Turnover of the fatty acyl and glycerol moieties of microsomal membrane lipids from liver, gill and muscle tissue of thermally acclimated rainbow trout,Salmo gairdneri

Summary Rainbow trout (Salmo gairdneri) acclimated to 5°C or 20°C were administered 2-³H-glycerol and 1-¹⁴C-acetate (63 Ci of each isotope/100 g body weight) via intraperitoneal injection, and subsequently maintained at their respective acclimation temperatures. Total lipid extracts (>80% phospholipid) were prepared from isolated microsomes of liver, gill and muscle tissue at various times over a three week period. Half-lives were determined independently for the fatty acyl and glycerol moieties from slopes of regression lines relating dpm/nmole phospholipidP _i vs time. In liver tissue, rates of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) turnover were also determined. Membrane turnover was most rapid in liver followed by gill and muscle. In liver, membrane fatty acids turned over more rapidly in warm-(t _1/2=3.4 days) than in cold-(t _1/2=6.8 days) acclimated fish, whereas in gill, rates of fatty acid turnover, did not differ significantly between acclimation groups. In contrast, rates of glycerol turnover were independent of acclimation temperature in liver, but faster (t _1/2=6.7 days) in warm- than cold- (t _1/2=15.1 days) acclimated fish in gill. In total lipid extracts, rates of fatty acid and glycerol turnover were equivalent in warm-acclimated fish, however, in cold-acclimated trout, there was a tendency for fatty acids (t _1/2=9.1 days) to turnover more rapidly than glycerol (t _1/2=15.1 days) in gill tissue, but more slowly (t _1/2=6.82 days) than glycerol (t _1/2=4.1 days) in liver. Although rates of glycerol turnover were equivalent in PC and PE of liver microsomes, the fatty acyl component turned over significantly more rapidly in PC at both acclimation temperatures. In cold-acclimated trout, rates of fatty acid and glycerol turnover were equivalent in PE, but the fatty acyl moiety of PC (t _1/2=4.7 days) turned over significantly more rapidly than glycerol (t _1/2=7.5 days). These results were interpreted as indicating that: (1) acclimation temperature independently influenced rates of fatty acid and glycerol turnover in a tissue specific manner, (2) a deacylation-reacylation pathway was activated in both liver and gill as a consequence of cold acclimation, but that liver tissue was more effective than gill in reutilizing the fatty acids released by phospholipase activity, and (3), in liver microsomes, patterns of turnover were phospholipid specific, with PC and PE differing either in the susceptibility of their acyl groups to degradation, or in their ability to reutilize fatty acids cleaved during membrane turnover at cold temperatures.     

Thermoacclimatory changes in blood oxygen binding properties and gill secondary lamellar structure ofSalmo gairdneri

Summary The blood oxygen binding properties and gill secondary lamellar structure of rainbow trout acclimated to several temperatures were studied. The blood oxygen carrying capacity decreased as acclimation temperature increased from 2 to 15 °C; the decrease was probably caused by an increase in plasma volume. Also the blood oxygen affinity decreased as the acclimation temperature increased from 2 to 15 °C. This change had no effect on the oxygen loading in gills, since the efferent arterial oxygen tension was adequate for approximately 100% erythrocytic O₂ saturation at all acclimation temperatures, but facilitated the oxygen unloading in tissues. At the highest acclimation temperature (18 °C) the oxygen loading in gills was facilitated by the changes in the secondary lamellar structure; the proportion of erythrocytes in the secondary lamellar capillaries was higher than at the other acclimation temperatures (2 and 10 °C).     

