Effects of anoxia on ATP, water, ion and pH balance in an insect (Locusta migratoria)

Abstract

When exposed to anoxia, insects rapidly go into a hypometabolic coma from which they can recover when exposed to normoxia again. However, prolonged anoxic bouts eventually lead to death in most insects, although some species are surprisingly tolerant. Anoxia challenges ATP, ion, pH and water homeostasis, but it is not clear how fast and to what degree each of these parameters is disrupted during anoxia, nor how quickly they recover. Further, it has not been investigated which disruptions are the primary source of the tissue damage that ultimately causes death. Here, we show, in the migratory locust (Locusta migratoria), that prolonged anoxic exposures are associated with increased recovery time, decreased survival, rapidly disrupted ATP and pH homeostasis and a slower disruption of ion ([K + ] and [Na + ]) and water balance. Locusts could not fully recover after 4 h of anoxia at 30°C, and at this point hemolymph [K + ] was elevated 5-fold and [Na + ] was decreased 2-fold, muscle [ATP] was decreased to ≤3% of normoxic values, hemolymph pH had dropped 0.8 units from 7.3 to 6.5, and hemolymph water content was halved. These physiological changes are associated with marked tissue damage in vivo and we show that the isolated and combined effects of hyperkalemia, acidosis and anoxia can all cause muscle tissue damage in vitro to equally large degrees. When locusts were returned to normoxia after a moderate (2 h) exposure of anoxia, ATP recovered rapidly (15 min) and this was quickly followed by recovery of ion balance (30 min), while pH recovery took 2-24 h. Recovery of [K + ] and [Na + ] coincided with the animals exiting the comatose state, but recovery to an upright position took ∼90 min and was not related to any of the physiological parameters examined.

Metabolic cost of freeze-thaw and source of CO2 production in the freeze-tolerant cricket Gryllus veletis

“…This loss of coordinated spiracular control at low temperatures, and its re-establishment after rewarming, is consistent with prior observations of both chilled (Lalouette et al, 2011;MacMillan et al, 2012b) and frozen insects (Sinclair et al, 2004). Qualitatively, the pattern of _ V CO 2 during recovery from freezing in crickets bears a striking resemblance to insects recovering from anoxia, where spiracles are likely forced open by the acidification of hemolymph (Lighton and Schilman, 2007;Ravn et al, 2019;Woods and Lane, 2016). A similar acidification of hemolymph following freezing could explain these similarities.…”

“…While insect hemolymph acid-base status is usually well regulated, acid-base homeostasis can be disturbed by temperature and activity, among other factors (Harrison, 2001). For example, under anoxia, the insect hemolymph is acidified (Ravn et al, 2019), mostly likely by the accumulation of lactate (Woods and Lane, 2016), which liberates stored CO 2 as a burst (Lighton and Schilman, 2007) akin to what we observed in crickets at freezing (Fig. 1B).…”

“…1B). Severe acidification of hemolymph is sufficient to damage tissues (Ravn et al, 2019) and may be an overlooked source of freeze injury.…”

Acetylcholinesterase promotes apoptosis in insect neurons

“…The migratory locust has been subject to various studies on pesticide resistance and hypoxia tolerance [ 43 , 89 ]. Various pesticides target AChE in order to disrupt synaptic signalling by acetylcholine, a major transmitter in insect sensory systems and central nervous neuropils.…”

Genome-Wide Association Analysis of Anoxia Tolerance inDrosophila melanogaster

“…An alternative or complementary view of anoxia tolerance, more supported by studies with insects, is that variation in anoxia tolerance is related to differences in abilities to prevent or repair damage despite loss of most ATP. Insects deplete most of their ATP and ion gradients relatively quickly in anoxia, yet survive for many hours or even days (Wegener 1993; Krishnan et al 1997; Campbell et al 2018; Ravn et al 2019). Previous studies have indicated that mechanisms that protect against protein unfolding can be important in anoxia-tolerance, including induction of heat shock proteins (Azad et al 2011; Deng et al 2018), and trehalose (Chen et al 2002), suggesting that genes involved in coping with protein unfolding might be important in intraspecific variation in anoxia tolerance.…”