Combinatorial roles of mitochondria and cGMP/PKG pathway in the generation of neuronal free Zn2+ under the presence of nitric oxide.

Background: Nitric oxide (NO), which possesses both protective and toxic properties, has been observed to have a complicated biphasic character within various types of tissues, including neuronal cells. NO was also found to cause the increase of another important signaling molecular Zn²⁺ (termed as NZR). The molecular mechanism of NZR has been extensively investigated, but the source of Zn²⁺ is present of a major candidate that is yet to be answered. The NO-protein kinase G (PKG) pathway, mitochondria, and metallothioneins (MTs), are all proposed to be the individual source of NZR. However, this hypothesis remains inconclusive. In this study, we examined the function of PKG signaling cascades, the mitochondria storage, and MT-1 during NZR of living PC12 cells. Methods: We applied live-cell imaging in combination with pharmacological inhibitors and activators as well as in vitro Zn²⁺ assay to dissect the functions of the above candidates in NZR. Results: Two mechanisms, namely, mitochondria as the only Zn²⁺ source and the opening of NO-PKG-dependent mitochondrial ATP-sensitive potassium channels (mK^ATP) as the key to releasing NO-induced increase in mitochondrial Zn²⁺, were proven to be the two critical paths of NZR in neuronal-related cells. Conclusion: This new finding provides a reasonable explanation to previously existing and contradictory conclusions regarding the function of mitochondria/mK^ATP and PKG signaling on the molecular mechanism of NZR. [ABSTRACT FROM AUTHOR]