Effect of exogenous and endogenous nitric oxide on mitochondrial respiration of rat hepatocytes

Although nitric oxide (·N = O) biosynthesis is inducible in rat hepatocytes (HC), the physiological significance of ·N = O production by these cells is unknown. Short exposure of HC to authentic ·N = O led to a concentration-dependent inhibition of mitochondrial aconitase, NADH-ubiquinone oxidoreductase, and succinate-ubiquinone oxidoreductase (complexes I and II of the mitochondrial electron transport chain). Most susceptible to ·N = O inhibition was mitochondrial aconitase, in which a reduction in enzyme activity to 20.2 ± 1.6% of control was observed. In contrast to mitochondrial aconitase, cytosolic aconitase activity was not inhibited by ·N = O. After exposure to a maximal inhibitory concentration of ·N = O, mitochondrial aconitase activity recovered completely within 6 h. Complex I did not fully recover within this incubation period. Endogenous ·N = O biosynthesis was induced in HC by a specific combination of cytokines and lipopolysaccharide. After 18 h of incubation with these stimuli, a significant inhibition of mitochondrial aconitase activity to 70.8 ± 2.4% of controls was detected. However, this was due only in part to the action of ·N = O. A non-·N = O-dependent inhibition of mitochondrial function appeared to be mediated by tumor necrosis factor.