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Excited to read this new addition to the literature on insect ion balance and cold tolerance by @JackieLebz @_FlourFly and @brentjsinclair! I'll add my thoughts to this thread. https://www.sciencedirect.com/science/article/pii/S1095643320300519#f0045
1) Cold adapted and acclimated insects are more cold tolerant and often have lower Na+ gradients. This has been seen in crickets, but also among fly species that come from different climates and with cold acclimated flies. https://www.sciencedirect.com/science/article/pii/S0022191015000773?via%3Dihub https://jeb.biologists.org/content/219/16/2504
9) Science is humbling and these kinds of results are the best!
10) Central to these unexpected effects is the complexity of interactions in biochemistry and physiology, especially when dealing with multiple organs interacting over different timescales.
3) The approach is elegant, and worked beautifully to alter Na+ gradients, allowing for a clear test of their hypothesis. This approach is an example of a strong test of mechanistic hypotheses, and the kind of thing I have been advocating for more of: https://jeb.biologists.org/content/222/4/jeb191593.abstract
4) There was no effect on the CTmin. This is exactly what many in our field would predict given the strong advancements in our understanding of neuronal spreading depolarization: https://www.sciencedirect.com/science/article/pii/S1095643318302976?via%3Dihub
6) @hedavis_msc’s first PhD chapter will make that even more abundantly clear soon!
7) Although a high [Na+] diet reduces the Na+ gradient and reduces CCRT, it also causes greater cold mortality through worse disruption of K+ and water balance. The extent of K+ disruption seems quite central to cold-induced injury, which fits with the current model.
8) This unexpected effect of the diet doesn’t surprise me at all. @gili94 thought a high K+ diet would make fruit flies less cold tolerant by making hyperkalemia worse. Nope – it makes them more cold tolerant. Undergrads in my lab are now close to understanding why.
2) Here, the authors suggest that directly manipulating these gradients might be a way to alter cold tolerance. Neat idea!
11) For example, cold acclimated insects can decouple hyperkalemia from cell death. The Overgaard lab has good ideas for how that works in muscles relation to Ca2+ overload, but it is not yet completely understood: https://www.pnas.org/content/115/41/E9737. @nickteetsUK probably isn't surprised :)
