Flux of intracellular labile zinc during apoptosis (gene-directed cell death) revealed by a specific chemical probe, Zinquin

Background: The transition metal Zn(II) is thought to regulate cell and tissue growth by enhancing mitosis (cell proliferation) and suppressing the counterbalancing process of apoptosis (gene-directed cell death). To investigate the role of Zn(II) further, we have used a UV-excitable Zn(II)-specific fluorophore, Zinquin. The ester group of Zinquin is hydrolyzed by living cells, ensuring its intracellular retention; this allows the visualization and measurement of free or loosely-bound (labile) intracellular Zn(II) by fluorescence video image analysis or fluorimetric spectroscopy. Results: Here we show that in cells undergoing early events of apoptosis, induced spontaneously or by diverse agents, there is a substantial increase in their Zinquin detectable Zn(II).This increase occurred in the absence of exogenous Zn(II) and before changes in membrane permeability, consistent with a release of Zn(II) from intracellular stores or metalloproteins rather than enhanced uptake from the medium.We propose that there is a major redistribution of Zn(II) during the induction of apoptosis, which may influence or precipitate some of the later biochemical and morphological changes. Conclusions: The phenomenon of Zn(II) mobilization, revealed by Zinquin, presents a new element in the process of apoptosis for investigation and may permit rapid and sensitive identification of apoptotic cells, particularly in those tissues where their frequency is low.