Characterization of an ecto-ATPase activity in Fonsecaea pedrosoi

In this work, we characterized an ecto-ATPase activity in intact mycelial forms of Fonsecaea pedrosoi, the primary causative agent of chromoblastomycosis. In the presence of 1 mM EDTA, fungal cells hydrolyzed adenosine-5′-triphosphate (ATP) at a rate of 84.6 ± 11.3 nmol Pi h⁻¹ mg⁻¹ mycelial dry weight. The ecto-ATPase activity was increased at about five times (498.3 ± 27.6 nmol Pi h⁻¹ mg⁻¹) in the presence of 5 mM MgCl₂, with values of V _max and apparent K _m for Mg-ATP²⁻corresponding to 541.9 ± 48.6 nmol Pi h⁻¹ mg⁻¹ cellular dry weight and 1.9 ± 0.2 mM, respectively. The Mg²⁺-stimulated ecto-ATPase activity was insensitive to inhibitors of intracellular ATPases such as vanadate (P-ATPases), bafilomycin A₁ (V-ATPases)_, and oligomycin (F-ATPases). Inhibitors of acid phosphatases (molybdate, vanadate, and fluoride) or alkaline phosphatases (levamizole) had no effect on the ecto-ATPase activity. The surface of the Mg²⁺-stimulated ATPase in F. pedrosoi was confirmed by assays in which 4,4′-diisothiocyanostylbene-2,2′-disulfonic acid (DIDS), a membrane impermeant inhibitor, and suramin, an inhibitor of ecto-ATPase and antagonist of P₂ purinoreceptors. Based on the differential expression of ecto-ATPases in the different morphological stages of F. pedrosoi, the putative role of this enzyme in fungal biology is discussed.     

Metabolic energy utilization during development of Antarctic naked dragonfish (Gymnodraco acuticeps)

We have capitalised on the availability of eggs and adults of the naked dragonfish Gymnodraco acuticeps (Sub-order Notothenioidei, F. Bathydraconidae) near McMurdo Station, Antarctica to examine metabolic energy utilization at different stages of its life cycle. Average egg respiration rates were found to increase from 2.17±1.02 nmol O₂ h⁻¹ ind⁻¹ at about 17 h post-fertilization (hpf) to 5.72±0.56 nmol h⁻¹ ind⁻¹ at about 24 hpf, during which time the eggs underwent first cleavage. The respiration rates of embryos from 2–20 days post-fertilization (dpf) averaged 4.11±1.47 nmol O₂ h⁻¹ ind⁻¹. About 10 months post-fertilization, oxygen consumption rates of 27.14±3.92 nmol O₂ h⁻¹ ind⁻¹ were recorded immediately prior to hatching, with a peak of 112.41±31.38 nmol O₂ h⁻¹ ind⁻¹ at the time of hatch. Larvae aged 46–63 days post-hatch had an average respiration rate of 64.4±15.11 nmol O₂ h⁻¹ ind⁻¹. Mass-specific respiration rates of hatched larvae (approximately 1–2 months old) were calculated using dry weights (DW) and averaged 16.1±3.4 nmol O₂ h⁻¹ mg⁻¹ DW. Adult dragonfish respiration rates (corrected for a 100 g fish and using a 0.8 scaling exponent) averaged 0.91±0.36 mmol O₂ kg⁻¹ h⁻¹ after a 48 h acclimatization period, which is not indicative of significant metabolic cold adaptation. The energy contents of dragonfish eggs and larvae were also measured by microbomb calorimetry and used, along with the respiration data, in an initial approach to estimate an energy budget. In order to balance the budget, the bulk of the available post-gastrulation respiratory energy (during 213 days of embryonic incubation) must be consumed at a relatively low average rate (7.1 nmol O₂ h⁻¹ ind⁻¹), which supports the possibility that advanced dragonfish embryos overwinter in a relatively quiescent metabolic state while awaiting a suitable stimulus (such as the return of the sun) to initiate hatching.     

