life on ice

: "New Scientist May 2,1998: 24-28 'Life on Ice' Various quoted snippets: 'Wood frogs, it turns out, only look frozen solid. In reality, the water in between their cells freezes, but not the water within them. To achieve this semi-frozen state, the frogs adopt two main strategies. First their blood contains ice nucleating proteins - molecules that actually encourage ice to grow by mimicking its crystal lattice. 'If you could fly over a nucleating protein in a miniature airplane,' story says, 'its surface would look like ice.' With so many nucleators in the blood, no one crystal ever gets big enough to damage tissue. Glucose is the second trick. Just as the extremities begin to get icy, the frog's liver starts churning out glucose, which circulates round its body. 'The frogs start out with the same amount of glucose we have,' says Storey, 'then go right to being diabetic.' Glucose in the cells has the same effect as antifreeze in a car radiator - it drives the freezing temperature down. Consequently, the cells' syrupy insides stay liquid even while the remaining 65 per cent of the water in the frog has turned to ice. Just as frogs use glucose, Arctic brine shrimp and many cold-tolerant insects use a sugar called trehalose, which forms a syrup as thick as stretchy toffee, is even better at lowering freezing points and stopping dehydration than glycerol or glucose. But just like glucose, it crosses membranes slowly. How then to get it into the cells so that it can work its magic? The answer, Beattie says, is to take advantage of the cold-induced leaky membranes. She and her UCSD colleague Alberto Hayek slowly cooled human insulin-producing cells in a trehalose solution, and just as the lipid membrane started to congeal at around 5 C, the trehalose leaked in. Then Beattie plunged the cells into liquid nitrogen to rapidly finish the freezing process. Given the progress that's been made, is there any hope of freezing and reviving a whole human? Barring some unforeseen breakthrough, such cryogenic time capsules will very likely remain impossible, according to most experts. Scaling up techniques that work on bits of humans won't work for the whole thing. high levels of sugar trigger diabetic shock, for instance, and glycerol would be toxic when you thawed out and started to metabolise it. And even if we could handle such chemicals, getting them inside all the cells in the body would be problematic. That's not to say that people like Storey don't wish they could freeze humans. 'If by magic I could fill you with high levels of sugar and put nucleating proteins in your blood,' says Storey, 'then I could freeze you.' unfortunately, the operative word, he says, is magic'.' Suggestion by poster: Try sorbitol instead. This sugar penetrates cell membranes much better than glucose or trehalose, and is nontoxic."