NOR-3, a donor of nitric oxide, increases intracellular Zn²⁺ concentration and decreases cellular thiol content: A model experiment using rat thymocytes, FluoZin-3, and 5-chloromethylfluorescein

Our previous study showed that nitroprusside, a donor of nitric oxide (NO), increased intracellular Zn2+ concentration without affecting cellular content of glutathione (GSH) although it has been proposed that the cytotoxicity of NO is resulted from its interaction with glutathione and zinc. Nitroprusside releases not only NO but also cyanides (Fe(II)CN and Fe(III)CN), CN-, Fe2+, and Fe3+. Therefore, such decomposition products may mask NO-induced action on cellular GSH content. In this study, we used NOR-3 as a donor of NO to reveal the effects of NO on intracellular Zn2+ concentration and cellular GSH content in a cytometric manner with fluorescent probes, FluoZin-3-AM and 5-chloromethylfluorescein diacetate. NOR-3 at 1-3 mM significantly increased intracellular Zn2+ concentration and decreased cellular GSH content. After the removal of extracellular Zn2+ by diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA, a chelator for Zn2+), the increase in intracellular Zn2+ concentration by NOR-3 was still observed although DTPA significantly attenuated the increase in intracellular Zn2+ concentration by NOR-3. Results suggest an involvement of both intracellular Zn2+ release and increase in membrane Zn2+ permeability. It is likely that NO induces oxidative stress, leading to an increase in intracellular Zn2+ concentration.