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

• Published in: Biochemical pharmacology Vol. 67; no. 2; pp. 385 - 393
• Main Authors: Tedeschi, Alberto, Ciceri, Paola, Zarini, Simona, Lorini, Maurizio, Di Donato, Manuela, Nicosia, Simonetta, Miadonna, Antonio, Sala, Angelo
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15-01-2004
• Subjects: Calcium ion; Leukotriene B 4; Neutrophils; Sodium ion; Leukotriene B 4; 5-LO; Calcium ion; GM-CSF; NMDG; Sodium ion; Neutrophils; [Ca 2+] i; LTBs
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/j.bcp.2003.09.019

The role of Na
+ and Na
+ exchangers in intracellular Ca
2+ elevation and leukotriene B
4 (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±0.9
pmol/10
6 neutrophils to 1.7±1.0
pmol/10
6 neutrophils at 0.3
μM fMLP). Isotonic substitution of Na
+ with NMDG
+ also induced a significant inhibition of fMLP-induced rise in cytosolic Ca
2+ concentration ([Ca
2+]
i) (from 2.17- to 0.78-fold increase over basal levels). Pretreatment with an inhibitor of the Na
+/Ca
2+ exchanger (benzamil) did not inhibit either [Ca
2+]
i rise or LTBs production, indicating that the observed effects of extracellular Na
+-deprivation were unrelated to the Na
+/Ca
2+ exchanger in receptor-mediated Ca
2+ 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 Ca
2+ 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 [Ca
2+]
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 Ca
2+ influx through the Na
+/Ca
2+ exchanger.