The effect of cellular age on zinc levels in untreated and zinc-treated human diploid fibroblasts.

Cellular aging is accompanied by increased cellular permeability to zinc(II). The intrinsic zinc content of human diploid fibroblast cells increases with cell age, so that it quadruples from early to late passage, on a Zn(II) per cell or per cell volume basis, but it remains constant on a Zn(II) per protein basis. When the cells are challenged with toxic concentrations (0.2 mM) of Zn(II), both the rate of zinc incorporation into the cells and the amount of zinc incorporated at equilibrium increases considerably with age (unless measured as zinc per protein). In terms of growth inhibition, Zn(II) is more toxic to the cell than Cu(II), Mn(II), or Mg(II).