Temperature acclimation and oxygen binding properties of blood of the European eel, Anguilla anguilla

Temperature acclimation of the European eel, Anguilla anguilla, resulted in red cell GTP/Hb molar ratios of 1.20, 1.77 and 0.80 at 2, 17 and 29 degrees C, respectively. A small increase in blood oxygen capacity was present in 29 degrees C acclimated eels. The CO2 Bohr effect and the shape of the oxygen binding curve (n-Hill) were invariant with both temperature and GTP/Hb. The significant differences in the GTP/Hb ratio corresponded with a strong enhancement of the temperature effect on blood oxygen affinity between 2 and 17 degrees C and a similarly strong compensation between 17 and 29 degrees C. Predicted in vivo P50 values were 3.0, 13.8 and 17.6 mmHg at 2 degrees C, 17 and 29 degrees C, respectively. The adaptational value of these findings are discussed in relation to standard metabolic rates at the various temperatures. A tentative hypothesis is proposed that the present study confirms and expands earlier work and supports the contention that adjustments in blood oxygen affinity of thermally acclimated teleosts serve to provide them with an unloading O2 tension for diffusion closely matching the standard oxygen requirements at the various temperatures.     

Physiological effects of dietary cadmium acclimation and waterborne cadmium challenge in rainbow trout: respiratory, ionoregulatory, and stress parameters

A suite of respiratory, acid-base, ionoregulatory, hematological, and stress parameters were examined in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 45 days and during a subsequent challenge to waterborne Cd (10 microg/L) for 72 h. Blood sampling via an indwelling arterial catheter revealed that dietary Cd had no major effects on blood gases, acid-base balance, and plasma ions (Ca(2+), Mg(2+), K(+), Na(+), and Cl(-)) in trout. The most notable effects were an increase in hematocrit (49%) and hemoglobin (74%), and a decrease in the plasma total ammonia (43%) and glucose (49%) of the dietary Cd-exposed fish relative to the nonexposed controls. Dietary Cd resulted in a 26-fold increase of plasma Cd level over 45 days (approximately 24 ng/mL). The fish exposed to dietary Cd showed acclimation with increased protection against the effects of waterborne Cd on arterial blood P(aCO2) and pH, plasma ions, and stress indices. After waterborne Cd challenge, nonacclimated fish, but not Cd-acclimated fish, exhibited respiratory acidosis. Plasma Ca(2+) levels declined from the prechallenge level, but the effect was more pronounced in nonacclimated fish (44%) than in Cd-acclimated fish (14%) by 72 h. Plasma K(+) was elevated only in the nonacclimated fish. Similarly, waterborne Cd caused an elevation of all four traditional stress parameters (plasma total ammonia, cortisol, glucose, and lactate) only in the nonacclimated fish. Thus, chronic exposure to dietary Cd protects rainbow trout against physiological stress caused by waterborne Cd and both dietary and waterborne Cd should be considered in determining the extent of Cd toxicity to fish.     

Hypohydration and exercise: effects of heat acclimation, gender, and environment

This study examined the effects of heat acclimation and subject gender on treadmill exercise in comfortable (20 degrees C, 40% rh), hot-dry (49 degrees C, 20% rh), and hot-wet (35 degrees C, 79% rh) environments while subjects were hypo- or euhydrated. Six male and six female subjects, matched for maximal aerobic power and percent body fat, completed two exercise tests in each environment both before and after a 10-day heat acclimation program. One exercise test was completed during euhydration and one during hypohydration (-5.0% from baseline body weight). In general, no significant (P greater than 0.05) differences were noted between men and women at the completion of exercise for rectal temperature (Tre), mean skin temperature (Tsk), or heat rate (HR) during any of the experimental conditions. Hypohydration generally increased Tre and HR values and decreased sweat rate values while not altering Tsk values. In the hypohydration experiments, heat acclimation significantly reduced Tre (0.19 degrees C) and HR (13 beats X min-1) values in the comfortable environment, but only HR values were reduced in hot-dry (21 beats X min-1) and hot-wet (21 beats X min-1) environments. The present findings indicated that men and women respond in a physiologically similar manner to hypohydration during exercise. They also indicated that for hypohydrated subjects heat acclimation decreased thermoregulatory and cardiovascular strain in a comfortable environment, but only cardiovascular strain decreased in hot environments.     

