The effects of age and acclimation temperature on mitochondrial ROS production, respiration, and structure in western painted turtles (Chrysemys picta bellii)

In mammalian hearts, reperfusion upsurges reactive oxygen species (ROS) production via succinate-driven reverse electron transport (RET). Yet, the adult painted turtle, which can survive ~170 days of anoxia at 3°C, shows an ability to avoid damage upon reoxygenation, making it an ideal model to study this clinically relevant insult. The hatchling is less anoxia-tolerant, surviving ~40 days at 3°C, and its handling of ROS production during reoxygenation may reflect this difference in anoxia tolerance. Our objective was to better the influence of development on mitochondrial ROS production and respiration in adult and hatchling painted turtles. Because reoxygenation naturally occurs during cold temperatures, when turtles emerge from overwintering in anoxic ponds, we also examined the effects of cold acclimation on mitochondrial function. To test the hypotheses that cold acclimation decreases mitochondrial respiration more in adults than hatchlings, and that hatchlings show a higher rate of maximal reactive oxygen species production, turtles of both age groups were acclimated to 20°C and 3°C, and ROS production of isolated cardiac ventricular mitochondria was measured during succinate-driven RET. Respiration rates were also measured with pyruvate/malate, palmitoylcarnitine, glutamate and succinate. Samples from the 20°C group were fixed in glutaraldehyde, embedded in epoxy, and sectioned onto grids for imaging using transmission electron microscopy (TEM). Our results showed that hatchlings had lower rates of succinate-induced ROS production via RET and State III respiration compared to adults. Cold acclimation reduced ROS production in both age groups. TEM images revealed structural differences in cristae membrane area between adults and hatchlings, providing a structural explanation for the observed differences in mitochondrial function. In conclusion, cold acclimation appears protective against oxidative stress from reoxygenation across ages. Despite having a lower anoxia tolerance, hatchlings show lower rates of ROS production compared to adults, which may be due to a lower cristae surface area in the mitochondria. This project was supported by funding from an NSF CAREER grant to Daniel Warren. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.