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 inducti on of apoptosis. To assess the relationship between intracellular zinc conc entration and the rate of apoptosis, cells were grown in media containing 0 .5, 25, or 50 muM zinc and analyzed by flow cytometry or fluorescence micro scopy. Cells grown in 0.5 muM zinc medium over 48 h showed a successive dec rease in intracellular zinc concentration measured by the zinc-specific flu orophore, zinquin. After 18 h in 0.5 muM zinc medium, rhodamine 123 retenti on decreased. However, the addition of 10 muM zinc to the 0.5 muM medium be fore 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 muM zinc mediu m that bound annexin V-FITC. These data indicated that decreased intracellu lar zinc concentration preceded early markers of apoptosis, with alteration s in mitochondrial transmembrane potential preceding the loss of polarity i n the cell membrane.