Oxygen consumption by isolated mitochondria: Software for planning and interpreting experiments

A computer program for teaching is described which stimulates oxygen consumption by isolated mitochondria. The effects of different compounds (substrates, inhibitors, uncouplers) may be tested. Results from evaluation with 166 undergraduate and 11 postgraduate students are presented.     

Oxygen consumption in Tardigrada from Spitsbergen

Summary Oxygen consumption was measured in seven species of Tardigrada (Doryphoribius smreczynskii, Diphascon spitzbergensis, Macrobiotus islandicus, M. echinogenitus, M. harmswothi, M. spectabilis and M. dispar) from the Spitzbergen tundar. The metabolic rate was measured at 2°, 6° and 10°C. At 6°C it ranged from 0.055 (D. smreczynskii) to 0.101 mm³·10^-3/g·10^-6h (M. harmswothi). In D. smreczynskii the phenomenon of relative thermal independence was observed at a temperature range of 2°–6°C. The dependence of oxygen consumption (R in mm³·10^-3·individ^-1·h^-1) on body weight (W in g·10^-6) for the latter species at 2°C was R=0.088·W^0.82.     

Predicting small endotherm body temperatures from scalp temperatures

We used 2-d to 3-d-old mallard ducklings (Anas platyrhynchos) to test whether remote thermographic measurement of scalp temperature could be used to estimate core (cloacal) temperature from a distance. The scalp was exposed by trimming down from an area of ⩽1 cm², and surface temperature measured to ±0.12 °C with a radiometric thermal imager. For wind speeds of up to 2.5 m/s, we found cloacal temperature could be estimated to within 1 °C by using a regression model incorporating only scalp temperature and ambient temperature. The inexpensive method of dyeing the scalp black and painting it with temperature-sensitive cholesteric liquid crystal paint is more difficult and provides less accuracy, but appears to be a useful means for monitoring change in body temperature. These methods allow body temperatures of small or young endotherms to be monitored from distances of up to several meters without surgery or encumbering wires, minimizing stress that may alter behavior patterns and physiological parameters.     

Ethanol consumption and liver mitochondria function

The mitochondrion is the subcellular organelle affected earliest during the development of alcoholic liver disease. As a result of chronic ethanol consumption mitochondrial protein synthesis is decreased significantly due to a depression in the functioning of the mitochondrial ribosome. This causes a significant decrease in the concentrations of the thirteen mitochondria gene products, all of which are components of the oxidative phosphorylation system. Consequently, there is a depression in the rate at which ATP is synthesized in hepatic mitochondria. In addition to this loss in function, hepatic mitochondria either acutely or chronically exposed to ethanol generate increased levels of reactive oxygen species (ROS). This elevation in ROS has been demonstrated in both isolated mitochondria and hepatocytes. The increase in mitochondrial ROS production accompanying acute ethanol exposure is due to mitochondrial associated reoxidation of NADH produced during ethanol and acetaldehyde metabolism. The elevation in ROS generation observed in mitochondria from chronic ethanol consumers is likely due to decreases in mitochondrial-derived electron transport components, which in turn results in higher levels of the semiquinone forms of flavin mononucleotide and ubiquinone. Both these semiquinones readily donate electrons to molecular oxygen to form superoxide.     

Simulated heat waves reduce cognitive and motor performance of an endotherm

1. Heat waves cause mass mortality of animals, including humans, across the globe annually, which has drawn new attention to how animals cope with high air temperatures. Recent field research has explored behavioral responses to high air temperatures, which can influence reproductive success and mortality.
2. Less well studied are the effects of high air temperatures on cognition, which may underlie behavioral changes. Specifically, it is poorly known if cognitive declines occur at high temperatures, and if cognitive and motor components of behavior are similarly affected.
3. We tested how well zebra finches (Taeniopygia guttata castanotis), a model for cognition research, performed two learned foraging tasks (color association and detour‐reaching) at mild (22°C) and high (43 and 44°C) air temperatures that occur naturally in their range. We habituated birds to the trial conditions and temperatures on days preceding the test trials and at the trial temperature for 30 min immediately prior to each test trial. Trials lasted less than 10 min. At high air temperatures, zebra finches exhibited heat dissipation behaviors during most tasks, suggesting thermoregulatory challenge.
4. Cognitive performance declined at high air temperatures in two of three measures: Color association was unaffected, but birds missed more food rewards, and did more unproductive behaviors. Motor performance declined at high temperatures on the color association task, including longer times to complete the task, move between food rewards, and process individual seeds. Performance declines varied among components of behavior and among individuals.
5. We combined our behavioral data with existing climate data and predicted that in the austral summer of 2018–2019, zebra finches experienced air temperatures that caused cognitive and motor declines in our captive birds in 34% and 45% of their Australian range, respectively.
6. This study provides novel experimental evidence that high air temperatures cause cognitive and motor performance decline in birds. Further, our results provide insights to how those declines might affect bird ecology and evolution. First, differences in declines among behavioral components may allow identification of behaviors that are most susceptible to decline in the wild. Second, variation in performance declines and heat dissipation behaviors among individuals suggests variability in heat tolerance, which could lead to differential fitness in the wild. Last, these results suggest that high air temperatures cause cognitive declines in the wild and that understanding cognition could help refine predictive models of population persistence.