Thermal adaptation in biological membranes: interacting effects of temperature and pH

Summary The interacting effects of pH and temperature on membrane fluidity were studied in plasma membranes isolated from liver of rainbow trout (Oncorhynchus mykiss) acclimated to 5 and 20°C. Fluidity was determined as a function of temperature under conditions of both constant (in potassium phosphate buffer) and variable pH (in imidazole buffer, consistent with imidazole alphastat regulation) from the fluorescence anisotropy of two probes: 1,6-diphenyl-1,3,5-hexatriene, which intercalates into the bilayer interior, and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene which is anchored at the membrane/water interface. The temperature dependence of the anisotropy parameter for 1,6-diphenyl-1,3,5-hexatriene in plasma membranes of 20°C-acclimated trout was greater when determined in phosphate (AP per °C=-0.047) than in imidazole buffer (AP per °C=-0.022); similar, but less significant, trends were noted with 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene. In contrast, the temperature dependence of fluidity (AP/°C in the range-0.0222 to-0.027) did not vary with buffer composition in membranes of 5°C-acclimated trout. In phosphate buffer, anisotropy parameter values for 1,6-diphenyl-1,3,5-hexatriene were significantly lower in 5°C-than 20°C-acclimated trout, indicating a less restricted probe environment following cold acclimation and nearly perfect compensation (91%) of fluidity. Temperature-dependent patterns of acid-base regulation were estimated to account for 11–40% of the fluidization evident in membranes of 5°C-trout, but a period of cold acclimation was required for complete fluidity compensation. In contrast, no homeoviscous adaptation was evident in imidazole buffer, indicating that membrane fluidity is sensitive to buffer composition. Accordingly, vesicles of bovine brain phosphatidylcholine, suspensions of triolein, and plasma membranes of 5°C-acclimated trout were consistently more fluid in imidazole than phosphate buffer. Membranes of 5°C-acclimated trout were enriched in molecular species of phosphatidylcholine containing 22:6n3 (at the expense of species containing 18:1n9 and 18:2n6) compared to membranes of 20°C-trout; consequently, the unsaturation index was significantly higher (3.29 versus 2.73) in trout maintained at 5 as opposed to 20°C. It is concluded that: 1) the chemical composition of the internal milieu can significantly influence the physical properties of membrane lipids; 2) temperature-dependent patterns of intracellular pH regulation may partially offset the ordering effect of low temperature on membrane fluidity in 20°C-acclimated trout transferred to 5°C, but not in 5°C-acclimated trout transferred to warmer temperatures; 3) the majority of the thermal compensation of plasma membrane fluidity resulting from a period of temperature acclimation most likely reflects differences in membrane composition between acclimation groups; 4) imidazole apparently interacts with trout hepatocyte plasma membranes in a unique way.Abbreviations _im netcharge stateofproteins - AP anisotropyparameter - bw body weight - DPH 1,6-diphenyl-1,3,5-hexatriene - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonicacid - PC phosphatidylcholine - pH_e pHofarterial blood - pH_i intracellular pH - TMA-DPH 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene - TRIS tris(hydroxymethyl)aminomethane     

Effects of temperature and thermal history on neuromuscular properties of two crustacean species

Summary The effect of temperature on the ability of neuromuscular junctions and muscle fibers to contract, release neurotransmitter, and maintein postsynaptic membrane properties, was measured in vivo and in vitro in claw closer muscles in stone crabsMenippe mercenaria (Say) and blues crabsCallinectes sapidus (Rathbun).In vivo muscle stress (defined as force generated per unit of muscle cross-sectional area) was measured in crabs of both species collected from northern populations (annual temperature range 2–30°C) and southern populations (annual temperature range 15–30°C). Muscle stress was compared between (1) crabs of both species maintained in the laboratory at 30°C (laboratory warmed); (2) crabs given a brief acclimation period (4 weeks for blue crabs; 7 weeks for stone crabs) at 8°C in the laboratory (laboratory colled), and (3) stone crabs that had been naturally acclimated from summer (30°C) to winter (8°C) temperatures over a 6 month period in the field (naturally cooled). No differences were found in the abilities of the northern and southern populations of either species to generate muscle stress when tested at summer temperatures (30°C) common to both populations. Northern and southern blue crabs produced similar levels of muscle stress whether laboratory warmed (30°C) or laboratory cooled (8°C). Conversely, northern and southern stone crabs showed significantly reduced muscle stress in laboratory cooled crabs compared with laboratory warmed crabs. Stone crabs from both populations generated the same amount of muscle stress after having been naturally cooled to 8°C as they had generated the previous summer (30°C).In vitro neuromuscular properties (i.e. (1) muscle stress as a measure of contractile ability; (2) excitatory junction potential (EJP) amplitude as a measure of neurotransmitter release; (3) specific membrane resistance (R_m) as a measure of postsynaptic membrane properties) were compared at 8, 20, and 30°C between northern cold acclimated (naturally cooled stone crabs and laboratory cooled blue crabs) and non-cold acclimated (laboratory cooled stone crabs. Muscle fibers in claws of stone crabs and blue crabs showing cold acclimation had higher R_m at 8°C than non-cold acclimated crabs. This higher R_m resulted in a broadening of EJP's which enhanced EJP summation, muscle fiber depolarization, and muscle stress.Abbreviations EJP excitatory junction potential - E _r resting membrane potential - F _e lacilitation - R _m specific membrane resistance     

