Role of sodium in intracellular calcium elevation and leukotriene B4 formation by receptor-mediated activation of human neutrophils.
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+/-0.9pmol/10(6) neutrophils to 1.7+/-1.0pmol/10(6) neutrophils at 0.3 microM 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.
Tedeschi
Alberto
A
Allergy and Immunopharmacology Unit, First Division of Internal Medicine, IRCCS Ospedale Maggiore Policlinico, Milan, Italy.
Ciceri
Paola
P
Zarini
Simona
S
Lorini
Maurizio
M
Di Donato
Manuela
M
Nicosia
Simonetta
S
Miadonna
Antonio
A
Sala
Angelo
A
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007975:Leukotriene B4 / Q000096:biosynthesis*; D009504:Neutrophils / Q000378:metabolism*; D012964:Sodium / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors
D017923:Sodium-Hydrogen Exchangers; D007975:Leukotriene B4; D012964:Sodium; D002118:Calcium