MITOCHONDRIAL RESPIRATION IN LOCUST FLIGHT MUSCLES

Highly coupled mitochondria isolated from locust flight muscles display substrate preferences consistent with the use of carbohydrate and lipid as the major metabolic fuels during flight. Maximal rates of coupled respiration expressed per milligram mitochondrial protein exceed by severalfold published values obtained using vertebrate muscle mitochondria. These differences in maximal rates of coupled respiration in vitro are apparent even when rates are expressed per unit mitochondrial marker enzyme (citrate synthase) activity or per unit mitochondrial volume (exchangeable water space). Locusts in flight achieve a greater fraction of the flux measured in vitro through cytochrome oxidase than mammals exercising at maximum aerobic capacity. These data suggest that besides possessing "better" mitochondria, locusts may possess higher capacities for O2 (and/or substrate) delivery, allowing the achievement of higher rates of respiration in vivo than in mammals.