Effect of temperature and temperature acclimation on the ryanodine sensitivity of the trout myocardium

The influence of acute temperature change and temperature acclimation on the sensitivity of contracture development to ryanodine were examined in the rainbow trout myocardium using two preparations: in vitro isolated ventricular strips and in situ working perfused hearts. Ryanodine effects in vitro were dependent on test temperature (8 and 18 °C), pacing frequency (0.2–1.5 Hz) and acclimation temperature (8 and 18 °C). At a pacing frequency of 0.2 Hz and a test temperature of 18 °C, ryanodine depressed isometric tension development in ventricular strips both from trout acclimated to 8 and 18 °C but the decrease was significantly greater in strips from 8 °C-acclimated trout. No ryanodine effect was observed in either acclimation group at a test temperature of 8°C. The effect of ryanodine in vitro was reduced or lost at pacing frequencies greater than 0.2 Hz and at 0.6 Hz ryanodine depressed tension development at 18 °C only in strips from 8 °C-acclimated trout. Ryanodine did not affect tension development at stimulation rates above 0.6 Hz in any test group. Likewise, ryanodine did not significantly impair cardiac performance of in situ working perfused heart preparations which operated at intrinsic beat frequencies in excess of 0.6 Hz. These results suggest that the sarcoplamic reticulum calcium release channel of the trout myocardium is expressed but is not functionally involved in beat-to-beat regulation of contractility at either (1) low temperature (8 °C), or (2) at routine physiological heart rate (>0.6 Hz). However, under conditions in which involvement of the sarcoplasmic reticulum is observed (18 °C and a heart rate < 0.6 Hz), prior acclimation to low temperature results in either a greater capacity of the sarcoplasmic reticulum to store releasable calcium or an increase in the amount of calcium that is in releasable form.Abbreviations bm body mass - E-C coupling, excitation-contraction coupling - IVS isometric ventricular strip - SR sarcoplasmic reticulum - TES N-tris[hydroxy-methyl]methyl-2-aminoethane sulfonic acid - WPH in situ working perfused heart     

Incorporation of 1-14C-acetate into fatty acids and sterols by isolated hepatocytes of thermally acclimated rainbow trout (Salmo gairdneri)

Summary Rates of 1-¹⁴C-acetate incorporation into specific fatty acids and sterol fractions were determined at assay temperatures of 5°C and 20°C in hepatocytes isolated from warm (20°C)- and cold (5°C)- acclimated rainbow trout (Salmo gairdneri). Rates of sterol lipogenesis were 2.5- to 3-fold higher in hepatocytes from cold-acclimated trout. Rates of acetate oxidation and of total fatty acid lipogenesis did not differ significantly between acclimation groups. Fatty acid compositions did not change significantly during the experiment (9–12 h), but hepatocytes from cold-acclimated trout possessed significantly higher levels of polyunsaturates and unsaturates of the linolenic acid (n-3) family, and significantly lower levels of monounsaturates than did hepatocytes from warm-acclimated animals. Hepatocytes from cold-acclimated trout channeled a larger percentage of their total acetate incorporation into unsaturated fatty acids at 5°C than at 20°C due primarily to increased recovery of acetate in polyunsaturates and monoenes at 5°C. In contrast, hepatocytes from warm-acclimated trout channeled a slightly smaller percentage of their total acetate incorporation into unsaturates at 5°C than at 20°C. Hepatocytes from warm-acclimated trout incorporated significantly more 1-¹⁴C-acetate into the unsaturated fatty acid fraction (due primarily to incorporation into the diene fraction and less importantly all other classes of unsaturates) and significantly less into the saturated fatty acid fraction than hepatocytes from cold-acclimated trout when assayed at 20°C; similar but less dramatic differences were observed at 5°C. Consequently, unsaturated/saturated ratios for acetate incorporation ranked: warm-acclimated at 20°Cwarm-acclimated at 5°Ccold-acclimated at 5°C>cold-acclimated at 20°C. These results suggest that regulation of the relative rates of unsaturated and saturated fatty acid synthesis is involved in lipid restructuringduring adaptation from one temperature regime to another, but that other mechanisms must be invoked to explain the maintenance of observed steady state differences between the fatty acid compositions of warm- and cold-acclimated trout.This work was supported by grant PCM-76-04313-AO1 from the National Science Foundation     

