Nitroprusside increases intracellular Zn concentration without affecting cellular thiol content: A model experiment using rat thymocytes and FluoZin-3

Nitric oxide (NO) is cytotoxic under some conditions although it has physiological roles. It is recently proposed that the cytotoxicity of NO is resulted from its interaction with glutathione and zinc. Since we have revealed that a decrease in cellular content of non-protein thiols, presumably glutathione, induces intracellular Zn release, there is a possibility that the cytotoxicity of nitroprusside, a donor of NO, is resulted from the interaction of NO with cellular thiols, leading to an increase in intracellular Zn concentration. To test the possibility, the effects of nitroprusside on cell lethality, intracellular thiol content, and intracellular Zn concentration were examined in rat thymocytes by using a flow cytometer with propidium iodide and FluoZin-3. Nitroprusside at concentrations of 0.3 mM or more (up to 10 mM) significantly augmented FluoZin-3 fluorescence, indicating an increase in intracellular Zn concentration. It was also the case under external Zn-free condition, suggesting nitroprusside-induced release of intracellular Zn. However, nitroprusside at 10 mM did not affect cell lethality and cellular thiol content. Thus, it can be concluded that nitroprusside-induced increase in intracellular Zn concentration is not related to its cytotoxicity.