Oxygen consumption by ammocoetes of the lampreyGeotria australis in air

 When covered by moistened lint-free gauze, the larvae (ammocoetes) of the lamprey Geotria australis survived, without apparent discomfort, for 4 days in water-saturated air at 10, 15 and 20 °C. In air, the mean standard rates of O₂ consumption of medium to large ammocoetes of G. australis (xˉ=0.52 g) at 10, 15 and 20 °C were 14.5, 35.7 and 52.1 μl⋅g^-1⋅h^-1, respectively. At 15 °C, the slope of the relationship between log O₂ consumption (μl O₂⋅h^-1) and log body weight for ammocoetes over a wide range in body weight was 0.987. The Q ₁₀s for rate of O₂ consumption between 10 and 15 °C, 15 and 20 °C and 10 and 20 °C were 4.9, 2.9 and 3.6, respectively. Our results and observations of the ammocoetes suggest that, when out of water, larval G. australis derives most of its O₂ requirements from cutaneous respiration, particularly at lower temperatures. This would be facilitated by the small size and elongate shape (and thus a relatively high surface-to-volume ratio), low metabolic rate, thin dermis, extensive subdermal capillary network and high haemoglobin concentration of larval G. australis. Accepted: 28 March 1996     

Effect of meal size on the specific dynamic action of the juvenile snakehead (Channa argus)

The effect of meal size on the specific dynamic action (SDA) of the juvenile snakehead (Channa argus) was assessed at 25 °C. The fish were fed with test diets at meal sizes of 0.5, 1, 2, 3, 4, and 5% body mass and the postprandial oxygen consumption rate was determined at 1-h intervals until it returned to the pre-prandial level. The peak metabolic rate increased from 237.4 to 283.2 mg O₂ kg^− 1 h^− 1 as the relative meal size increased from 0.5% to 3% and leveled off at 4% and 5%. Factorial metabolic scope increased from 1.53 to 1.99 and SDA duration increased from 11.7 to 32.3 h as the relative meal size increased from 0.5% to 5%. The relationship between SDA duration (D) and relative meal size (M) was described as: D = 4.28 M + 10.62 (r² = 0.752, P < 0.05, n = 50). The energy expended on SDA increased while the SDA coefficient decreased with increasing meal size. The results of the present study suggest that the snakehead may adopt different feeding strategies when taking in different amounts of food.     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

Activity,milk intake and energy consumption in free-living ringed seal (Phoca hispida) pups

Measurements of growth, activity and energy consumption and estimates of milk intake were made in free-living, nursing ringed seal (Phoca hispida) pups. This was accomplished through the simultaneous use of time-depth recorders and the doubly labelled water technique. The pups spent an average of 52±7% of their time hauled out on the ice, 37±5% of the time in the water at the surface, and 11±5% of the time diving. Average daily mass gain of the pups (n=3) throughout the duration of the study period was 0.35±0.08 kg. The composition of the mass gain was 76% fat, 6% protein and 18% water. The total water flux was measured to be 52±10 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.16 ml·g^-1·h^-1, corresponding to a field metabolic rate of 0.55±0.10 MJ·kg^-1·day^-1, or 3.8±0.6 times the predicted basal metabolic rate based on body size (Kleiber 1975). Average daily milk intake was estimated to be 1379±390 ml. The field metabolic rate for the different components of seal pup activity budgets were calculated to be FMR_{haul out}=1.34 BMR, FMR_surface=6.44 BMR, and FMR_diving=5.88 BMR.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - HTO tritiated water - HT¹⁸O doubly labelled water - RQ respiration quotient - SDA specific dynamic action - TDR time-depth recorder     

Kinetics of urea uptake by Melosira italica (Ehr.) Kütz at different luminosity conditions

The kinetic parameters K_m and V_max for urea uptake by Melosira italica were determined at 160 μeinsteins m⁻² s⁻¹ and in the dark. The transport systems showed an affinity for the substrate and a storing capacity in the dark (K_m = 65.07 μM; V_max = 2.18 nmoles 10⁵ cells ⁻¹ h⁻¹) greater than under 160 μE m⁻² s ⁻¹ (K_m = 111.2 μM; V_max = 1.11 nmoles 105 cells⁻¹ h⁻¹). Similarly, a reduction in consumption rate of urea under increasing photon flux densities was observed. The use of an inhibitor (potassium cyanide) indicated that the uptake process requires metabolic energy. That urea transport is more important in darkness, may constitute a survival strategy in which this compound is utilized by cells mainly during heterotrophic growth.     

