Kinetics of oxygen and carbon monoxide binding to the hemoglobins of the water snakes Liophis miliaris and Helicops modestus

• 1.1. Liophis miliaris and Helicops modestus are water snakes having different respiratory adaptiations to their specific habitats. L. miliaris is more active and spends more time on land than H. modestus. Knowledge of the equilibrium and kinetics of ligand binding to their hemoglobins leads to better understanding of molecular aspects of this adaptation.
• 2.2. Both snakes contain several hemoglobin types in their blood. Studies on the kinetics of oxygen dissociation and carbon monoxide combination with these hemoglobins were performed by stopped-flow and flash-photolysis experiments at various pH values, both in the presence and absence of adenosine triphosphate.
• 3.3. The oxygen dissociation kinetics of L. miliaris hemoglobins show a strong pH dependence and cooperative interactions between chains are indicated by autocatalytic time-courses at pH 7.0. In contrast, H. moledstus hemoglobins show nearly pH independent rate constants for oxygen dissociation and cooperative interactions between chains were not apparent. The hemoglobins of H. modestus show increased pH dependence in the presence of adenosine triphosphate.
• 4.4. The carbon monoxide combination kinetics differ for the hemoglobins of L. miliaris and H. modestus in general agreement with the differences found in the kinetics and equilibria of oxygen binding. Both the kinetic and steady-state difference between these hemoglobins may be advantageous in light of the behavioral differences of these two water snakes.

     

The pattern and influential factors of aquatic pharyngeal movements of Trionyx sinensis

• 1.1. The pharyngeal movements of Trionyx sinensis during submersion where recorded with physiological instruments.
• 2.2. Anoxia or hypercapnia caused a marked increase in breathing rate of tested turtles during voluntary diving, and in anoxia there was a significant increase in the frequency of aquatic pharyngeal movements while hypercapnia had a slight or no effect on the frequency of these movements.
• 3.3. During voluntary diving when turtles could easily extend their heads out of water to breathe air, the frequency of rhythmic pharyngeal movements was lower; but during forced submersion, the frequency was higher and the movements were continuous.
• 4.4. The frequency increased more rapidly and greatly when turtles were in forced submersion than when they dived freely and could easily surface to breathe in N₂.
• 5.5. The frequency of pharyngeal movements of T. sinensis during diving in an aquarium with water depth of 30 or 45 cm was markedly higher than that at a water depth of 15 cm. Disturbing stimuli also influenced the aquatic rhythmic pharyngeal movements of T. sinensis.

     

Relationship between heart rate and oxygen consumption in the intertidal limpets Patella granularis and Siphonaria oculus

• 1.1. Aerial heart rate and _O2 linearly correlated for Patella granularis and Siphonaria oculus when these parameters were varied by changing ambient temperature. This relationship for P. granularis was significantly transposed above that for S. oculus.
• 2.2. While prolonged aerial exposure (+24hr) lowered the curve for heart rate against _O2 for P. granularis below that determined over short-term exposure (< 12 hr), it had no significant effect on this relationship for S. oculus.
• 3.3. The correlations of heart rate and oxygen consumption are discussed in terms of functioning of the circulatory system and the predictability of one parameter from the other.

     

Metabolic responses of the mussels Perna viridis and Perna indica to declining oxygen tension at different salinities

• 1.1. Oxygen uptake and ammonia loss were monitored during responses to reductions of both salinity and oxygen tension (PO₂) in the marine mussels Perna viridis and Perna indica from southern India.
• 2.2. The proportional contribution of protein to total catabolic substrates under natural environmental conditions was as much as 96% in P. viridis, relative to only 19% in P. indica.
• 3.3. Normoxic oxygen consumption remained statistically unchanged in P. viridis conditioned to salinities between 32 and 15‰, with no obvious signs of distress. Although equally unaffected at salinities between 32 and 20‰, P. indica showed significantly reduced oxygen uptake following transfer from 32 to 15‰, and had died within the next 7 days.
• 4.4. At salinities greater than 20‰, P. viridis was better able than P. indica to regulate oxygen consumption independent of PO₂.
• 5.5. P. indica showed a compensatory increase in oxyregulatory capacity at 15‰. This exceeded unstressed abilities, helping to maintain albeit reduced oxygen uptake throughout wider ranges of PO₂.
• 6.6. Different responses recorded in each of these tropical and often intertidal species were in accordance with their natural distributions. Nevertheless, the oxyregulatory capacity in both species was higher than in bivalves from temperate and/or subtidally restricted habitats.

