Meeting Abstract
Mitochondrial coupling represents an animal’s capacity to convert its resources into ATP. Interpretations of mitochondrial coupling depend on whether it is calculated as 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 function (i.e. in rates of respiration to support ATP synthesis and offset leak, and in rate of ATP synthesis) affects these indices of coupling has never been considered in depth. 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 Salma trutta we show that experimental conditions affect mitochondrial coupling, but the pattern observed depends on the measure chosen: a reduction in food availability was associated with an increase in RCR but a decrease in ATP/O ratio in liver mitochondria. Moreover, there was a negative correlation across individuals held in identical conditions between their RCR and their ATP/O ratio, mostly due to dramatic differences in the amount of oxygen required to support ATP synthesis. These results show that the choice of index of mitochondrial coupling can produce different, even opposing, conclusions about the capacity of the mitochondria to produce ATP. Consequently, we encourage investigators to be more specific in their interpretations of these indices, and ideally to validate which index actually predicts animal performance.
