Life at -16c: The Impressive Antifreeze Mechanism of Rana Sylvatica

 by Annika Bright

The frog species, Rana sylvatica currently inhabits large expanses of North America and is commonly found in regions above the Artic Circle and throughout the Appalachian Mountains. One of their most remarkable characteristics is their ability to carry out an “antifreeze”-type mechanism, allowing the organisms to survive sub-zero conditions and often even in temperatures of -16 degrees Celsius. 

To determine how this mechanism works, it would be useful to first consider the physiological differences that are evident in freezing temperatures between humans and Rana sylvatica. Notably, once human tissue reaches -0.5 degrees celsius, both the intracellular and extracellular fluid freezes thus, crystallisation occurs and the phospholipid membrane becomes irreversibly damaged. Conversely, within the blood of Rana sylvatica, nucleating proteins encourage water in the blood to freeze initially and so, their intracellular fluid does not freeze. This allows time for the liver to carry out glycogenolysis, hydrolysing glycogen to glucose which is then released into the cells - an antifreeze mechanism. Glucose is pushed into cells, preventing them from becoming dehydrated and shrunken. As a result, once the frog’s environment returns to stable, warm temperatures, their water in the blood thaws and re-enters cells, enabling normal cellular functions to continue. 

So, what could this mean for the future of human organ preservation? Through analysing this mechanism and the structures of antifreeze proteins (AFPs) in other organisms that live in arctic environments, researchers may be able to apply this and develop AFPs that could be used for the long-term preservation of organs.