Na+-H+ and Na+-Li+ exchange are mediated by the same membrane transport protein in human red blood cells

An NMR investigation

Yuling Chi, Suilan Mo, Duarte Mota De Freitas

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Na+-H+ exchange is a transport system present in erythrocytes which plays an important role in the regulation of intracellular pH, cellular volume, and transmembrane ion transport. Na+-Li+ exchange has received much attention and has been investigated in more detail than have any of the other ion transport systems, because of its high reproducibility. Both red blood cell (RBC) Na+-H+ and Na+-Li+ exchange are elevated in essential hypertensive patients relative to normotensive individuals. RBC Na+-Li+ exchange may be a mode of operation of Na+-H+ exchange. Amiloride and its analogue, 5-(N,N-hexamethylene)amiloride (HMA), are well-known inhibitors of Na+- H+ exchange, whereas phloretin strongly inhibits Na+-Li+ exchange. In this study, we tested the effects of amiloride, HMA, and phloretin on Na+-Li+ exchange activity in intact RBCs by using atomic absorption. We investigated by using 7Li nuclear magnetic resonance (NMR) spectroscopy the effects of HMA and phloretin inhibition on Li+ efflux across resealed H+- and Li+-loaded RBC ghosts in the absence and presence of pH gradients. Amiloride inhibitory activities on both Na+ and Li+ binding to exposed RBC membranes under different pH conditions were also studied by 23Na and 7Li NMR relaxation time measurements. We found that Na+-Li+ exchange activity was inhibited by amiloride, HMA, and phloretin in suspensions of intact RBCs and of resealed RBC ghosts. Li+ efflux rates across resealed H+- and Li+- loaded RBC ghosts were significantly lower when a pH gradient was present, presumably because of the competition between Li+ and H+ for transport by the same transport protein. Amiloride had similar inhibitory constants on both Na+ and Li+ binding to RBC membranes (102 ± 48 M-1 vs 964 ± 40M- 1 at pH 8.0; 731 ± 147 M-1 m vs 716 ± 27 M-1 at pH 7.0). These results suggest that Na+-H+ exchange and Na+-Li+ exchange are mediated by the same RBC membrane transport protein.

Original languageEnglish (US)
Pages (from-to)12433-12442
Number of pages10
JournalBiochemistry
Volume35
Issue number38
DOIs
StatePublished - 1996
Externally publishedYes

Fingerprint

Membrane Transport Proteins
Blood
Magnetic Resonance Spectroscopy
Erythrocytes
Cells
Nuclear magnetic resonance
Phloretin
Amiloride
Cell membranes
Erythrocyte Membrane
Proton-Motive Force
Ion Transport
Ions
Cell Membrane
Time measurement
Relaxation time
Nuclear magnetic resonance spectroscopy
Suspensions
Carrier Proteins
Membrane Proteins

ASJC Scopus subject areas

  • Biochemistry

Cite this

Na+-H+ and Na+-Li+ exchange are mediated by the same membrane transport protein in human red blood cells : An NMR investigation. / Chi, Yuling; Mo, Suilan; De Freitas, Duarte Mota.

In: Biochemistry, Vol. 35, No. 38, 1996, p. 12433-12442.

Research output: Contribution to journalArticle

Chi, Yuling ; Mo, Suilan ; De Freitas, Duarte Mota. / Na+-H+ and Na+-Li+ exchange are mediated by the same membrane transport protein in human red blood cells : An NMR investigation. In: Biochemistry. 1996 ; Vol. 35, No. 38. pp. 12433-12442.
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