     

Ventilation and blood acid-base balance of the crayfish as functions of water oxygenation (40–1500 Torr)

• 1.1. The specific ventilation, that is, the volume of water breathed to obtain a unit quantity of oxygen, was studied in 21 crayfish Astacus leptodactylus at partial pressures of O₂. PI_o2. between 40 and 1500 Torr.
• 2.2. The acid-base balance of the prebranchial hemolymph was studied in 17 other specimens between 43 and 575 Torr; the hemolymph pH was also measured at 1450 Torr in 11 other animals. Temperature of the water was controlled at 13°C, and its acid-base balance at a CO₂ pressure of 0.8 Torr and a pH of 8.40. The water was regularly renewed to avoid changes in ionic concentration.
• 3.3. The specific ventilation varied between 301.mmol⁻¹ in hypoxia (40 Torr) and 1 l·mmol⁻¹ in hyperoxia (1500 Torr). The actual ventilatory flow varied in about the same ratio since in this range of oxygenation the oxygen consumption is stable.
• 4.4. The values of pH and P_co2 of prebranchial hemolymph were respectively 7.99 and 1.3 Torr in hypoxia (PI_o2 = 43 Torr), 7.86 and 1.9 Torr in normoxia, and 7.73 and 4.7 Torr in hyperoxia (PI_o2 = 575 Torr). At PI_o2, = 1450 Torr. hemolymph pH was 7.60.
• 5.5. This study points up the tolerance of the crayfish to wide ranges of oxygen concentrations, the oxygen dependency of the ventilation which varied by a factor of 30 between 40 and 1500 Torr P_o2, and the oxygen dependency of the hemolymph acid-base balance, since pH varied 0.4 unit between hypoxia and hyperoxia.

     

The dependence of oxygen consumption of the common whelk (Buccinum undatum) on hypoxia,salinity and air exposure

• 1.1. Oxygen consumption of low salinity (20‰) acclimated whelks decreases markedly upon acute exposure to hypoxia (P_WO₂ = 35 Torr), but almost regenerates its original level within 48 hr exposure to the hypoxic condition.
• 2.2. This ability to regain the original level of oxygen consumption is not seen in high salinity (35‰) acclimated whelks.
• 3.3. Oxygen consumption in air at 10°C is more than twice the rate shown by low salinity acclimated whelks in normoxic water (P_WO₂ = 150 Torr).
• 4.4. Q₁₀ for oxygen consumption in air is about 1.0 in the temperature range 10–20°C.

     

The influence of aerial exposure on gas exchange and cardiac activity in the shore crab,Carcinus maenas (L.)

• 1.1. The cardiovascular physiology of adult Carcinus maenas (L.) emerging into air has been investigated at three different air temperatures.
• 2.2. Transition from seawater to air or vice versa triggered transient increases in cardiac and locomotor activity.
• 3.3. However, crabs became inactive 5–10 min after emerging from seawater (15°C) into air at the same temperature (15°C) or at lower temperatures (12–13°C) and heart rate fell.
• 4.4. At higher air temperatures (18–20°C) heart rate rose but to a lesser extent than predicted from aquatic Q₁₀ heart-rate values.
• 5.5. Crabs were again quiescent in aerial conditions.
• 6.6. Mean arterial oxygen tension (Pa_o2) was ~ 74 mmHg in submerged crabs but fell to ~ 38 mmHg in air while mean arterial carbon dioxide tension (Pa_o2) increased from 1 to 4 mmHg resulting in respiratory acidosis.
• 7.7. A model of gill function is proposed to explain the development of internal hypoxia in air.
• 8.8. The results are discussed in relation to the distribution of adult and juvenile C. maenas in situ.

