Mitochondrial metabolic states and membrane potential modulate mitochondrial nitric oxide synthase activity

VALDEZ LB; ZAOBORNYJ T; BOVERIS A

Alba, Italia

Congreso; Joint Meeting of the Oxygen Club of California and the University of Torino, Oxidants and Antioxidants in Biology; 2005

Oxygen Club of California

Mitochondrial nitric oxide synthase (mtNOS) catalyses nitric oxide (NO) production in mitochondria. Coupled respiring mitochondria release NO to the reaction medium; however, the relationship between the rates of NO release and mitochondrial energetics are not clear. The rates of NO production and release and their relationship with mitochondrial membrane potential were determined. The mitochondrial metabolic state regulates the rate of NO release from coupled mitochondria: NO release by heart, liver and kidney mitochondria was about 50% lower in state 3 than in state 4. The ratio of membrane potentials at different pH values significantly correlated with respiratory control and NO release ratios. The decrease in NO release in the state 4-state 3 transition was opposite to what is expected from the matrix acidification of the state 4-state 3 transition and the pH dependence of mtNOS activity: liver and kidney mtNOS show a 57% and 17% higher activity at pH 7.5 (state 3) than at pH 7.8 (state 4). Nitric oxide release and Rh-123 fluorescence were determined in the same experimental conditions: agents that decrease or abolish membrane potential (antimycin or CCCP) minimized NO release (0.48 nmol NO/min. mg protein), while the addition of oligomycin that produces mitochondrial hyperpolarization generated a maximal NO release (1.4 nmol NO/min. mg protein). Nitric oxide release was exponentially associated to membrane potential, and this regulation was marked at the physiological range of membrane potentials. In summary, the evidence reported here sustains the notion of a mitochondria-specific NOS (mtNOS) associated to the inner membrane and regulated by membrane potential.