161 — Mitochondria are physiologically maintained at close to 50 °C

Like yesterday’s, this paper made waves as well, though in a slightly different community. It’s widely known that the process of cellular respiration releases an enourmous amount of heat. In fact, more energy is released in the form of heat than in the form of ATP. This research pulls on that proverbial thread and investigates the temperature of mitochondria (THE POWERHOUSE OF THE CELL) in human embryonic kidney cells and primary skin fibroblasts.

Using a tag that fluoresces in response to temperature, the researchers found that the mitochondria were up to 10ºC warmer when undergoing cellular respiration than when not. When the researchers removed the mitochondrial DNA (effectively stopping cellular respiration) with ethidium bromide (a really nasty compound that I used for years in a genomics lab without fully appreciating how awful it is), the temperature rested at 38ºC, the temperature of the rest of the cellular suspension medium.

The authors are extremely conservative when discussing these findings, despite the impressive rigor with which they conducted them: It’s possible, they explain, that something about their experimental procedure either affected the molecular fluorescence reporter to misrepresent the actual temperature of the mitochondria; or perhaps the temperature differential found in vitro resulted from environmental factors not found in vivo. But the work at least suggests that there is so much more to be learned about the microenvironment of the mitochondrion. If the temperature is really so much higher than we expected human organelles to be, then this might change the way we interpret homeostatic reactions, or the way we develop pharmaceuticals or other therapies.