Salin 2018 Integr Comp Biol

Salin K, Villasevil EM, Anderson GJ, Selman C, Chinopoulos C, Metcalfe NB (2018) The RCR and ATP/O indices can give contradictory messages about mitochondrial efficiency. Integr Comp Biol 58:486-94.

» PMID: 29982616 Open Access

Salin K, Villasevil EM, Anderson GJ, Selman C, Chinopoulos C, Metcalfe NB (2018) Integr Comp Biol

Abstract: Mitochondrial efficiency is typically taken to represent an animal's capacity to convert its resources into ATP. However, the term mitochondrial efficiency, as currently used in the literature, can be calculated as either the respiratory control ratio, RCR (ratio of mitochondrial respiration supporting ATP synthesis to that required to offset the proton leak) or as the amount of ATP generated per unit of oxygen consumed, ATP/O ratio. The question of how flexibility in mitochondrial energy properties (i.e. in rates of respiration to support ATP synthesis and offset proton leak, and in the rate of ATP synthesis) affects these indices of mitochondrial efficiency has tended to be overlooked. Furthermore, little is known of whether the RCR and ATP/O ratio vary in parallel, either among individuals or in response to environmental conditions. Using data from brown trout Salmo trutta we show that experimental conditions affect mitochondrial efficiency, but the apparent direction of change depends on the index chosen: a reduction in food availability was associated with an increased RCR (i.e. increased efficiency) but a decreased ATP/O ratio (decreased efficiency) in liver mitochondria. Moreover, there was a negative correlation across individuals held in identical conditions between their RCR and their ATP/O ratio. These results show that the choice of index of mitochondrial efficiency can produce different, even opposing, conclusions about the capacity of the mitochondria to produce ATP. Neither ratio is necessarily a complete measure of efficiency of ATP production in the living animal (RCR because it contains no assessment of ATP production, and ATP/O because it contains no assessment of respiration to offset the proton leak). Consequently, we suggest that a measure of mitochondrial efficiency obtained nearer to conditions where respiration simultaneously offsets the proton leak and produce ATP would be sensitive to changes in both proton leakage and ATP production, and is thus likely to be more representative of the state of the mitochondria in vivo.

• Bioblast editor: Kandolf G • O2k-Network Lab: UK Glasgow Metcalfe NB, FR Plouzane Salin K, HU Budapest Chinopoulos C

Comments

Gnaiger E 2022-02-15

• "However, the term mitochondrial efficiency, as currently used in the literature, can be calculated as either the respiratory control ratio, RCR (ratio of mitochondrial respiration supporting ATP synthesis to that required to offset the proton leak) or as the amount of ATP generated per unit of oxygen consumed, ATP/O ratio." - This reference to 'the term mitochondrial efficiency, as currently used in the literature' ignores the entire literature on physical chemistry, chemical engineering, and the thermodynamics of irreversible processes - more specifically: all the literature on (biological) thermodynamics. To avoid confusion of terms, (1) the classical RCR should not be referred to as an expression of efficiency, because it is a ratio of respiratory fluxes without consideration of forces, and likewise (2) the ATP/O ratio is a flux ratio. Flux efficiencies and force efficiencies are properly normalized to obtain maximum efficiencies of 1 (or 100 %). This is established in the current literature. » Ergodynamic efficiency

• ".. has tended to be overlooked" - In fact, it has been overlooked by the authors, by ignoring the pertinent literature.

• "little is known of whether the RCR and ATP/O ratio vary in parallel" - A complete analysis is available:

Gnaiger E (2001) Bioenergetics at low oxygen: dependence of respiration and phosphorylation on oxygen and adenosine diphosphate supply. Respir Physiol 128:277-97. - »Bioblast link«

• "the choice of index of mitochondrial efficiency can produce different, even opposing, conclusions about the capacity of the mitochondria to produce ATP" - Yes, even if you use 1/RCR instead of RCR, this apparently 'opposing' effect emerges. Do the authors turn a mathematical triviality into a trivial biological terminology?

Cited by

• Cardoso et al (2021) Magnesium Green for fluorometric measurement of ATP production does not interfere with mitochondrial respiration. Bioenerg Commun 2021.1. doi:10.26124/bec:2021-0001

Labels: MiParea: Respiration, Comparative MiP;environmental MiP, mt-Awareness 

Organism: Fishes  Tissue;cell: Liver  Preparation: Homogenate 

Regulation: ATP production  Coupling state: LEAK, OXPHOS  Pathway: N, S, NS, ROX  HRR: Oxygraph-2k 

Labels, 2018-08, MgG, MitoFit 2021 MgG