota de Freitas
authors.forename: C F
authors.initials: CF
authors.lastname: Geraldes
mesh_terms: D019794:2,3-Diphosphoglycerate; D000255:Adenosine Triphosphate / Q000097:blood; D001665:Binding Sites; D004163:Diphosphoglyceric Acids / Q000097:blood; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D008094:Lithium / Q000097:blood*; D009682:Magnetic Resonance Spectroscopy; D013049:Spectrin / Q000378:metabolism; D014783:Viscosity
chemical_list: D004163:Diphosphoglyceric Acids; D013049:Spectrin; D019794:2,3-Diphosphoglycerate; D000255:Adenosine Triphosphate; D008094:Lithium