Do ion‐motive pumps contribute to cold‐acclimation in Drosophila ?

At low temperatures Drosophila , like most insects, lose the ability to regulate ion and water flux across the gut epithelia, which leads to a lethal accumulation of K + in the hemolymph. Cold‐acclimation can mitigate or entirely prevent these ion imbalances, but the physiological mechanisms that facilitate these plastic changes are not understood. This study assessed the activity of Na + /K + ‐ATPase (NKA), and V‐Type H + ATPase (VA) in the primary ionoregulatory tissues of Drosophila (the gut and the Malpighian tubules) to test whether modulation of their activity is a potential mechanism of cold‐acclimation. Upon adult emergence, D. melanogaster females were subjected to seven days at 25°C (warm acclimation) or 10°C (cold acclimation). Cold‐acclimation reduced the critical thermal minimum (CT min ), sped up recovery from chill coma, and improved survival following prolonged cold stress, suggesting that cold acclimation may be mitigating ion imbalance resulting from cold in our flies. We then quantified both NKA and VA activity in the hindgut, midgut, and the Malpighian tubules of warm‐ and cold‐acclimated flies. Using Ramsay assays, Malpighian tubule fluid secretion rates were compared for warm and cold acclimated flies, and the Na + and K + concentrations of secreted fluid were measured with ion‐selective microelectrodes. The scanning ion‐selective electrode technique was used to measure the Na + and K + flux across the midgut and hindgut epithelia of warm and cold acclimated flies. The effects of cold acclimation on ionomotive pump activity, Malpighian tubule function and ion fluxes across the Drosophila gut are presented. This study sheds light on the underlying physiological mechanisms that facilitate changes that mitigate the loss of ion balance upon a cold stress. Support or Funding Information NSERC Discovery Grant to Andrew DoniniBanting Postdoctoral Fellowship to Heath MacMillan