Can animals that naturally freeze give us some clues for freezing human organs?
Can fish and frogs that naturally freeze give us some clues for freezing human organs?
Barry - Well we've learned along the way that some of these organisms actually have what we call anti-freeze proteins which dictate where the ice starts to form in their bodies. So instead of allowing themselves to freeze all over, they localise the ice that does form into parts of their body that are not going to be injured - the areas under the skin, or the abdominal cavity. They try and avoid freezing inside organs. So again, they're evolutionarily tuned to survive this process.Chris - One point that was made to me in relation to these specialist creatures, like the frogs and toads that can survive being frozen solid, is that if ice does form inside their cells, then the ice forms out of pure water and the solution that's left around the ice crystals is more concentrated so it pulls water into the cell by the process of osmosis, making the cells swell a bit, and then more freezing takes place, and leaves more concentrated water, so the cells swell a bit more, and this ruptures cells. So what they actually do is encourage themselves to freeze really well, really quickly. So in fact, they don't have this process happening to rupture all of their cells. I don't know if you have a perspective on that, Lorna.Lorna - Yes, that's absolutely right. So that's known as osmotic pressure or osmotic stress and in fact, that's how a lot of these organisms develop mechanisms to protect themselves. They can change their solvent composition to either increase the amount of cryoprotectant molecules in the vicinity or reduce it. Humans can do this as well, interestingly. We have membrane proteins called aqua- or glycerolporins and they can control the traffic of water or glycerol molecules across the cell membrane. But obviously we can't do it as effectively as some of these other organisms like the frogs or the fish. But perhaps there is potential there for the future.