55.4 Thursday, Jan. 5 RNA editing underlies temperature adaptation in K+ channels from polar octopuses GARRETT, Sandra/C*; ROSENTHAL, Joshua/JC; University of Puerto Rico, Institute of Neurobiology; University of Puerto Rico, Institute of Neurobiology email@example.com
Early studies with squid giant axons showed that K+ channels, and the action potential phases they underlie, are especially temperature sensitive suggesting that in polar cephalopods they could be targets for adaptation. To look for evidence of cold adaptation, we compared orthologs of the squid delayed rectifier K+ channel from a tropical and an Antarctic octopus. The two genes encoded channels that differed at only 4 positions, and when the channels were expressed in a heterologous system they had nearly identical electrophysiological properties. Since we found no evidence of gene level adaptation in the Antarctic channel, we next considered A-to-I RNA editing, which is known to generate substantial diversity in squid K+ channels. Twelve RNA editing sites were identified in the octopus channels, four of which were edited differently between the two species. Among these, the site I321V appeared cold adaptive: it was almost completely edited in the Antarctic channel but mostly unedited in the tropical channel, and it dramatically accelerated channel closing. Models based on single channel and macroscopic currents suggested that I321V doubled the rate of the open state to closed state transition, thereby speeding closing kinetics with little effect on open probability, or opening kinetics. If I321V were truly used for cold adaptation, then we would expect the level of editing at this site to correlate with ambient temperature for other octopus species. We measured I321V editing in six additional species and found high levels in Arctic species, low levels in tropical species, and intermediate levels in temperate species. In conclusion, octopus K+ channels do have cold adaptive structural changes, but these changes are coded at the level of RNA processing, not in the gene.