Selection and partial characterization of calcium ionophore (A23187) resistant cells

We have selected calcium ionophore (A23187)-resistant cells (AR-7) in a human promyelocytic leukemia cell line, HL-60. AR-7 showed approximately 8.5-fold resistance to A23187 compared with the wild type cells after continuous exposure for 3 days. AR-7 had cross resistance to ionomycin (4.6-fold) and thapsigargin (340-fold) which can also increase intracellular Ca++. Similar magnitude of resistance to apoptosis, as defined by characteristic morphology and internucleosomal DNA fragmentation, induced by these agents was observed after 4 hr of incubation. However, both the elevation of intracellular Ca++ following stimulation with various concentrations of A23187 and the sensitivity to anti-cancer agents including etoposide, 1-beta-D arabinofuranosylcytosine, and hydroxyurea were comparable between the two cell types. This cell line is considered to be useful for exploring the mechanism(s) of cell death, especially apoptosis, induced by calcium ionophore.