Transient elevations of cytosolic free calcium retard subsequent apoptosis in neutrophils in vitro.
Elevation of cytosolic calcium ([Ca2+]i) has been reported to induce apoptosis in a number of cell types. However, in the neutrophil, which undergoes apoptosis constitutively during aging in vitro, activation by inflammatory mediators elevates [Ca2+]i and prolongs lifespan via inhibition of apoptosis. To examine this paradox, we investigated the effects of modulation of [Ca2+]i upon apoptosis of neutrophils in vitro. Calcium ionophores (A23187, ionomycin) retarded apoptosis in neutrophil populations after 20 h (P < 0.001). Conversely, intracellular Ca(2+)-chelation, using bis-(o-aminophenoxy)-N,N,N'N'-tetraacetic acid (BAPTA) acetoxymethyl ester (AM) promoted apoptosis (P < 0.02). W-7 (an inhibitor of calmodulin) also promoted apoptosis (P < 0.05). Measurements of [Ca2+]i, using fura-2, showed (a) increased apoptosis in neutrophil populations was not associated with elevated [Ca2+]i, (b) neutrophils cultured with ionophore at concentrations inhibiting apoptosis exhibited transient (< 1 h) elevations of [Ca2+]i, to levels previously reported with receptor-mediated stimuli, and (c) BAPTA was able to prevent the elevation of [Ca2+]i and the inhibition of apoptosis produced by ionophore. Modulation of apoptosis occurred without alterations in intracellular pH. Thus, in the neutrophil, unlike lymphoid cells, elevation of [Ca2+]i exerts an inhibitory effect upon apoptosis. Furthermore, these data suggest that transient elevation of [Ca2+]i elicits signaling events leading to prolonged inhibition of apoptosis.
Whyte
M K
MK
Department of Medicine (Respiratory Division), Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
Hardwick
S J
SJ
Meagher
L C
LC
Savill
J S
JS
Haslett
C
C
D017209:Apoptosis / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004720:Endonucleases / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D009504:Neutrophils / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology
D002147:Calmodulin; D013449:Sulfonamides; D000001:Calcimycin; D004533:Egtazic Acid; D015759:Ionomycin; C017967:W 7; D004720:Endonucleases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium