title: The effects of the extracellular manganese concentration and variation of the interpulse delay time in the CPMG sequence on water exchange time across erythrocyte membranes.
abstract: There has been broad disagreement in the literature regarding the dependence of water exchange times (Te) across erythrocyte membranes studied by the 1H-NMR Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence on extracellular Mn2+ concentration. While some workers saw no change in Te with Mn2+, others reported a 35-50% decrease in Te with this extracellular paramagnetic relaxation agent. We present 1H-NMR evidence that a 30-50% change in Te can be produced by interdependence of the interpulse delay time of the CPMG pulse sequence and the external Mn2+ concentration. Such a large dependency is interpreted in terms of the diffusional effect as a major source. However, it is shown experimentally that if a large number of refocusing pi pulses are used, the observed transverse relaxation times are unaffected by Mn2+. Under these conditions excellent agreement of Te obtained in our study (13.0 +/- 0.64 ms (N = 36) at 21 degrees C) and that of 12.8 +/- 3.6 ms at 20-23 degrees C reported by the radiotracer method was found. Our findings suggest new and important implications for evaluating the previous reports of the 1H-NMR CPMG method concerning the [Mn2+] effect in the decrease of Te, and provide conditions where studies of water transport across erythrocyte membranes using this magnetic resonance method can be used with confidence.
authors.affiliation: Department of Chemistry, University of Kentucky, Lexington 40506-0055.
authors.forename: L N
authors.initials: LN
authors.lastname: Chao
authors.forename: D A
authors.initials: DA
authors.lastname: Butterfield
mesh_terms: D001692:Biological Transport; D001834:Body Water / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D008345:Manganese