     

The oxygen consumption rates of three gastrotrichs

• 1.1. The oxygen consumption rates for three sympatric species of marine gastrotrichs (anatomically similar, except that one contains hemoglobin) were measured with a Cartesian diver microrespirometer.
• 2.2. The rates for the two species without hemoglobin, Turbanella ocellata and Dolichodasys carolinensis, were 307.2 μl O₂ g⁻¹ hr⁻¹ and 108.0 μl O₂ g⁻¹ hr⁻¹, respectively, while the rate for the hemoglobin-containing species, Neodasys, was 208.9 μl O₂ g⁻¹ hr⁻¹.
• 3.3. The possession of hemoglobin by Neodasys (14% by volume) cannot be explained by an unusually high demand for oxygen.
• 4.4. Instead, the hemoglobin may be useful as an oxygen store providing continued aerobic metabolism in anoxic conditions, thus allowing Neodasys to exploit a different niche.

     

Respiration in the eastern water dragon,Physignathus lesueurii (agamidae)

• 1.1. Some aspects of the gas exchange system of a diving lizard, Physignathus lesuewii were studied.
• 2.2. Breathing patterns were analysed.
• 3.3. Breathing rate increases logarithmically with temperature and Q₁₀ = 1.8. LogBR = −0.237 + 0.0256 T.
• 4.4. Gas tensions in lung air and arterial and venous blood were measured. Arterial pH declines with increasing temperature.
• 5.5. Temperature has a marked effect on oxygen affinity of the blood (ΔH = −10.1 kcal mol⁻). A Bohr effect was also noted.
• 6.6. CO₂ equilibrium curves were drawn.
• 7.7. The results are considered with a view to anticipating the efficiency of the gas exchange system of this species under conditions of variable temperature and during diving.

     

The effects of acclimatization on body weight and oxygen consumption in Dipodomys panamintinus

• 1.1. Seasonal acclimatization effects on oxygen consumption, body temperature, and body weight were evaluated in three different experimental groups of Dipodomys panamintinus.
• 2.2. Body weights of wild field as well as captive animals housed in outdoor sand cages were maximum in winter and lowest in summer for both sexes.
• 3.3. Mean oxygen consumption was maximum in winter and lowest during spring in both sexes of the wild field and captive exposed groups.
• 4.4. Neither weight nor oxygen consumption of indoor control animals varied with the seasons.
• 5.5. No significant differences in body temperatures were observed during either the fall or winter seasons.

     

Measurements of oxygen consumption in Mytilus edulis during exposure to,and recovery from,high sublethal concentrations of formaldehyde,benzene and phenol

• 1.1. The rate of oxygen consumption has been monitored continuously in M. edulis during acute exposure to high sublethal concentrations of formaldehyde, phenol and benzene and subsequent recovery periods of 96 hr.
• 2.2. The results are discussed in relation to changes in the electrochemical potential difference of sodium, the content of ATP and the tissue concentration of strombine.
• 3.3. After exposure to benzene and phenol, an increase in the rate of oxygen consumption that could not be explained by oxygen debt from the exposure period was observed.
• 4.4. Depression of the rate of oxygen consumption after exposure to formaldehyde may be explained by a reduced ability to extract oxygen from the water.
• 5.5. The pattern of oxygen consumption and behavioural responses, as well as the combined changes in the biochemical markers, were distinctly different in the three cases.

