Regulation of pyruvate dehydrogenase in the common killifish, Fundulus heteroclitus , during hypoxia exposure.

Self Cite

114

Human activities are increasing both the frequency of hypoxic episodes and the mean temperature of aquatic ecosystems, but few studies have considered the possibility that acclimation to one of these stressors could improve the ability to cope with the other stressor. Here, we used Atlantic killifish, Fundulus heteroclitus, to test this hypothesis. Hypoxia tolerance was measured as time to loss of equilibrium in hypoxia (LOE hyp ) at 0.4 kPa oxygen. Time to LOE hyp declined from 73.3±6.9 min at 15°C to 2.6±3.8 min at 23°C, and at 30°C no fish could withstand this level of hypoxia. Prior acclimation to warm temperatures significantly increased time to LOE hyp . Hypoxia tolerance of the southern subspecies of killifish, F. heteroclitus heteroclitus, was greater than that of the northern subspecies, F. heteroclitus macrolepidotus, measured both as critical oxygen tension (P crit ) and as time to LOE hyp . Warm acclimation offset the negative effects of temperature on time to LOE hyp to a similar extent in the two subspecies. Warm acclimation increased total lamellar surface area of the gill in both subspecies as a result of regression of an interlamellar cell mass (ILCM). However, differences in total lamellar surface area could not explain differences in time to LOE hyp between the subspecies, suggesting that the lower time to LOE hyp of northern fish is related to their higher routine metabolic rate. These data suggest that thermal plasticity in gill morphology can improve the capacity of this species to tolerate hypoxia, and shows how existing plasticity may help organisms to cope with the complex interacting stressors that they will encounter with increasing frequency as our climate changes.

Section: Introductionmentioning

confidence: 99%

Warm acclimation improves hypoxia tolerance in Fundulus heteroclitus

McBryan

Healy

Haakons

et al. 2016

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114

“…Killifish are very tolerant of hypoxia (Richards et al, 2008;Borowiec et al, 2015) and must cope with both seasonal and daily fluctuations in dissolved oxygen in their native estuarine habitat (Tyler et al, 2009). Hypoxia acclimation alters many physiological traits involved in O 2 transport and utilization in this species, including the activity of several oxidative and gluconeogenic enzymes in the liver (Borowiec et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Mitochondrial physiology and reactive oxygen species production are altered by hypoxia acclimation in killifish (Fundulus heteroclitus)

Mahalingam

Borowiec

et al. 2016

Many fish encounter hypoxia in their native environment, but the role of mitochondrial physiology in hypoxia acclimation and hypoxia tolerance is poorly understood. We investigated the effects of hypoxia acclimation on mitochondrial respiration, O 2 kinetics, emission of reactive oxygen species (ROS), and antioxidant capacity in the estuarine killifish (Fundulus heteroclitus). Killifish were acclimated to normoxia, constant hypoxia (5 kPa O 2 ) or intermittent diel cycles of nocturnal hypoxia (12 h:12 h normoxia: hypoxia) for 28-33 days and mitochondria were isolated from liver. Neither pattern of hypoxia acclimation affected the respiratory capacities for oxidative phosphorylation or electron transport, leak respiration, coupling control or phosphorylation efficiency. Hypoxia acclimation also had no effect on mitochondrial O 2 kinetics, but P 50 (the O 2 tension at which hypoxia inhibits respiration by 50%) was lower in the leak state than during maximal respiration, and killifish mitochondria endured anoxia-reoxygenation without any impact on mitochondrial respiration. However, both patterns of hypoxia acclimation reduced the rate of ROS emission from mitochondria when compared at a common O 2 tension. Hypoxia acclimation also increased the levels of protein carbonyls and the activities of superoxide dismutase and catalase in liver tissue (the latter only occurred in constant hypoxia). Our results suggest that hypoxia acclimation is associated with changes in mitochondrial physiology that decrease ROS production and may help improve hypoxia tolerance.

“…lactate dehydrogenase), or by reducing carbohydrate flux into the tricarboxylic acid cycle and decreasing aerobic enzyme activity (e.g. cytochrome c oxidase, citrate synthase) (van den Thillart et al, 1980(van den Thillart et al, , 1994Almeida-Val et al, 1995;Martínez et al, 2006;Richards et al, 2008). In addition to mechanisms that help maintain ATP supply, some tolerant organisms can also reduce ATP demands through active depression of resting metabolic rate (van Waversveld et al, 1989;van Ginneken et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

Distinct physiological strategies are used to cope with constant hypoxia and intermittent hypoxia in killifish (Fundulus heteroclitus)

Borowiec

Darcy

Gillette

et al. 2015

Many fish encounter hypoxia on a daily cycle, but the physiological effects of intermittent hypoxia are poorly understood. We investigated whether acclimation to constant (sustained) hypoxia or to intermittent diel cycles of nocturnal hypoxia (12 h normoxia:12 h hypoxia) had distinct effects on hypoxia tolerance or on several determinants of O 2 transport and O 2 utilization in estuarine killifish. Adult killifish were acclimated to normoxia, constant hypoxia, or intermittent hypoxia for 7 or 28 days in brackish water (4 ppt). Acclimation to both hypoxia patterns led to comparable reductions in critical O 2 tension and resting O 2 consumption rate, but only constant hypoxia reduced the O 2 tension at loss of equilibrium. Constant (but not intermittent) hypoxia decreased filament length and the proportion of seawatertype mitochondrion-rich cells in the gills (which may reduce ion loss and the associated costs of active ion uptake), increased blood haemoglobin content, and reduced the abundance of oxidative fibres in the swimming muscle. In contrast, only intermittent hypoxia augmented the oxidative and gluconeogenic enzyme activities in the liver and increased the capillarity of glycolytic muscle, each of which should facilitate recovery between hypoxia bouts. Neither exposure pattern affected muscle myoglobin content or the activities of metabolic enzymes in the brain or heart, but intermittent hypoxia increased brain mass. We conclude that the pattern of hypoxia exposure has an important influence on the mechanisms of acclimation, and that the optimal strategies used to cope with intermittent hypoxia may be distinct from those for coping with constant hypoxia.