Most insects have the ability to alter their cold tolerance in response to temporal temperature fluctuations, and recent studies have shown that insect cold tolerance is closely tied to the ability to maintain transmembrane ion gradients that are important for the maintenance of cell membrane potential (Vm). Several studies have therefore suggested a link between preservation of Vm and cellular survival after cold stress, but none has measured Vm in this context. We tested this hypothesis by acclimating locusts (Locusta migratoria) to high (31°C) and low temperature (11°C) for 4 days before exposing them to cold stress (0°C) for up to 48 h and subsequently measuring ion balance, cell survival, muscle Vm, and whole animal performance. Cold stress caused gradual muscle cell death, which coincided with a loss of ion balance and depolarization of muscle Vm. The loss of ion balance and cell polarization were, however, dampened markedly in cold-acclimated locusts such that the development of chill injury was reduced. To further examine the association between cellular injury and Vm we exposed in vitro muscle preparations to cold buffers with low, intermediate, or high [K+]. These experiments revealed that cellular injury during cold exposure occurs when Vm becomes severely depolarized. Interestingly, we found that cellular sensitivity to hypothermic hyperkalaemia was lower in cold-acclimated locusts that were better able to defend Vm whilst exposed to high extracellular [K+]. Together these results demonstrate a mechanism of cold acclimation in locusts that improves survival after cold stress: increased cold tolerance is accomplished by preservation of Vm through maintenance of ion homeostasis and decreased K+ sensitivity.
The authors declare no competing or financial interests.
This study was conceived and designed by M.K.A. and J.O. Experiments were carried out by M.K.A and R.F. M.K.A. and H.A.M. analysed the data. M.K.A. and J.O. wrote first draft, and all authors contributed to and approved the final version.
This research was funded by a grant from Det Frie Forskningsråd | Natur og Univers (to J.O.) and a grant from Naturvidenskab og Teknologi, Aarhus Universitet (to M.K.A.).
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.150813.supplemental
- Received October 3, 2016.
- Accepted November 18, 2016.
- © 2017. Published by The Company of Biologists Ltd