Comparison between sodium-hydrogen ion and lithium-hydrogen ion exchange in human platelets

Oscar A. Gende, Horacio E. Cingolani

Research output: Contribution to journalArticlepeer-review

Abstract

The membrane-coupled exchange of Li+ and/or Na+ for H+ was studied in human platelets measuring intracellular pH (pHi) with a fluorescent indicator. A Li+-containing medium restored the internal pH of preacidified platelets to their prior pHi control value. When Na+ was replaced by Li+, similar steady-state values were attained in this system, although it was transported more slowly. The Km and Vmax were both higher with Na+ than with Li+. Exchanges of Li+ or Na+ with H+ were both blocked by ethylisopropylamiloride (EIPA) achieving half-maximal inhibition at submicromolar concentrations. The efflux of H+ ions exchanged by Li+ or Na+ was reversible: platelets preloaded with Li+ or Na+ and resuspended in a choline medium exhibited an influx of H+ sensitive to EIPA. Thrombin, an activator of Na+/H+ exchange, induced a rapid increase in platelet internal pH in the presence of exogenous Li+. Thus: (1) Li+ can be substituted for Na+ in both the forward and the reverse exchange reaction; (2) Li+, while having a higher affinity than Na+ for the external site of the membrane carrier, has a lower Km and (3) Li+ as well as Na+ exchange are activated by thrombin.

Original languageEnglish (US)
Pages (from-to)219-224
Number of pages6
JournalBBA - Biomembranes
Volume1152
Issue number2
DOIs
StatePublished - Nov 7 1993

Keywords

  • (Platelet)
  • Amiloride derivative
  • Intracellular pH
  • Lithium-hydrogen ion exchange
  • Sodium-hydrogen ion exchange
  • Thrombin activation

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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