Membrane potential modulates mtNOS activity and NO diffusion to the cytosol

VALDEZ LB; ZAOBORNYJ T; BOVERIS A

Santa Bárbara, California, USA

Congreso; Annual Meeting of Oxygen Club of California. 2004 World Congress: Oxidants & Antioxidants in Biology; 2006

Oxygen Club of California

Membrane potential modulates mtNOS activity and NO diffusion to the cytosol Laura B. Valdez, Tamara Zaobornyj and Alberto Boveris Laboratory of Free Radical Biology, School of Pharmacy and Biochemistry, University of Buenos Aires. Buenos Aires, Argentina. lbvaldez@ffyb.uba.ar   Mitochondrial metabolic state regulates the rate of NO production from heart, liver and kidney mitochondria. NO release by heart mitochondria was about 45% lower in state 3 (1.22 ± 0.05 nmol/min.mg protein) than in state 4 (2.23 ± 0.06 nmol/min.mg protein). In the state 4-state 3 transition the activity of mtNOS, responsible for NO release, is driven by the membrane potential and not by intramitochondrial pH changes. NO release by rat liver mitochondria showed an exponential dependence on membrane potential: agents that decrease or abolish membrane potential, minimize NO release; while the addition of oligomycin, that produces mitochondrial hyperpolarization, generates the maximal NO release. A similar behavior was reported for heart mitochondrial H2O2 production (Korshunov et al., 1997). The fraction of cytosolic NO provided by diffusion from mitochondria was 61% in heart, 47% in liver, and 30% in kidney. The intramitochondrial concentrations of L-arginine and NADPH are higher than their KM values, and the changes in their concentrations in the state 4-state 3 transition are not enough to explain the changes in NO release. These data indicate that the redox state of the respiratory chain components regulates H2O2 production and Dy modulates NO release, and support the speculation that NO and H2O2 report a high mitochondrial energy charge to the cytosol. The regulation of mtNOS activity, an apparently voltage-dependent enzyme, at the physiological range of membrane potentials, makes mtNOS a regulable enzyme that in turn regulates mitochondrial O2 uptake and H2O2 production.