bims-resufa 2019-04-21 papers

Issue of 2019–04–21
two papers selected by
Vera Strogolova, Marquette University

Nitric Oxide. 2019 Apr 15. pii: S1089-8603(18)30315-X. [Epub ahead of print]

The effect of nitric oxide on mitochondrial respiration.

Juan José Poderoso, Katia Helfenberger, Cecilia Poderoso.

This article reviews the interactions between nitric oxide (NO) and mitochondrial respiration. Mitochondrial ATP synthesis is responsible for virtually all energy production in mammals, and every other process in living organisms ultimately depends on that energy production. Furthermore, both necrosis and apoptosis, that summarize the main forms of cell death, are intimately linked to mitochondrial integrity. Endogenous and exogenous •NO inhibits mitochondrial respiration by different well-studied mechanisms and several nitrogen derivatives. Instantaneously, low concentrations of •NO, specifically and reversibly inhibit cytochrome c oxidase in competition with oxygen, in several tissues and cells in culture. Higher concentrations of •NO and its derivatives (peroxynitrite, nitrogen dioxide or nitrosothiols) can cause irreversible inhibition of the respiratory chain, uncoupling, permeability transition, and/or cell death. Peroxynitrite can cause opening of the permeability transition pore and opening of this pore causes loss of cytochrome c, which in turn might contribute to peroxynitrite-induced inhibition of respiration. Therefore, the inhibition of cytochrome c oxidase by •NO may be involved in the physiological and/or pathological regulation of respiration rate, and its affinity for oxygen, which depend on reactive nitrogen species formation, pH, proton motriz force and oxygen supply to tissues.

Keywords: Cellular respiration; Cytochrome c oxidase; Mitochondria; Nitric oxide

DOI: https://doi.org/10.1016/j.niox.2019.04.005

FEBS Open Bio. 2019 Apr;9(4): 571-581

Mitochondrial matrix pH acidifies during anoxia and is maintained by the F1Fo-ATPase in anoxia-tolerant painted turtle cortical neurons.

Peter John Hawrysh, Leslie Thomas Buck.

The western painted turtle (Chrysemys picta bellii) can survive extended periods of anoxia via a series of mechanisms that serve to reduce its energetic needs. Central to these mechanisms is the response of mitochondria, which depolarize in response to anoxia in turtle pyramidal neurons due to an influx of K+. It is currently unknown how mitochondrial matrix pH is affected by this response and we hypothesized that matrix pH acidifies during anoxia due to increased K+/H+ exchanger activity. Inhibition of K+/H+ exchange via quinine led to a collapse of mitochondrial membrane potential (Ψm) during oxygenated conditions in turtle cortical neurons, as indicated by rhodamine-123 fluorescence, and this occurred twice as quickly during anoxia which indicates an elevation in K+ conductance. Mitochondrial matrix pH acidified during anoxia, as indicated by SNARF-1 fluorescence imaged via confocal microscopy, and further acidification occurred during anoxia when the F1Fo-ATPase was inhibited with oligomycin-A, indicating that ΔpH collapse is prevented during anoxic conditions. Collectively, these results indicate that the mitochondrial proton electrochemical gradient is actively preserved during anoxia to prevent a collapse of Ψm and ΔpH.

Keywords: Chrysemys picta bellii; F1Fo‐ATPase; K+/H+ exchanger; SNARF‐1; anoxia; channel arrest; mitochondria

DOI: https://doi.org/10.1002/2211-5463.12612