Calcium regulatory proteins and temperature acclimation of actomyosin ATPase from a eurythermal teleost (Carassius auratus L.)

Summary Goldfish (Carassius auratus) were acclimated for 5 months at temperatures of either 2°C or 31°C. Natural actomyosin was prepared from white myotomal muscle and its Mg²⁺Ca²⁺ ATPase activity determined. Temperature acclimation results in adaptations in substrate turnover number and thermodynamic activation parameters of the ATPase. When assayed at 31°C the Mg²⁺Ca²⁺ ATPase of natural actomyosin was 4 times higher in 31°C than 2°C acclimated fish. Arrhenius plots of natural actomyosin ATPase from cold acclimated fish show a break in slope at 15–18°C. In contrast, the temperature dependence of warm acclimated actomyosin was linear. Activation enthalpy (H ) of the ATPase, calculated over the range 0–16°C, was approximately 8,000 cal/mole lower in 2°C than 32°C acclimated fish.In contrast, desensitised actomyosins from which the calcium regulatory proteins have been removed show a linear temperature dependence in the range 0–32°C and have similar properties in 2°C and 31°C acclimated fish. Cross-hybridisation of regulatory proteins (tropomyosin-troponins complex) from cold-acclimated fish to desensitised actomyosin from warm-acclimated fish alters the ATPase towards that of cold-acclimated natural actomyosin and vice versa. The results suggest that the regulatory proteins can influence the kinetics of the ATPase and, furthermore, that they are involved in the acclimation of the actomyosin to different cell temperatures.     

Interactive effects of season and temperature on enzyme activities,tissue and whole animal respiration in roach,Rutilus rutilus

Synopsis This paper reviews investigations on the ecophysiology of a population of roach, Rutilus rutilus, from a subalpine oligotrophic lake in the Austrian Tirol. Metabolic responses to season and temperature were studied in whole animals, tissues and selected enzymes. The exponent of the relationship between body mass and three levels of the metabolic rate of acclimated fish was 0.82 ± 0.02, 0.60 ± 0.15, and 0.75 ± 0.01 at 4, 12, and 20° C respectively. Various combinations of long-term acclimation to constant or seasonally fluctuating temperatures and long-term (up to 14 days) monitoring of O₂ at the acclimation temperature led to the conclusion that the aerobic power of fish swimming in the routine mode does not show any sign of being temperature compensated. On the other hand, there are several indications that the energy expenditure of spontaneously swimming fish is adjusted to the seasonal pattern of environmental change and that these responses of metabolism and behaviour are controlled by both endogenous and exogenous factors. The rate of oxygen consumption of gill and muscle tissue brei from fish caught during a seasonal cycle and measured at 15° C appears to follow closely the reproductive and gonadal cycle of the living fish. The same holds for the activities of phosphofructokinase, acetoacetyl-CoA thiolase, and cytochrome oxidase. On the other hand, the Na⁺, K⁺-ATPase of the kidney shows near perfect temperature compensation when fish acclimated to 5 and 25° C are compared, whereas an equally pronounced case of inverse temperature acclimation has been reported for the activity of digestive enzymes in the gut. Summarizing these data it is pointed out that the temperature relationship of a poikilothermic organism is the sum of often very diverse temperature relationships of specific metabolic and behavioural functions. In the case of the roach, strong effects of acclimation temperature on the molecular level, sometimes in the opposite direction, combine with seasonal effects on enzyme activities and tissue respiration. However, on the whole animal level the fish behave as strictly non-compensating poikilotherms, the reproductive cycle being the only detectable influence capable of modulating the basic temperature relationship of energy expenditure.     