     

Effects of anoxia on the haemolymph physiology and lactate concentrations in the freshwater crab Potamon warreni calman

• 1.1. Haemolymph lactate levels rose rapidly from 0.54 ( ± 0.39) mmol to 34.78 ( ± 4.9) mmol during 6 hr of anoxia in a N₂ atmosphere.
• 2.2. A sharp decrease in the pH from 7.478 (± 0.04) to 7.197 ( ± 0.04) and the total carbon dioxide content of the haemolymph from 13.97 (± 2.0) mmol to 6.25 (± 1.2) mmol during anoxia indicates a gross disturbance in the acid-base balance in Potamon warreni.
• 3.3. The low concentrations of succinate (98 ± 30 μmol) and alanine (5.8 ± 1.0 mmol) in the haemolymph suggest that they do not play a role as an energy source during anoxia.
• 4.4. Probably only l-( + )-lactate is produced during lactate production when P. warreni is exposed to anoxic conditions.

     

Laboratory studies on the oxygen consumption of the marine teleost,Lichia amia (Linnaeus, 1758)

• 1.1. The oxygen consumption of the marine teleost, Lichia amia was investigated under controlled laboratory conditions.
• 2.2. The routine oxygen consumption showed a strong circadian rhythm with the fish being mainly active during the light period.
• 3.3. The specific mass exponent (dimension: μg O₂/g/hr) is temperature independent and ranges from 0.27–0.29.
• 4.4. Starving the fish results in a mean decrease in active, routine and standard oxygen consumption of 21%, 24% and 20%, respectively.
• 5.5. Feecling led to an increase in the oxygen consumption of the teleosts, with the mean metabolic rate over the 24 hr that followed, being 58% and 50% higher for fish that had been starved for 162hr and 40 hr, respectively.
• 6.6. Apparent SDA showed some variation and ranged from 6.0 to 35.5%.
• 7.7. The results obtained are generally in agreement with those recorded for other teleosts.

     

Responses of antioxidants and lipid peroxidation in mussels to oxidative damage exposure

• 1.1. The aim of this work was to evaluate the relationships between free radical scavengers and lipid peroxidation in the common mussel Mytilus edulis.
• 2.2. Mussels were exposed to compounds known for their ability to produce free radicals (carbon tetrachloride, CCl₄) and reactive oxygen species via redox cycling (menadione), and the effects on digestive gland, gills and remaining tissues were studied.
• 3.3. Lipid peroxidation parameters and the status of free radical scavengers (glutathione, vitamins A, E and C) were affected more by exposure to menadione than to CCl₄.
• 4.4. The observed changes in the free radical scavengers content are indicative of a role in detoxication of damaging reactive species.

     

Effect of temperature and salinity on the oxygen consumption of laboratory produced Penaeus californiensis postlarvae

• 1.1. The oxygen consumption by P. californiensis postlarvae (mean wt = 0.38 g) was determined at five different temperatures and four salinities.
• 2.2. The O₂ in each chamber was recorded at 10 min intervals for 1 hr. The time course of oxygen depletion was independent of O₂ concentration down to 1.6 mg/l.
• 3.3. Oxygen consumption increased with temperature from 0.0045 mg/g/min at 19°C, to 0.0142 mg/g/min at 35°C. The thermal coefficient (Q₁₀) indicated a very high sensitivity of the postlarvae to temperature variations at 19–23°C.
• 4.4. The results show that oxygen consumption significantly depends on temperature (P < 0.001) while salinity has only a marginal effect.

     

Variations in response to environmental hypoxia of different colour forms of the shore crab,Carcinus maenas

• 1.1. The oxygen consumption of red and green Carcinus in normoxic and hypoxic sea water was determined, using an oxygen electrode in a sealed respirometer.
• 2.2. The red crabs had significantly higher “excited” oxygen uptake rates and a lower ability to compensate for hypoxia than the green crabs.
• 3.3. Red Carcinus display an emersion response to declining oxygen at lower oxygen tensions than the green crabs.
• 4.4. Mortality of red crabs exposed to prolonged anoxia was much greater.
• 5.5. The relationship of these findings to the zonation of the two colour forms on the shore is discussed.

