Study of the interactions of cadmium and zinc ions with cellular calcium homoeostasis using F-19-NMR spectroscopy

The effects of the heavy-metal ions Cd2+ and Zn2+ on the homoeostasis of intracellular free Ca2+ in E367 neuroblastoma cells were examined using F-19-NMR spectroscopy with the fluorinated chelator probe 1,2-bis-(2-amino-5-fluorophenoxy)-ethane-N,N,N',N'-tetra-acetic acid (5F-BAPTA). First, the technique was used to quantify the uptake and intracellular free concentrations of the heavy metals after treatment of the cells with 20 mu M CdCl2 or 100 mu M ZnCl2. Secondly, metal-induced transients in intracellular free Ca2+ were recorded. Addition of 20 mu M CdCl2, but not 100 mu M ZnCl2, evoked a transient increase in Ca2+ from a resting level of 84 nM to approx. 190 nM within 15 min after addition of the metal. Zn2+ at 20 mu M completely prevented the induction of a Ca2+ transient by Cd2+. Ca2+ was mobilized by Cd2+ from intracellular organelles, since depletion of these stores, by thapsigargin abolished the effect of the toxic metal. Furthermore, 20 mu M Cd2+ evoked a transient rise in cellular Ins(1,4,5)P-3, reaching a maximum level within 5 min after addition of the metal. These results demonstrate that perturbation of the Ins(1,4,5)P-3/Ca2+ messenger system is an early and discrete cellular effect of Cd2+.