A decrease in intracellular zinc level precedes the detection of early indicators of apoptosis in HL-60 cells

Low extracellular zinc concentrations have been associated with the induction of apoptosis. To assess the relationship between intracellular zinc concentration and the rate of apoptosis, cells were grown in media containing 0.5, 25, or 50 microM zinc and analyzed by flow cytometry or fluorescence microscopy. Cells grown in 0.5 microM zinc medium over 48 h showed a successive decrease in intracellular zinc concentration measured by the zinc-specific fluorophore, zinquin. After 18 h in 0.5 microM zinc medium, rhodamine 123 retention decreased. However, the addition of 10 microM zinc to the 0.5 microM medium before 16 h in culture restored rhodamine retention in the cells. After 30 h there was an increase in the number of cells cultured in 0.5 microM zinc medium that bound annexin V-FITC. These data indicated that decreased intracellular zinc concentration preceded early markers of apoptosis, with alterations in mitochondrial transmembrane potential preceding the loss of polarity in the cell membrane.