The effect of temperature on the pattern of torpor in a marsupial hibernator

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2°C. The duration of torpor bouts was longest (14.0±1.0 days) and metabolic rate was lowest (0.033±0.001 ml O₂·g^-1·h^-1) at2°C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0°C, torpor bouts also shortened to 6.4±2.9 days, metabolic rate increased to about eight-fold the values at 2°C, and body temperature was maintained at the regulated minimum of 2.1±0.2°C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.Abbreviationst STP standard temperature and pressure - T _a air temperature - T _b body temperature - VO₂ rate of oxygen consumption     

Influence of agitation and aeration on growth and antibiotic production by <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis>

The effect of agitation and aeration on the growth and antibiotic production by Xenorhabdus nematophila YL001 grown in batch cultures were investigated. Efficiency of aeration and agitation was evaluated through the oxygen mass transfer coefficient (K _L a). With increase in K _L a, the biomass and antibiotic activity increased. Activity units of antibiotic and dry cell weight were increased to 232 U ml⁻¹ and 19.58 g l⁻¹, respectively, productivity in cell and antibiotic was up more than 30% when K _L a increased from 115.9 h⁻¹ to 185.7 h⁻¹. During the exponential growth phase, DO concentration was zero, the oxygen supply was not sufficient. So, based on process analysis, a three-stage oxygen supply control strategy was used to improved the DO concentration above 30% by controlling the agitation speed and aeration rate. The dry cell weight and activity units of antibiotic were further increased to 24.22 g l⁻¹ and 249 U ml⁻¹, and were improved by 24.0% and 7.0%, compared with fermentation at a constant agitation speed and a constant aeration rate (300 rev min⁻¹, 2.5 l min⁻¹).     

Production of inulinase by solid-state fermentation: effect of process parameters on production and preliminary characterization of enzyme preparations

This work was aimed at producing inulinase by solid-state fermentation of sugarcane bagasse, using factorial design to identify the effect of corn steep liquor (CSL) and soybean bran concentration, particle size of bagasse and size of inoculum. Maximum inulinase activity achieved was 250 U per g of dry substrate (gds) at 20% (w/w) of CSL, 5% (w/w) of soybean bran, 1 × 10¹⁰ cells mL⁻¹ and particle size of bagasse in the range 9/32 mesh. The use of soybean bran decreased the time to reach maximum activity from 96 to 24 h and the maximum productivity achieved was 8.87 U gds⁻¹ h⁻¹. The maximum activity was obtained at pH 5.0 and 55.0°C. Within the investigated range, the enzyme extract was more thermostable at 50.0°C, showing a D-value of 123.1 h and deactivation energy of 343.9 kJ gmol⁻¹. The extract showed highest stability from pH 4.5 to 4.8. Apparent K _m and V _max are 7.1 mM and 17.79 M min⁻¹, respectively.     

Adaptive mechanisms during food restriction in <Emphasis Type="Italic">Acomys russatus</Emphasis>: the use of torpor for desert survival

The golden spiny mouse (Acomys russatus) is an omnivorous desert rodent that does not store food, but can store large amounts of body fat. Thus, it provides a good animal model to study physiological and behavioural adaptations to changes in food availability. The aim of this study was to investigate the time course of metabolic and behavioural responses to prolonged food restriction. Spiny mice were kept at an ambient temperature of 27°C and for 3 weeks their food was reduced individually to 30% of their previous ad libitum food intake. When fed ad libitum, their average metabolic rate was 82.77±3.72 ml O₂ h^–1 during the photophase and 111.19±4.30 ml O₂ h^–1 during the scotophase. During food restriction they displayed episodes of daily torpor when the minimal metabolic rate gradually decreased to 16.07±1.07 ml O₂ h^–1, i.e. a metabolic rate depression of approximately 83%. During the hypometabolic bouts the minimum average body temperature T_b, decreased gradually from 32.6±0.1°C to 29.0±0.4°C, with increasing duration of consecutive bouts. In parallel, the animals increased their activity during the remaining daytime. Torpor as well as hyperactivity was suppressed immediately by refeeding. Thus golden spiny mice used two simultaneous strategies to adapt to shortened food supply, namely energysaving torpor during their resting period and an increase in locomotor activity pattern during their activity period.     

Chronic Atmospheric NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> Deposition Does Not Induce NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> Use by <Emphasis Type="Italic">Acer saccharum</Emphasis> Marsh.

