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Titolo:
Competition between Na+ and Li+ for unsealed and cytoskeleton-depleted human red blood cell membrane: A Na-23 multiple quantum filtered and Li-7 NMR relaxation study
Autore:
Srinivasan, C; Minadeo, N; Toon, J; Graham, D; de Freitas, DM; Geraldes, CFGC;
Indirizzi:
Univ Coimbra, Fac Sci & Technol, Dept Biochem, P-3000 Coimbra, Portugal Univ Coimbra Coimbra Portugal P-3000 t Biochem, P-3000 Coimbra, Portugal Loyola Univ, Dept Chem, Chicago, IL 60626 USA Loyola Univ Chicago IL USA 60626 a Univ, Dept Chem, Chicago, IL 60626 USA Univ Coimbra, Ctr Neurosci, P-3000 Coimbra, Portugal Univ Coimbra Coimbra Portugal P-3000 Neurosci, P-3000 Coimbra, Portugal
Titolo Testata:
JOURNAL OF MAGNETIC RESONANCE
fascicolo: 1, volume: 140, anno: 1999,
pagine: 206 - 217
SICI:
1090-7807(199909)140:1<206:CBNALF>2.0.ZU;2-1
Fonte:
ISI
Lingua:
ENG
Soggetto:
PERFUSED RAT-HEART; NUCLEAR MAGNETIC-RELAXATION; HUMAN ERYTHROCYTE-MEMBRANE; INTRACELLULAR SODIUM; EXTRACELLULAR CONTRIBUTION; BIEXPONENTIAL RELAXATION; TRANSVERSE RELAXATION; ARTICULAR-CARTILAGE; 2ND-RANK TENSOR; TQF NMR;
Keywords:
lithium; human red blood cell membranes; cytoskeleton; multiple-quantum-filtered Na-23 NMR; Li-7 relaxation times;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Physical, Chemical & Earth Sciences
Citazioni:
53
Recensione:
Indirizzi per estratti:
Indirizzo: Geraldes, CFGC Univ Coimbra, Fac Sci & Technol, Dept Biochem, POB 3126, P-3000 Coimbra, Portugal Univ Coimbra POB 3126 Coimbra Portugal P-3000 ra, Portugal
Citazione:
C. Srinivasan et al., "Competition between Na+ and Li+ for unsealed and cytoskeleton-depleted human red blood cell membrane: A Na-23 multiple quantum filtered and Li-7 NMR relaxation study", J MAGN RES, 140(1), 1999, pp. 206-217

Abstract

Evidence for competition between Li+ and Na+ for binding sites of human unsealed and cytoskeleton-depleted human red blood cell (csdRBC) membranes was obtained from the effect of added Li+ upon the Na-23 double quantum filtered (DQF) and triple quantum filtered (TQF) NMR signals of Na+-containing red blood cell (RBC) membrane suspensions. We found that, at low ionic strength, the observed quenching effect of Li+ an the Na-23 TQF and DQF signal intensity probed Li+/Na+ competition for isotropic binding sites only. Membrane cytoskeleton depletion significantly decreased the isotropic signal intensity, strongly affecting the binding of Na+ to isotropic membrane sites, but had no effect on Li+/Na+ competition for those sites. Through the observed Na-23 DQF NMR spectra, which allow probing of both isotropic and anisotropic Na+ motion, we found anisotropic membrane binding sites for Na+ when the total ionic strength was higher than 40 mM. This is a consequence of ionic strength effects on the conformation of the cytoskeleton, in particularon the dimer-tetramer equilibrium of spectrin. The determinant involvementof the cytoskeleton in the anisotropy of Na+ motion at the membrane surface was demonstrated by the isotropy of the DQF spectra of csdRBC membranes even at high ionic strength. Li+ addition initially quenched the isotropic signal the most, indicating preferential Li+/Na+ competition for the isotropic membrane sites. High ionic strength also increased the intensity of the anisotropic signal, due to its effect on the restructuring of the membrane cytoskeleton, Further Li+ addition competed with Na+ for those sites, quenching the anisotropic signal. Li-7 T-1 relaxation data for Li+-containing suspensions of unsealed and csdRBC membranes, in the absence and presence of Na+ at low ionic strength, showed that cytoskeleton depletion does not affect the affinity of Na+ for the RBC membrane, but increases the affinity of Li+ by 50%. This clearly indicates that cytoskeleton depletion favors Li+ relative to Na+ binding, and thus Li+/Na+ competition for its isotropic sites. Thus, this relaxation technique proves to be very sensitive to alkali metal binding to the membrane,detecting a more pronounced steric hindrance effect of the cytoskeleton network to binding of the larger hydrated Li+ ion to the membrane phosphate groups. (C) 1999 Academic Press.

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Documento generato il 27/11/20 alle ore 07:30:51