Nitroprusside increases intracellular Zn2+ 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
Zn2+ 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 Zn2+ concentration. To test the
possibility, the effects of nitroprusside on cell lethality, intracellular thiol content, and intracellular Zn2+
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 Zn2+ concentration. It was also the case under external
Zn2+-free condition, suggesting nitroprusside-induced release of intracellular Zn2+. 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 Zn2+ concentration is not related to its cytotoxicity.