The ability of an ecosystem to retain anthropogenic nitrogen (N) deposition is dependent upon plant and soil sinks for N, the strengths of which may be altered by chronic atmospheric N deposition. Sugar maple (Acer saccharum Marsh.), the dominant overstory tree in northern hardwood forests of the Lake States region, has a limited capacity to take up and assimilate NO₃⁻. However, it is uncertain whether long-term exposure to NO₃⁻ deposition might induce NO₃⁻ uptake by this ecologically important overstory tree. Here, we investigate whether 10 years of experimental NO₃⁻ deposition (30 kg N ha⁻¹ y⁻¹) could induce NO₃⁻ uptake and assimilation in overstory sugar maple (approximately 90 years old), which would enable this species to function as a direct sink for atmospheric NO₃⁻ deposition. Kinetic parameters for NH₄⁺ and NO₃⁻ uptake in fine roots, as well as leaf and root NO₃⁻ reductase activity, were measured under conditions of ambient and experimental NO₃⁻ deposition in four sugar maple-dominated stands spanning the geographic distribution of northern hardwood forests in the Upper Lake States. Chronic NO₃⁻ deposition did not alter the V _max or K _m for NO₃⁻ and NH₄⁺ uptake nor did it influence NO₃⁻ reductase activity in leaves and fine roots. Moreover, the mean V _max for NH₄⁺ uptake (5.15 μmol ¹⁵N g⁻¹ h⁻¹) was eight times greater than the V _max for NO₃⁻ uptake (0.63 μmol ¹⁵N g⁻¹ h⁻¹), indicating a much greater physiological capacity for NH₄⁺ uptake in this species. Additionally, NO₃⁻ reductase activity was lower than most values for woody plants previously reported in the literature, further indicating a low physiological potential for NO₃⁻ assimilation in sugar maple. Our results demonstrate that chronic NO₃⁻ deposition has not induced the physiological capacity for NO₃⁻ uptake and assimilation by sugar maple, making this dominant species an unlikely direct sink for anthropogenic NO₃⁻ deposition.     

Effects of body lipid content on the resting metabolic rate and postprandial metabolic response in the southern catfish Silurus meridionalis

We assessed the effects of body lipid content on the resting metabolic rate and specific dynamic action (SDA) of the southern catfish Silurus meridionalis. Obese and lean fish were obtained by feeding the fish with two different feeds at 27.5 °C for 4 weeks prior to the experiment. The fish were fed with experimental diets with a meal size of 4% by body mass. A continuous-flow respirometer was used to determine the oxygen consumption rate at 2-h intervals until the postprandial oxygen consumption rate had returned to the preprandial level. The body lipid content of the obese fish was significantly greater than that of the lean fish. The metabolic parameters evaluated (resting metabolic rate, peak metabolic rate (R_peak), factorial ratio, time to peak, duration, energy expended on SDA (SDA_E), or SDA coefficient) were not significantly affected by body fat content in terms of the whole-body or mass-specific values. Increased body fat content did not decrease the resting metabolic rate in the southern catfish, which might be due to the higher levels of highly unsaturated fatty acids in these fish. The results also suggest that the body composition does not appear to affect the SDA response.     

Enhancement of xylitol productivity and yield using a xylitol dehydrogenase gene-disrupted mutant of Candida tropicalis under fully aerobic conditions

The effects of glycerol and the oxygen transfer rate on the xylitol production rate by a xylitol dehydrogenase gene (XYL2)-disrupted mutant of Candida tropicalis were investigated. The mutant produced xylitol near the almost yield of 100% from d-xylose using glycerol as a co-substrate for cell growth and NADPH regeneration: 50 g d-xylose l⁻¹ was completely converted into xylitol when at least 20 g glycerol l⁻¹ was used as a co-substrate. The xylitol production rate increased with the O₂ transfer rate until saturation and it was not necessary to control the dissolved O₂ tension precisely. Under the optimum conditions, the volumetric productivity and xylitol yield were 3.2 g l⁻¹ h⁻¹ and 97% (w/w), respectively.     

Temporal variation in CO<Subscript>2</Subscript> efflux from soil and snow surfaces in a Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) plantation,central Japan