     

The effect of a toxic dinoflagellate (Alexandrium tamarense) on the oxygen uptake of juvenile filter-feeding bivalve molluscs

• 1.1. Oxygen uptake and grazing rates of juvenile bivalve molluscs Mytilus edulis, Mya arenaria, Geukensia demissa, Placopecten magellanicus and Crassostrea virginica were measured following 1 hr exposure to bloom concentrations (10⁶ cells/1) of the toxic dinoflagellate Alexandrium tamarense (GT429) using a non-toxic clone of the same species (PLY 173) as control.
• 2.2. For all bivalves, prefeeding estimates of V̇O₂ were similar to postfeeding values and values recorded 24 hr after exposure to bloom conditions.
• 3.3. V̇O₂ was similar for bivalves fed on both the toxic and non-toxic strains of A. tamarense suggesting that there were no adverse effects on V̇O₂ following 1 hr exposure to toxic GT429.
• 4.4. Bivalves differed in their rates of grazing between toxic GT429 and non-toxic PLY 173. Similar grazing rates were recorded for M. edulis and G. demissa. For P. magellanicus and M. arenaria reduced rates of clearance were recorded in GT429 compared with the non-toxic strain.

     

The effect of low levels of carbon dioxide on metabolism of Mus musculus

• 1.1. In this study we measured the metabolic response of individual mice to low concentrations of carbon dioxide in air (0.14 to 1.7%). Both oxygen consumption (V_o2) and carbon dioxide (V_o2) were determined, and the respiratory quotient (R) was calculated.
• 2.2. V_o2 was significantly reduced at levels of 0.14 to 0.50% CO₂ in the air. At 0.23% for example, V_o2 dropped from 3.11 ± 0.6 to 1.26 ± 0.69 cc O₂/g × hr. R increased from 0.7 to 1.0 and higher throughout the 6-hr testing period, which consisted of 1.5 hr of exposure to 0.0% CO₂, 1.5 hr of exposure to a test gas and a repetition of 1.5 hr each of baseline and test exposures.
• 3.3. We conclude that low levels of CO₂ such as mice might encounter in a nest, burrow or even metabolic chamber may effect a feedback mechanism which acts to decrease metabolism.

     

Synaptic transmission at high pressure: Effects of [Ca2+]o

• 1.1. The effects of pressure on synaptic currents were examined in crayfish abdominal muscles.
• 2.2. Helium pressure (10.1 MPa) considerably decreased extracellulariy-recorded excitatory junctional potentials associated with increased short-term facilitation.
• 3.3. These effects could be mimicked by a reduction of [Ca²⁺]_o, and partially compensated by an increase in [Ca²⁺]_o.
• 4.4. Pressure also reduced the amplitude of the extracellular nerve terminal potentials (ENTP) by up to 25%, and significantly increased synaptic delay in a [Ca²⁺]_o-dependent manner.
• 5.5. The interaction between compression and various [Ca²⁺]_o were analysed in terms of an existing model of transmitter release. The results were consistent with the hypothesis that high pressure decreases the maximal Ca²⁺ influx into nerve terminals.
• 6.6. The decreased ENTP and increased synaptic delay suggest that additional processes may be involved in pressure effects on synaptic transmission.

     

Comparative study of hemoglobins from different Artemia populations. The influence of temperature on the oxygen equilibria

• 1.1. The P50 values of extracellular hemoglobin (Hb) of five Artemia populations from different geographical origin are affected by temperature.
• 2.2. The free oxygen binding energy is high for all the populations (ΔH between −34.7 and −56.2kj/mol).
• 3.3. A possible correlation between thermal sensitivity of Hb and the ambient temperature of the habitat must be considered very carefully.
• 4.4. The occurence of different quantities of Hb1 (αα chains) Hb2 (αβ chains) and Hb3 (ββ chains) in the different populations possibly influences thermal sensitivity.