Role of Mitochondrial NO/cGMP/PKG Signaling System in the Activation and Inhibition of Mitochondrial Respiration by L-Arginine and NO Donors
The involvement of the mitochondrial calcium-dependent NO synthase (mtNOS) in the regulation of mitochondrial respiration has not been sufficiently studied. Moreover, possible functioning of mitochondrial signaling system involving mtNOS/guanylate cyclase (GC)/kinase G (PKG) and the impact of this system (mtNOS/GC/PKG-SS) on mitochondrial respiration have not yet been analyzed. To investigate this issue, we performed experiments on isolated rat liver and heart mitochondria using specific inhibitors of NOS, GC, and PKG. Mitochondrial respiration was supported by pyruvate and glutamate or succinate. It was shown that L-arginine and NO donor SNP exert concentration-dependent effects on the mitochondrial respiration activated by ADP in the presence of hexokinase and glucose. At low concentrations, L-arginine (3–100 μM) and SNP (3–100 μM) activated mitochondrial respiration. NOS, GC, and PKG inhibitors eliminated this effect, indicating that mtNOS/GC/PKG-SS is involved in the activation of the respiration. At high concentrations, L-arginine and SNP, by contrast, inhibited respiration. Under these conditions, inhibitors of the mtNOS/GC/PKG-signaling system enhanced the inhibition of respiration evoked by L-arginine or SNP, which indicates an opposite effect of the excess NO and PKG on the mitochondrial respiration. The results suggest that the functioning of calcium-dependent mtNOS/GC/PKG-SS can ensure the activation of respiration at low concentrations of L-arginine or the NO donor SNP in the medium.