Effect of constant and fluctuating temperatures on resting and active oxygen consumption of toads,Bufo boreas

Summary The relations of standard and active rates of oxygen consumption to body temperature (T_b) were tested in montane Bufo b. boreas and lowland Bufo boreas halophilus acclimated to constant T _b of 10, 20, or 30° C or to a fluctuating cycle of 5–30° C. Standard metabolic rates (SMR) of boreas acclimated to 30° C and halophilus acclimated to 10° C show pronounced regions of thermal independence but all other standard and active metabolic rates of groups acclimated to other thermal regimes are thermally sensitive. The SMR of both subspecies acclimated to the 5–30° C cycle are more thermally sensitive than those of similar individuals acclimated to constant T _b. In cases where the relation between SMR and T _b is linear for both halophilus and boreas at the same acclimation temperature, the slope and Q₁₀ of the relation for boreas are significantly higher than those of halophilus. Acclimation had little or no effect on the active metabolic rates of either subspecies. The relation between SMR and T _b of boreas maintained under field conditions (Carey, 1979) is matched only by those of individuals from the same population acclimated to 20° C.     

The effects of assay temperature upon the pH optima of enzymes from poikilotherms: A test of the imidazole alphastat hypothesis

Summary A study of the thermal responses of Na-ATPase and NaK-ATPase activities in microsomes prepared from gill tissue of rainbow trout (Salmo gairdneri) revealed further evidence that the two activities are distinct from one another. Arrhenius plots of the NaK-ATPase from sea water-adapted fish and the Na-ATPase from fresh water-adapted fish were linear (Fig. 4) with estimated activation energies of 19.5 and 7.7 kcal/mole, respectively. The Na-ATPase and NaK-ATPase both showed optimum activity at 45°C (Figs. 2 and 3). The Mg-ATPase from fresh water fish showed a distinct temperature optimum at 24°C (Fig. 1) while Mg-ATPase activity from sea water fish was optimum at temperatures of about 15–24 °C (Fig. 3). The Na⁺ dependence of the Na-ATPase and the NaK-ATPase was examined at an assay temperature of 37 °C (Fig. 5) and the results compared with those obtained at 13 °C. No apparent differences were noted for the Na-ATPase, but with the NaK-ATPase both theK _0.5 for Na⁺ and optimum Na⁺ concentration increased at the higher assay temperature. Finally, evidence is presented showing the Na-ATPase to be distinct from Mg-ATPase activity in fresh water trout gill microsomes.Abbreviation HEPES N-2-hydroxyethylpiperazine-N-2-ethane-sulfonic acid     

Temperature acclimation in brook trout muscle: Adenine nucleotide concentrations, phosphorylation state and adenylate energy charge

Summary Cold acclimation in fish is associated with an elevation in metabolic rate. The present study investigates the role of adenine nucleotides and related compounds in metabolic regulation following temperature acclimation. Brook trout (Salvelinus fontinalis) were acclimated for 10 weeks to either +4°C or +24°C. Both groups of fish were exercised at 2.5 body lengths s^–1 for 2 weeks prior to sacrifice in order to control for differences in spontaneous activity.Concentrations of ATP, ADP, AMP, P _i and PC were approximately 2-fold higher in white than red muscles. Temperature acclimation had little effect on total adenine nucleotide concentration in either muscle type. In white fibres acclimation to 4°C results in a 39% increase in [ADP] and [AMP], a 35% decrease in [PC] (phosphorylcreatine), and no significant change in [P _i ]. In contrast temperature has little effect on concentrations of these compounds in red muscle.Parameters of metabolic control — adenylate energy charge ([ATP]+0.5 [ADP]/[ATP]+[ADP]+[AMP]), phosphorylation state ([ATP]/[ADP]·[P _i ]), and the ratios [ATP][ADP] and [ATP][AMP] — were significantly lower in cold- than warm-acclimated white muscle. The observed changes in phosphorylation state and [ATP][AMP] are consistent with an increase in mitochondrial respiration and glycolysis, respectively.In conclusion, changes in metabolites may be an important factor in producing an enhanced metabolic rate in cold-acclimated fish.     