CO₂ efflux from soil and snow surfaces was measured continuously in a Japanese cedar (Cryptomeria japonica D. Don) forest in central Japan using an open dynamic chamber system. The chamber opens and closes automatically and records measurements based on an open-flow dynamic method. Between May and December, mean soil CO₂ efflux ranged from 1,529 mg CO₂ m⁻² h⁻¹ in September to 255 mg CO₂ m⁻² h⁻¹ in December. The seasonal change in CO₂ efflux from the soil paralleled the seasonal pattern of soil temperature. No marked diurnal trends in soil CO₂ efflux were observed on days without rainfall, whereas significant pulses in soil CO₂ efflux were observed on days with rainfall. In this plantation, soil CO₂ efflux frequently responded to rainfall. Measurements of changes from litter-covered soil to snow-covered surfaces revealed that CO₂ efflux decreased from values of ca. 250 mg CO₂ m⁻² h⁻¹ above soil to less than 33 mg CO₂ m⁻² h⁻¹ above snow. Soil temperature alone explained 66% of the overall variation in soil CO₂ efflux, but explained approximately 85% of the variation when data from two anomalous periods were excluded. Moreover, we found a significant correlation between soil CO₂ efflux and soil moisture (which explained 44% of the overall variation) using a second-order polynomial function. Our results suggest that the seasonality of CO₂ efflux is affected not only by soil temperature and moisture, but also by drying and rewetting cycles and by litterfall pulses.     

Metabolism and thermoregulation in the eastern hedgehogErinaceus concolor

Body temperature and oxygen consumption were measured in the eastern hedgehog,Erinaceus concolor Martin 1838, during summer at ambient temperatures (T _a) between-6.0 and 35.6°C.E. concolor has a relatively low basal metabolic rate (0.422 ml O₂·g^-1·h^-1), amounting to 80% of that predicted from its body mass (822.7 g). Between 26.5 and 1.2°C, the resting metabolic rate increases with decreasing ambient temperature according to the equation: RMR=1.980-0.057T _a. The minimal heat transfer coefficient (0.057 ml O₂·g^-1·h^-1·°C^-1) is higher than expected in other eutherian mammals, which may result from partial conversion of hair into spines. At lower ambient temperature (from-4.6 to-6.0° C) there is a drop in body temperature (from 35.2 to 31.4° C) and a decrease in oxygen consumption (1.530 ml O₂·g^-1·h^-1) even though the potential thermoregulation capabilities of this species are significantly higher. This is evidenced by the high maximum noradrenaline-induced non-shivering thermogenesis (2.370 ml O₂·g^-1·h^-1), amounting to 124% of the value predicted. The active metabolic rate at ambient temperatures between 31.0 and 14.5° C averages 1.064 ml O₂·g^-1·h^-1; at ambient temperatures between 14.5 and 2.0° C AMR=3.228-0.140T _a.Abbreviations AMR active metabolic rate - bm body mass - BMR basal metabolic rate - h heat transfer coefficient - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum rate of NA-induced non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - STPD standard temperature and pressure (25°C, 1 ATM) - T _a ambient temperature - T _b body temperature     

Milk intake,growth and energy consumption in pups of ice-breeding grey seals (Halichoerus grypus) from the Gulf of St. Lawrence,Canada

In this study we document growth, milk intake and energy consumption in nursing pups of icebreeding grey seals (Halichoerus grypus). Change in body composition of the pups, change in milk composition as lactation progresses, and mass transfer efficiency between nursing mothers and pups are also measured. Mass transfer efficiency between mother-pup pairs (n=8) was 42.5±8.4%. Pups were gaining a daily average of 2.0±0.7 kg (n=12), of which 75% was fat, 3% protein and 22% water. The total water influx was measured to be 43.23±8.07 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.20 ml·g^-1·h^-1, which corresponds to a field metabolic rate of 0.55±0.13 MJ·kg^-1·day^-1, or 4.5±0.9 times the predicted basal metabolic rate based on body size (Kleiber 1975). Water and fat content in the milk changed dramatically as lacation progressed. At day 2 of nursing, fat and water content were 39.5±1.9% and 47.3±1.5%, respectively, while the corresponding figures for day 15 were 59.6±3.6% fat and 28.4±2.6% water. Protein content of the milk remained relatively stable during the lactation period with a value of 11.0±0.8% at day 2 and 10.4±0.3% at day 15. Pups drank an average of 3.5±0.9 kg of milk daily, corresponding to a milk intake of 1.75 kg per kg body mass gained. The average daily energy intake of pups was 82.58±19.80 MJ, while the energy built up daily in the tissue averaged 61.72±22.22 MJ. Thus, pups assimilated 74.7% of the energy they received via milk into body tissue. The lactation energetics of ice-breeding grey seals is very similar to that of their land-breeding counterparts.Abbreviations bm body mass - BMR basal metabolic rate - FMR field metabolic rate - IU international unit - RQ respiration quotient - HTO tritiated water - HT¹⁸O doubly labeled water - TBW total body water - VHF very high frequency     