     

A warmer environment can reduce sociability in an ectotherm

The costs and benefits of being social vary with environmental conditions, so individuals must weigh the balance between these trade-offs in response to changes in the environment. Temperature is a salient environmental factor that may play a key role in altering the costs and benefits of sociality through its effects on food availability, predator abundance, and other ecological parameters. In ectotherms, changes in temperature also have direct effects on physiological traits linked to social behaviour, such as metabolic rate and locomotor performance. In light of climate change, it is therefore important to understand the potential effects of temperature on sociality. Here, we took the advantage of a ‘natural experiment’ of threespine sticklebacks from contrasting thermal environments in Iceland: geothermally warmed water bodies (warm habitats) and adjacent ambient-temperature water bodies (cold habitats) that were either linked (sympatric) or physically distinct (allopatric). We first measured the sociability of wild-caught adult fish from warm and cold habitats after acclimation to a low and a high temperature. At both acclimation temperatures, fish from the allopatric warm habitat were less social than those from the allopatric cold habitat, whereas fish from sympatric warm and cold habitats showed no differences in sociability. To determine whether differences in sociability between thermal habitats in the allopatric population were heritable, we used a common garden breeding design where individuals from the warm and the cold habitat were reared at a low or high temperature for two generations. We found that sociability was indeed heritable but also influenced by rearing temperature, suggesting that thermal conditions during early life can play an important role in influencing social behaviour in adulthood. By providing the first evidence for a causal effect of rearing temperature on social behaviour, our study provides novel insights into how a warming world may influence sociality in animal populations.     

Oxygen consumption and production by tropical ascidians symbiotic with Prochloron

• 1.1. Oxygen consumption and production rates were measured in two species of colonial ascidians that contained the algal symbiont, Prochloron.
• 2.2. Despite differences in size and habitats, the colonies showed similar rates of oxygen consumption and production.
• 3.3. Oxygen production by the colonies was light dependent.
• 4.4. Based on the data presented, the symbiosis is similar to other algal-invertebrate symbioses in producing more oxygen than is consumed when illuminated.

     

Oxygen consumption by ruminal microorganisms: protozoal and bacterial contributions

The relative contributions to O2 consumption made by the protozoal and bacterial populations present within the rumen were determined by using an open-type oxygen electrode system. Measurements indicated that two separate microbial populations contributed approximately equally to ruminal O2 consumption over the O2 concentration range experienced in situ (0.25 to 1.0 microM). The populations were observed to consume O2 under liquid-phase O2 concentrations of up to 7 microM, above which point rapid inactivation of O2 utilization was observed. Km values for the mixed population of bacteria and protozoa were 0.36 +/- 0.17 and 3.2 +/- 0.4 microM at concentrations of less than 1.6 and greater than 1.6 microM, respectively. O2 affinity values obtained for both the protozoal and bacterial populations were similar. O2 affinities of the isolated entodiniomorphid ciliates Polyplastron multivesiculatum and Eudiplodinium maggii showed O2 inhibition thresholds of 10 and 5, respectively, and apparent half-saturation constants (Km values) of 1.7 and 5.2 microM O2, respectively. Corresponding Vmax values were 7.8 microM O2 per min per 10(5) organisms for P. multivesiculatum and 3.6 microM O2 per min per 10(5) organisms for E. maggii. Mass spectroscopic analysis detected average rates of H2 production of 12.0 and 3.7 microM H2 per min per 10(5) organisms for P. multivesiculatum and E. maggii, respectively. Trace levels of dissolved O2 (less than 0.25 microM) stimulated the H2 production rate of E. maggii eightfold but inhibited that of P. multivesiculatum by 18%.     