Photosynthetic responses of Arctic sea-ice microalgae to short-term temperature acclimation

Summary In April-May 1986, sea-ice microalgae (southcastern Hudson Bay, Canadian Arctic) were acclimated to temperatures ranging from-1.5° to 10°C for short periods (3 h), after which photosynthesis and carboxylating enzyme activities were measured. P _max ^b increased after acclimation to 10°C while photosynthetic parameters , and I_k as well as activities of PePC and PePCk did not show any significant change after temperature acclimation. Contrary to P _max ^b , the activity of RuBPC was lower for algae acclimated to 3°-10°C, the observed response increasing with temperature. There was also a seasonal trend in the response of RuBPC, the ability to compensate for rapid temperature changes being higher in May. These results show that ice algae were photosynthetically adaptable in the range of temperatures tested. For RuBPC, adaptability developed seasonally when the environmental temperature started to fluctuate in May. Photosynthetic acclimatization to temperature may be of high ecological significance in extending the growth season of ice-algae.Contribution to the programs of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Maurice-Lamontagne Institute (Department of Fisheries and Oceans)     

Heat Resistance and Thermal Acclimation Rate in Tropical Tetra <Emphasis Type="Italic">Astyanax bimaculatus</Emphasis> of Venezuela

Venezuelan river tetra, Astyanax bimaculatus juveniles of 34.1–36.7mm standard length and 0.83–1.0g wet weight were acclimated for four weeks to 24–33°C, which are approximate average minimum and maximum river temperatures throughout the year. The fish acclimated to 24, 27, 30, and 33°C were exposed for 10000 minutes at 35, 36, 37, 38, and 39°C to determine individual heat resistance times. To determine acclimation rates, the juveniles acclimated to 24 and 30°C were tested for individual heat resistance times at 39°C by changing acclimation temperatures. The individual heat resistance times were increased in accordance with an increase in acclimation temperature and a decrease in test temperature, indicating that acclimation level has a great influence on thermal resistance of the fish tested. As the fish were transferred from 24 to 30°C (upward acclimation), they completed their acclimation level in a few days, while those transferred from 30 to 24°C (downward acclimation) required about 14 days. It has reaffirmed the following general behavior: the rate of gain in thermal resistance is fast and the loss in heat tolerance is very slow. This physiological phenomenon is very important for tropical fish, which acclimates rapidly in rising temperature during the hot day and does not lose this level in decreasing temperature during the cool night. Consequently, a tropical fish can maintain its maximum resistance level, adapt well in thermally fluctuating tropical waters, and survive in lethally high temperatures caused by a sudden increase in temperature during hot day.     

Heat production in cold and long scotophase acclimated and winter acclimatized rodents

Heat production by means of oxygen consumptionVo₂ (at T_a = 6° C, 25° C, 30° C, and 32° C) and non-shivering thermogenesis (NST) were studied in individuals of a diurnal rodent (Rhabdomys pumilio) and a nocturnal rodent (Praomys natalensis). The studied mice were acclimated to cold at T_a=8°C with a photoperiod of LD 12:12. On the otherhand specimens of these two species were acclimated at T_a=25°C with a long scotophase LD8:16. The results were compared with a control group (T_a=25° C, LD 12:12) and winter acclimatized individuals of both species.Vo₂ in cold acclimated mice of both species was significantly increased when compared to the control group and was even higher than the winter acclimatized group when measured below the lower critical temperature. Long scotophase acclimated mice of both species also increased their oxygen consumption significantly when compared to the control group. NST was significantly increased in long scotophase acclimated mice from both species when compared to the control group. The results of this study indicate that the effects of acclimation to long scotophase are similar to those of cold acclimation. As changes in photoperiod are regular, it may be assumed that heat production mechanisms in acclimatization to winter will respond to changes in photoperiodicity.Present address: University of Haifa, Oranim, P.O. Kiryat Tivon, Israel.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Effects of acclimation and acute temperature change on specific dynamic action and gastric processing in the green shore crab, Carcinus maenas