Decalactone Production by <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> under increased O<Subscript>2</Subscript> Transfer Rates

Yarrowia lipolytica converts methyl ricinoleate to γ-decalactone, a high-value fruity aroma compound. The highest amount of 3-hydroxy-γ-decalactone produced by the yeast (263 mg l^-1) occurred by increasing the k_La up to 120 h⁻¹ at atmospheric pressure; above it, its concentration decreased, suggesting a predominance of the activity of 3-hydroxyacyl-CoA dehydrogenase. Cultures were grown under high-pressure, i.e., under increased O₂ solubility, but, although growth was accelerated, γ-decalactone production decreased. However, by applying 0.5 MPa during growth and biotransformation gave increased concentrations of dec−2-en-4-olide and dec-3-en-4-olide (70 mg l⁻¹).     

Thermoregulation in three species of Afrotropical subterranean mole-rats (Rodentia: Bathyergidae) from Zambia and Angola and scaling within the genus Cryptomys

The thermoregulatory characteristics of three species of Cryptomys from Zambia and Angola are examined and, together with published data on four other species of Cryptomys from southern Africa, used to determine whether scaling occurs in this genus of subterranean rodents. The thermoregulatory properties of acclimated giant Zambian mole-rats, Cryptomys mechowi ( =267 g), Angolan mole-rats, Cryptomys bocagei ( =94 g) and Zambian common mole-rats Cryptomys hottentotus amatus ( =77 g) are as follows. Mean resting metabolic rates (RMRs) within the respective thermoneutral zones were 0.60±0.08 cm³ O₂ g^-1 h^-1 (n=12) for C. mechowi; 0.74±0.06 cm³ O₂ g^-1 h^-1 (n=8) for C. bocagei and 0.63±0.06 cm³O₂ g^-1 h^-1 (n=21) for C. h. amatus. The thermoneutral zones (TNZs) of all three species are narrow: 29–30°C for C. mechowi; 31.5–32.5°C for C. bocagei and 28–32° C for C. h. amatus. The increase in mean RMR at the lowest temperatures tested (15° C for C. mechowi, 18° C for C. bocagei and C. h. amatus) was 2.35, 2.2 and 3.82 times their RMR in the TNZ respectively. Body temperatures are low, 34±0.53° C (n=24) for C. mechowi, 33.7±0.32° C (n=20) for C. bocagei and 33.8±0.43° C (n=40) for C. h amatus. At the lower limit of thermoneutrality, conductances are 0.09±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=30) in C. mechowi; 0.12±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=20) in C. bocagei and 0.12±0.03 cm³ O₂ g^-1 h^-1 °C^-1 (n=32) in C. h. amatus. The range in mean body mass among the seven species of Cryptomys examined for scaling was 60 g (C. darlingi) to 267 g (C. mechowi). There is no clear relationship between RMR within the TNZ and body mass. The resultant relationship is represented by the power curve RMR=2.45 mass^-0.259.     

Oxygen consumption and blood flow distribution in perfused skeletal muscle of chinook salmon

An isolated, perfused salmon tail preparation showed oxyconformance at low oxygen delivery rates. Addition of pig red blood cells to the perfusing solution at a haematocrit of 5 or 10% allowed the tail tissues to oxyregulate. Below ca. 60 ml O₂ kg⁻¹ h⁻¹ of oxygen delivery (DO₂), VO₂ was delivery dependent. Above this value additional oxygen delivery did not increase VO₂ of resting muscle above ca. 35 ml O₂ kg⁻¹ h⁻¹. Following electrical stimulation, VO₂ increased to ca. 65 ml O₂ kg⁻¹ h⁻¹, with a critical DO₂ of ca. 150 ml O₂ kg⁻¹ h⁻¹. Dorsal aortic pressure fell to 69% of the pre-stimulation value after 5 min of stimulation and to 54% after 10 min. Microspheres were used to determine blood flow distribution (BFD) to red (RM) and white muscle (WM) within the perfused myotome. Mass specific BFD ratio at rest was found to be 4.03 ± 0.49 (RM:WM). After 5 min of electrical stimulation the ratio did not change. Perfusion with saline containing the tetrazolium salt 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) revealed significantly more mitochondrial activity in RM. Formazan production from MTT was directly proportional to time of perfusion in both red and WM. The mitochondrial activity ratio (RM:WM) did not change over 90 min of perfusion.