Oxygen consumption by tumor cells during membrane vesicle shedding

The incubation of mastocytoma P815 cells at low temperature (0 degrees C/1-2 hr), with a subsequent shift to greater than or equal to 20 degrees C results in the formation and shedding of membrane vesicles from the tumor cell surfaces. This process, when occurring at physiologic temperature (37 degrees C), mimics the morphological and membrane permeability changes occurring during T-lymphocyte mediated cytolysis of tumor cells. The latter is an oxygen dependent event, but it is not known whether this requirement is at the effector T cell or at the tumor cell level. The present study investigated the oxygen consumption rates of mastocytoma P815 cells induced to shed membrane vesicles by a temperature shift (0 degrees C/1-2 hrs----greater than or equal to 20 degrees C). Results showed that cells undergoing the membrane vesicle shedding process had significantly higher oxygen requirements than control non-shedding cells. Inhibition of the shedding process with deuterium oxide and hexylene glycol, reduced the oxygen consumption rates of low temperature treated cells to the level of control cells. The oxygen consumption rates of the latter were unaffected by these microtubule stabilizing agents. These data indicate that the oxygen required for immune T-cell mediated lysis of tumor cells may be at the target tumor cell level.     

Oxygen consumption by rat oocytes and cumulus cells during induced atresia

Oxygen consumption was measured in denuded oocytes and oocyte-cumulus complexes isolated from atretic rat follicles. Adult cyclic rats or immature PMSG-treated rats were used, and follicular atresia was induced by hypophysectomy on the morning of pro-oestrus or by repeated pentobarbitone injections beginning on the day of pro-oestrus. The later stages of atresia were accompanied by meiosis-like changes in the oocytes. Oxygen consumption by oocytes that had resumed meiosis (germinal vesicle breakdown, GVB) was higher than in oocytes with an intact germinal vesicle, a change similar to that observed in oocytes maturing in healthy follicles. This may indicate that the meiotic process in the atretic follicles is similar to that in normal ones. Oxygen consumption by the cumulus cells was not altered during pentobarbitone-induced atresia. Hypophysectomy led to a rapid and marked increase in cumulus oxygen consumption in cyclic rats but there was no change in PMSG-treated young animals. Since both pentobarbitone-treatment and hypophysectomy result in follicular atresia, but changes in cumulus respiration occurred only in hypophysectomized adult rats, it is concluded that an increase in cumulus respiration is not inherent to the atretic process.     

Oxygen consumption by ruminal microorganisms: protozoal and bacterial contributions.

The relative contributions to O2 consumption made by the protozoal and bacterial populations present within the rumen were determined by using an open-type oxygen electrode system. Measurements indicated that two separate microbial populations contributed approximately equally to ruminal O2 consumption over the O2 concentration range experienced in situ (0.25 to 1.0 microM). The populations were observed to consume O2 under liquid-phase O2 concentrations of up to 7 microM, above which point rapid inactivation of O2 utilization was observed. Km values for the mixed population of bacteria and protozoa were 0.36 +/- 0.17 and 3.2 +/- 0.4 microM at concentrations of less than 1.6 and greater than 1.6 microM, respectively. O2 affinity values obtained for both the protozoal and bacterial populations were similar. O2 affinities of the isolated entodiniomorphid ciliates Polyplastron multivesiculatum and Eudiplodinium maggii showed O2 inhibition thresholds of 10 and 5, respectively, and apparent half-saturation constants (Km values) of 1.7 and 5.2 microM O2, respectively. Corresponding Vmax values were 7.8 microM O2 per min per 10(5) organisms for P. multivesiculatum and 3.6 microM O2 per min per 10(5) organisms for E. maggii. Mass spectroscopic analysis detected average rates of H2 production of 12.0 and 3.7 microM H2 per min per 10(5) organisms for P. multivesiculatum and E. maggii, respectively. Trace levels of dissolved O2 (less than 0.25 microM) stimulated the H2 production rate of E. maggii eightfold but inhibited that of P. multivesiculatum by 18%.