Abstract 16529: Coupling of Mitochondrial Respiration and Superoxide Production in Healthy and Failing Hearts
Mitochondrial respiration through electron transport chain (ETC) activity critically regulates energy homeostasis and heart performance. Insufficient energy supply and excessive oxidative stress underlie the mechanism of heart failure. How mitochondrial respiration and reactive oxygen species production are fine-tuned in the healthy heart and dys-regulated in the failing heart remain largely unknown. Recently, we discovered stochastic and transient superoxide production events, named superoxide flashes, in single mitochondria of intact cardiac myocytes. Here, we show that superoxide flash is tightly coupled to mitochondrial respiration and diminished superoxide flash activity is a hallmark of the transition to heart failure. Increase in either metabolic substrate availability (glucose 10 mM, palmitate 0.5 mM, or pyruvate 10 mM) or energy demand (isoproterenol 1 µM or pacing) boosted superoxide flash activity. In permeabilized myocytes, addition of the specific substrates for each ETC complex (Complex I, II or IV) elevated superoxide flash activity 3-4 folds over basal level, indicating that superoxide flash arises from the ETC electron flow. Further, myocytes from a Complex I deficient mice (Ndufs4H-/-) showed significantly lower flash activity, which was stimulated by palmitate but not pyruvate. This indicates that Complex I is likely the primary site for electron entrance under normal conditions. However, when Complex I activity is compromised, electron entrance at other sites (associated with palmitate oxidation) may be enhanced. Interestingly, inhibition of the FoF1 ATP synthase by oligomycin A acutely increased flash activity followed by a decline to below normal level. Thus, ETC activity is transiently accelerated upon blockade of the downstream ATP generation. In the pressure overload induced heart failure model, the decline of superoxide flash precedes the contractile dysfunction, suggesting that impaired mitochondrial respiration occurs at the early stage of heart failure. In summary, our data support the mechanistic coupling of superoxide flash with mitochondrial respiration, and suggest that superoxide flash is a sensitive indication of single mitochondrial dysfunction in heart failure.
- © 2012 by American Heart Association, Inc.