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10 °C or 20 °C and subsequently exposed to treatment temperatures of 5, 15, or 25 °C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10 °C acclimated group exposed to acute test temperatures. The Q₁₀ values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20 °C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20 °C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20 °C acclimated crabs, with the highest value measured at the treatment temperature of 15 °C. The decline in total SDA after acute exposure to 5 and 25 °C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20 °C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10 °C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones.     

Thermal sensitivity of white muscle lactate dehydrogenase isolated from a lake trout, (<Emphasis Type="Italic">Salmo trutta</Emphasis>), inhabiting lake Plav,Montenegro

To shed light on thermoadaptive properties of Salmo trutta from lake Plav (Montenegro), we undertook kinetic studies of pyruvate reduction rates and thermal stability analyses of white muscle LDH. We compared these with the data obtained for trout of the same, confirmed by us, Danubian lineage living in rivers and streams of Serbia and Montenegro. We also tested the effect of acclimation in captivity at 4 and 14 °C. The lake trout was of a typical smoltified phenotype (the size, the elongated silver colored body). At physiological substrate concentration, the breaks in the Arrhenius plots (critical temperature - T_c) correlated with acclimation temperatures or habitat water temperatures. Q₁₀ values for temperatures above T_c were close to one, in all cases except 4 °C acclimated trout. At temperatures below T_c Q₁₀ was close to two, except in the case of 14 °C acclimated trout. Lake trout had a highest Q₁₀ values at temperatures below T_c. It was conspicuous that within the entire range of tested temperatures the differences in Q₁₀ resulted from the effect of environmental temperature. Higher Q₁₀ values were obtained with LDH isolated from trout acclimated to 4 °C compared with LDH acclimated to 14 °C. E_a values were much lower at a temperature below T_c compared with temperatures above Tc. Thermal stability of muscle LDH was lower after acclimation to 14 compared to 4 °C, while extremely high thermostability was obtained with the lake trout enzyme. Our data support the concept that T_c values have distinct physiological significance.     

Aerobic mitochondrial capacities in Antarctic and temperate eelpout (Zoarcidae) subjected to warm versus cold acclimation

Capacities and effects of cold or warm acclimation were investigated in two zoarcid species from the North Sea (Zoarces viviparus) and the Antarctic (Pachycara brachycephalum) by investigating temperature dependent mitochondrial respiration and activities of citrate synthase (CS) and NADP⁺ -dependent isocitrate dehydrogenase (IDH) in the liver. Antarctic eelpout were acclimated to 5°C and 0°C (controls) for at least 10 months, whereas boreal eelpout, Z. viviparus (North Sea) were acclimated to 5°C and to 10°C (controls). Liver sizes were found to be increased in both species in the cold, with a concomitant rise in liver mitochondrial protein content. As a result, total liver state III rates were elevated in both cold-versus and warm-exposed P. brachycephalum and Z. viviparus, with the highest rates in boreal eelpout acclimated to 5°C. CS and IDH activities in the total liver were similar in Z. viviparus acclimated to 5°C and 10°C, but decreased in those warm acclimated versus control P. brachycephalum. Enzyme capacities in the total liver were higher in eelpout from Antarctica than those from the North Sea. In conclusion, cold compensation of aerobic capacities in the liver seems to be linked to an increase in organ size with unchanged specific mitochondrial protein content. Despite its life in permanently cold climate, P. brachycephalum was able to reduce liver aerobic capacities in warm climate and thus, displayed a capacity for temperature acclimation.     

