Insect chill tolerance is strongly associated with the ability to maintain ion and water homeostasis during cold exposure. Maintenance of K+ balance is particularly important due to its role in setting the cell membrane potential that is involved in many aspects of cellular function and viability. In most insects, K+ balance is maintained through secretion at the Malpighian tubules, which balances reabsorption from the hindgut and passive leak arising from the gut lumen. Here, we used the scanning ion-selective electrode technique (SIET) at benign (23°C) and low (6°C) temperatures to examine K+ flux across the Malpighian tubules and the rectal pads in the hindgut in five Drosophila species that differ in cold tolerance. We found that chill-tolerant species were better at maintaining K+ secretion and suppressing reabsorption during cold exposure. In contrast, chillsusceptible species exhibited large reductions in secretion with no change, oraparadoxical increase, in K+ reabsorption. Usinganassay to measure paracellular leak, we found that chill-susceptible species experience alarge increase in leak during cold exposure, which could explain the apparent increase in K+ reabsorption found in these species. Our data therefore strongly support the hypothesis that coldtolerant Drosophila species are better at maintaining K+ homeostasis through an increased ability to maintain K+ secretion rates and through reduced movement of K+ towards the hemolymph. These adaptations are manifested both at the Malpighian tubule and at the rectal pads in the hindgut, and ensure that cold-tolerant species experience less perturbation of K+ homeostasis during cold stress.

Additional Metadata
Keywords Chill tolerance, Hindgut, Ion regulation, Paracellular leak, SIET
Persistent URL dx.doi.org/10.1242/jeb.168518
Journal Journal of Experimental Biology
Citation
Andersen, M.K. (Mads Kuhlmann), MacMillan, H.A, Donini, A. (Andrew), & Overgaard, J. (Johannes). (2017). Cold tolerance of Drosophila species is tightly linked to the epithelial K+ transport capacity of the Malpighian tubules and rectal pads. Journal of Experimental Biology, 220(22), 4261–4269. doi:10.1242/jeb.168518