Abstract
Background/Aims Numerous studies have shown that cytosolic second messengers nitric oxide (NO) and cGMP and protein kinase G (PKG1) play important role in regulating cell viability by modulating mitochondrial permeability transition pore (MPTP) opening, necrotic and apoptotic cell death. The involvement of mitochondrial calcium-dependent NO-synthase (mtNOS) in the control of MPTP is much less explored. Moreover, possible functioning of mitochondrial mtNOS/guanylate cyclase (GC)/PKG-signaling system (mtNOS/PKG-SS) and its impact on mitochondrial respiration and MPTP have not been analyzed yet.
Methods To address the issue we performed the experiments on isolated rat liver mitochondria with the application of specific inhibitors of NOS, GC and PKG. Mitochondrial respiration was supported by pyruvate and glutamate or succinate plus rotenone in the presence of hexokinase and ADP.
Results Obtained results indicate that L-arginine and NO-donors (SNP, SNAP) produce bidirectional concentration-dependent effects on mitochondrial respiration and on MPTP opening evoked by calcium ions or palmitoylcarnitine excess. In low concentrations L-arginine (10 to 200 μM) and NO-donors (10 to 50 μM) activate the respiration and raise threshold concentrations of calcium and palmitoylcarnitine, required for dissipation of mitochondrial membrane potential and pore opening. The inhibitors of NOS, GC and PKG eliminate both effects, what disclose the involvement of mtNOS/PKG-SS in the activation of respiration and deceleration of MPTP opening. In high concentrations L-arginine and NO-donors inhibit the respiration and promote MPTP opening. Observed alteration in the direction of L-arginine and NO-donors effects suggests that the inhibition evoked by mitochondrial NO excess may dominate over the protection afforded by mtNOS/PKG-SS.
Conclusions These findings demonstrate that the functioning of calcium-dependent mtNOS/PKG-SS, involved in complex calcium and NO interplay, might provide feedforward activation of the respiration and lowering the sensitivity of MPTP to calcium and palmitoylcarnitine excess.