Muscle membrane potential and insect chill coma

Abstract

Chill susceptible insects enter a reversible paralytic state, termed chill coma, at mild low temperatures. Chill coma is caused by neuromuscular impairment, allegedly triggered by cold-induced depolarization of muscle resting membrane potential (Vm). We used five Drosophila species that vary in cold tolerance (chill coma temperature spanning approx. 11°C) and repeatedly measured muscle Vm during a downward temperature ramp (20 to -3°C). Cold tolerant species were able to defend their Vm down to lower temperatures. An ability not explained by species specific differences in initial Vm at 20°C, but by cold tolerant drosophilids defending Vm across a broad range of temperatures. We found support for a previously suggested “critical threshold” of Vm, related to chill coma, in three of the five species, interestingly, the cold tolerant Drosophila species may enter coma due to processes unrelated to muscle depolarization as their Vm was not significantly depolarized at their chill coma temperatures.