Role of sodium in intracellular calcium elevation and leukotriene B 4 formation by receptor-mediated activation of human neutrophils

Alberto Tedeschi, Paola Ciceri, Simona Zarini, Maurizio Lorini, Manuela Di Donato, Simonetta Nicosia, Antonio Miadonna, Angelo Sala

Research output: Contribution to journalArticlepeer-review

Abstract

The role of Na+ and Na+ exchangers in intracellular Ca2+ elevation and leukotriene B4 (LTBs) formation was investigated in granulocyte macrophage colony-stimulating factor (GM-CSF)-primed, fMLP-stimulated human neutrophils. Isotonic substitution of extracellular Na+ with N-methyl-D-glucamine+ (NMDG +) resulted in over 85% inhibition of the LTBs generation observed (from 14.1±0.9pmol/106 neutrophils to 1.7±1.0pmol/ 106 neutrophils at 0.3μM fMLP). Isotonic substitution of Na + with NMDG+ also induced a significant inhibition of fMLP-induced rise in cytosolic Ca2+ concentration ([Ca 2+]i) (from 2.17- to 0.78-fold increase over basal levels). Pretreatment with an inhibitor of the Na+/Ca2+ exchanger (benzamil) did not inhibit either [Ca2+]i rise or LTBs production, indicating that the observed effects of extracellular Na+-deprivation were unrelated to the Na+/Ca2+ exchanger in receptor-mediated Ca2+ influx, as previously hypothesized. LTBs production by thapsigargin-activated neutrophils was not affected by Na+ depletion, but was totally abolished in the presence of EGTA, suggesting that store depletion-driven extracellular Ca2+ influx is required for leukotriene synthesis and that this process is independent of Na+-deprivation. Exposure to Na+-free medium for the time of GM-CSF priming led to a significant decrease of intracellular pH values, suggesting a role of the Na+/H+ exchanger in intracellular Na+ depletion. Reducing the time of Na+-deprivation totally reversed the observed effect on LTBs production, resulting in enhanced, rather than inhibited, formation of LTBs. These results indicate that LTBs generation and [Ca2+]i rise in human neutrophils primed by GM-CSF and stimulated with fMLP is dependent on intracellular Na+ concentration, and, at variance with previously published results, unrelated to the Ca2+ influx through the Na+/Ca2+ exchanger.

Original languageEnglish
Pages (from-to)385-393
Number of pages9
JournalBiochemical Pharmacology
Volume67
Issue number2
DOIs
Publication statusPublished - Jan 15 2004

Keywords

  • Calcium ion
  • Leukotriene B
  • Neutrophils
  • Sodium ion

ASJC Scopus subject areas

  • Pharmacology

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