Change of zinc uptake under growth arrest and apoptosis.

Zinc uptake is critical for cell proliferation. On the basis of the evidence that brain tumors are positively-imaged with 65Zn, cellular zinc uptake was studied under growth arrest and apoptosis to understand the relationship between cellular viability and zinc uptake. When NIH3T3 cells were cultured in albumin-coated dishes under the presence of serum, the viability of the cells detached from the extracellular matrix, which was determined with fluoresceine diacetate, was almost the same as the control cells cultured in untreated dishes. Both the uptake of 14C-thymidine and 65Zn by the cells was significantly suppressed by detachment from the extracellular matrix, suggesting that cellular zinc uptake is suppressed by growth arrest. When apoptosis was induced in the cells detached from the extracellular matrix under serum-free condition, 65Zn uptake by the cells led to apoptosis which was significantly higher than that by the control cells. 65Zn uptake by C6 glioma cells, which were irradiated with gamma-ray, was also higher than that by control (unirradiated) C6 glioma cells. The present study demonstrates that zinc uptake is involved not only in the process of cell proliferation, but also in the process of apoptosis.