Elevations in cytosolic free Ca2+ are not required to trigger apoptosis in human leukaemia cells.
Previous studies have indicated that Ca2+ is a trigger for apoptosis (programmed cell death) in thymocytes and related cell lines. Recently we have shown that levels of apoptosis in leukaemic cells are diminished in Ca(2+)-deficient conditions, indicating that Ca2+ may be important in the mechanism of apoptosis in these cells. In the present study we investigated the possibility that Ca2+ serves as a trigger for apoptosis in the human leukaemic cell line, HL-60. Using fura-2 to measure cytosolic free Ca2+ concentrations, [Ca2+]i, in cell suspensions, and by using ratio imaging of fura-2 in single cells, we did not observe an early significant increase in [Ca2+]i in HL-60 cells undergoing apoptosis. The latter stages of apoptosis were, however, accompanied by increasing [Ca2+]i; these increases were apparently a result of, rather than a cause of, apoptosis. Furthermore, apoptosis could be induced in HL-60 cells under conditions of vastly reduced [Ca2+]i achieved by loading these cells with fura-2 in the presence of EGTA. These results indicate that elevation of [Ca2+]i is not a prerequisite for apoptosis in HL-60 cells and that apoptosis can occur in these cells in the presence of low [Ca2+]i.
Lennon
S V
SV
Department of Biology, St Patrick's College, Maynooth, Co. Kildare, Republic of Ireland.
Kilfeather
S A
SA
Hallett
M B
MB
Campbell
A K
AK
Cotter
T G
TG
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects / Q000528:radiation effects; D003600:Cytosol / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000032:analysis; D004587:Electrophoresis, Agar Gel; D000431:Ethanol / Q000494:pharmacology; D016257:Fura-2 / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism / Q000473:pathology*; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays
D004273:DNA, Neoplasm; D000001:Calcimycin; D000431:Ethanol; D006861:Hydrogen Peroxide; D002118:Calcium; D016257:Fura-2