Respiration of juvenile Arctic cod (Boreogadus saida): effects of acclimation,temperature, and food intake

Oxygen consumption (VO₂) of juvenile Arctic cod (Boreogadus saida) was investigated at low tempera tures (six temperatures; range -0.5 to 2.7°C). Small (mean wt. 6–8 g) and large (mean wt. 14 g) fish were acclimated, or adjusted to a constant temperature (0.4°C), for 5 months and then tested for metabolic cold adaptation (elevated metabolic rates in polar fishes). Short-term (2 weeks) acclimated fish showed elevated VO₂ similar to previously established values for polar fishes, but there was no such evidence after longterm acclimation. Long-term acclimation caused VO₂ values to drop significantly (from 86.0 to 46.5 mg O₂·kg^–1·h^–1, at 0.4°C), which showed that metabolic cold adaptation was a phenomenon caused by insufficien: acclimation time for fish in respiration experiments. We also measured the effects of temperature and feeding on VO₂. A temperature increase of 2.3°C resulted in relatively large increases in VO₂ for both longand short-term acclimated fish (Q₁₀ = 6.7 and 7.1, respectively), which suggests that metabolic processes are strongly influenced by temperature when it is close to zero. Feeding individuals to satiation caused significant increases in VO₂ above pre-fed values (34–60% within 1–2 days after feeding). Respiration budgets of starved and fed Arctic cod at ambient temperatures in Resolute Bay N.W.T., Canada, were used to model annual respiration costs and potential weight loss. Low respiration costs for Arctic cod at ambient temperatures result in high growth efficiency during periods of feeding and low weight loss during periods of starvation.     

Effects of temperature and CO2 enrichment on kinetic properties of phospho-enol-pyruvate carboxylase in two ecotypes of Echinochloa crus-galli (L.) Beauv., a C4 weed grass species

Summary Two populations of Echinochloa crus-galli (Québec, Mississippi) were grown at the Duke University Phytotron under 2 thermoperiods (28°/22°C, 21°/15°C day/night) and 2 CO₂ regimes (350 and 675 l l^-1). Thermostability, energy of activation (E _a ),K _m (PEP), K _m (Mg⁺⁺), and specific activity of phospho-enol-pyruvate carboxylase (PEP_c) were analyzed in partially purified enzyme preparations of plants grown for 5 weeks. Thermostability of PEP_c from extracts (in vitro) and leaves (in situ) was significantly higher in Mississippi plants. In vitro denaturation was not appreciably modified by thermal acclimation but CO₂ enrichment elicited higher thermostability of PEP_c. In situ thermostability was significantly higher than that of in vitro assays and was higher in Mississippi plants acclimated at 28°/22°C and in plants of the two ecotypes grown at 675 l l^-1 CO₂. E _a (Q ₁₀ 30°/20°C) for PEP_c was significantly lower in Québec plants as compared to Mississippi and no acclimatory shifts were observed. Significantly higher K _m's (PEP) in 20°C assays were obtained for Mississippi as compared to Québec plants but values were similar at 30°C and 40°C assays. K _m (Mg⁺⁺) decreased at higher assay temperatures and were significantly lower for PEP_c of the Québec ecotype. No significant changes in K _m (Mg⁺⁺) values were associated with modifications in temperature on CO₂ regimes. PEP_c activity measured at 30°C was significantly higher for Québec plants when measured on a leaf fresh weight, leaf area or protein basis but not on a chlorophyll basis. Significantly higher PEP_c activity for both genotypes was observed for plants acclimated at 21°/15°C or grown at 675 l l^-1 CO₂. Net photosynthesis (Ps) and net assimilation rates (NAR) were higher in Québec plants and were enhanced by CO₂ enrichment. NAR was higher in plants acclimated at low temperature, while an opposite trend was observed for Ps. PEP_c activities were always in excess of the amounts required to support observed rates of CO₂ assimilation.     

Sub-lethal temperature thresholds indicate acclimation and physiological limits in brook trout Salvelinus fontinalis

The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CT_max) experiments on fish acclimated to temperatures that span the species' thermal range (5–25°C). The CT_max increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato-somatic index (I_H) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub-lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance.