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

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Abstract
The effects of the heavy-metal ions Cd2+ and Zn2+ on the homoeostasis of intracellular free Ca2+ in E367 neuroblastoma cells were examined using 19F-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 μM CdCl2 or 100 μM ZnCl2. Secondly, metal-induced transients in intracellular free Ca2+ were recorded. Addition of 20 μM CdCl2, but not 100 μM 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 μM 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 μM Cd2+ evoked a transient rise in cellular Ins(1,4,5)P3, reaching a maximum level within 5 min after addition of the metal. These results demonstrate that perturbation of the Ins(1,4,5)P3/Ca2+ messenger system is an early and discrete cellular effect of Cd2+.