Figure 3.

A revised model of cause-and-effect relationships between cold exposure and chilling injury phenotypes in insects. Exposure to stressful cold directly depolarizes cell membranes, and this effect is exacerbated by both a systemic (haemolymph; impacting muscles) and local (spreading depolarization; impacting the central nervous system) loss of K⁺ balance. This causes cell membrane depolarization that drives a catastrophic increase in cytosolic [Ca⁺] in muscle cells which activates executioner caspases and the resulting apoptotic cell death likely contributes to injury at the organismal level. Based on the findings of the present study, however, it is likely that other cell-death pathways (e.g. necrosis) or deleterious (and potentially Ca²⁺-overload-independent) mechanisms in the neuromuscular system are activated by membrane depolarization and cause the majority of chilling injury. (Online version in colour.)