Not surprisingly this process is sensitive to conditions. Its sensitivity to temperature is mainly in the falling phase, when the original voltage drop is reestablished. This suggests that the potassium channels are more sensitive to temperature and researchers indeed discovered that extreme cold temperatures slows the closing of the potassium channels causing the action potential’s voltage profile to broaden and slowing the nerve cell’s capacity to transmit action potentials.
So how do organisms in extreme cold temperatures compensate? One might think that the potassium channels genes would be adapted, with the proper nucleotide substitutions that would lead to the proper modifications in the potassium channel protein.
But new research, examining octopus species in warm and cold regions, shows that the genetic differences are minor. As the paper explains:
On the basis of conventional natural selection, we hypothesized that the channels’ genes would have evolved mutations to help tune them to their respective environments. Surprisingly, the primary sequences encoded by the two genes were virtually identical, differing at only four positions.
So how do these cold temperature organisms adjust their potassium channels? As the paper concludes, by editing the RNA transcript, the so-called mRNA, of the gene:
the transcribed messenger RNAs are extensively edited, creating functional diversity. One editing site, which recodes an isoleucine to a valine in the channel’s pore, greatly accelerates gating kinetics by destabilizing the open state. This site is extensively edited in both Antarctic and Arctic species, but mostly unedited in tropical species
I just rearranged a sentence in this post. Imagine if I created a computer program to edit the text rather than me editing it manually? That is what these octopus species have, editing machinery to adjust the potassium channels genes automatically, after they are copied from the DNA and before they are translated into proteins. Wow.