Chronic dietary salt stress mitigates hyperkalemia and facilitates chill coma recovery in Drosophila melanogaster

Chill susceptible insects like Drosophila lose the ability to regulate water and ion homeostasis at low temperatures. This loss of hemolymph ion and water balance drives a hyperkalemic state that depolarizes cells, causing cellular injury and death. The ability to maintain ion homeostasis at low temperatures and/or recover ion homeostasis upon rewarming is closely related to insect cold tolerance. We thus hypothesized that changes to organismal ion balance, which can be achieved in Drosophila through dietary salt loading, could alter whole animal cold tolerance phenotypes. We put Drosophila melanogaster in the presence of diets highly enriched in NaCI, ICCI, xylitol (an osmotic control) or sucrose (a dietary supplement known to impact cold tolerance) for 24 h and confirmed that they consumed the novel food. Independently of their osmotic effects, NaCI, KCl, and sucrose supplementation all improved the ability of flies to maintain K+ balance in the cold, which allowed for faster recovery from chill coma after 6 h at 0 degrees C. These supplements, however, also slightly increased the CTmin and had little impact on survival rates following chronic cold stress (24 h at 0 degrees C), suggesting that the effect of diet on cold tolerance depends on the measure of cold tolerance assessed. In contrast to prolonged salt stress, brief feeding (1.5 h) on diets high in salt slowed coma recovery, suggesting that the long-term effects of NaCI and KC1 on chilling tolerance result from phenotypic plasticity, induced in response to a salty diet, rather than simply the presence of the diet in the gut lumen. (C) 2016 Elsevier Ltd. All rights reserved.