Regulation of expression of two aquaporin homologs in the intestine of the European eel: effects of seawater acclimation and cortisol treatment

Complementary DNAs encoding homologs of the mammalian aquaglyceroporins (termed AQPe) and aquaporin-1 isoforms (termed AQP1) were isolated from the European eel. The AQP amino acid sequences share 35-54% identity with other known human AQPs. Although AQPe mRNA expression was approximately equivalent along the entire length of the gut, AQP1 expression was the highest in the posterior/rectal segment. Seawater (SW) acclimation increased AQP1 mRNA abundance by 5- and 17-fold in the anterior, 14- and 23-fold in the mid-, and 9- and 7-fold in the posterior/rectal gut regions of yellow and silver eels, respectively. SW acclimation had an effect on AQPe mRNA expression only in the midintestine of silver eels, where a small but significant 1.7-fold increase in abundance was measured. Western blots using an eel AQP1-specific antibody identified the presence of a major immunoreactive 28-kDa protein, primarily within the posterior/rectal segment. A 3-wk SW transfer induced an increase in AQP1 protein abundance in all intestinal segments, with the posterior/rectal region still expressing protein levels approximately 40- and 8-fold higher than the anterior and midsegments, respectively. Strong AQP1 immunofluorescence was detected within the vascular endothelium in both freshwater (FW)- and SW-acclimated eels and in the epithelial apical brush border in the posterior/rectal gut regions of SW-acclimated eels. Cortisol infusion into FW eels had no effect on intestinal AQPe mRNA expression but induced increases in AQP1 mRNA and protein levels. These results provide evidence for the presence of a SW-induced and steroid-regulated AQP water channel pathway within the intestine of the European eel.     

Phosphite disrupts the acclimation of Saccharomyces cerevisiae to phosphate starvation.

The influence of phosphite (H2PO3-) on the response of Saccharomyces cerevisiae to orthophosphate (HPO4(2-); Pi) starvation was assessed. Phosphate-repressible acid phosphatase (rAPase) derepression and cell development were abolished when phosphate-sufficient (+Pi) yeast were subcultured into phosphate-deficient (-Pi) media containing 0.1 mM phosphite. By contrast, treatment with 0.1 mM phosphite exerted no influence on rAPase activity or growth of +Pi cells. 31P NMR spectroscopy revealed that phosphite is assimilated and concentrated by yeast cultured with 0.1 mM phosphite, and that the levels of sugar phosphates, pyrophosphate, and particularly polyphosphate were significantly reduced in the phosphite-treated -Pi cells. Examination of phosphite's effects on two PHO regulon mutants that constitutively express rAPase indicated that (i) a potential target for phosphite's action in -Pi yeast is Pho84 (plasmalemma high-affinity Pi transporter and component of a putative phosphate sensor-complex), and that (ii) an additional mechanism exists to control rAPase expression that is independent of Pho85 (cyclin-dependent protein kinase). Marked accumulation of polyphosphate in the delta pho85 mutant suggested that Pho85 contributes to the control of polyphosphate metabolism. Results are consistent with the hypothesis that phosphite obstructs the signaling pathway by which S. cerevisiae perceives and responds to phosphate deprivation at the molecular level.     

Changes in haemoglobin binding curve and oxygen transport in chronic hypoxic lung disease.

Direct measurements of the factors determining blood oxygen transport in 10 patients with chronic hypoxic respiratory failure led to the conclusion that wide differences in the position of their oxygen binding curves, due to spontaneous differences in red-cell 2, 3-diphosphoglycerate, had little effect on oxygen delivery to the tissues, as assessed by the mixed venous oxygen tension when they were breathing air. This result arises from the shape of the oxygen binding curve. A drug which could shift the curve to the right would help tissue oxygenation in cardiogenic and other forms of shock, when a low cardiac output can not be improved though arterial blood can be well oxygenated.     

The effects of starvation and temperature acclimation on pentose phosphate pathway dehydrogenases in brook trout liver

Temperature and starvation were found to be factors which affected the PPP dehydrogenase activities in brook trout liver. Fish acclimated at 5 °C possessed greater levels of G6PD, H6PD, and 6PGD activity than those fish maintained at 10 or 15 °C. This phenomenon was probably associated with increased lipogenesis during cold acclimation.During starvation hepatic G6PD and 6PGD activities decreased, whereas H6PD activity increased slightly. Upon refeeding, the G6PD level gradually increased, but the “overshoot” in enzyme activity reported in mammalian studies was not observed.When both cold acclimation and starvation were studied simultaneously, regulation by temperature was initially the dominant control factor. After 6 wk at 5 °C, there was no difference in specific activities between starved and fed fish. However, fish maintained at 5 °C for longer than 2 mo did show the normal response to starvation and refeeding. Therefore, regulation of the PPP by temperature appears to be a transitory phenomenon and may be associated with temporary metabolic reorganization in the fish.     

Chemical properties of the N-termini of human haemoglobin.

The chemical properties, namely pK and reactivity, of the N-termini of oxyhaemoglobin and deoxyhaemoglobin toward acetic anhydride and 1-fluoro-2,4-dinitrobenzene (Dnp-F) were determined by the competitive-labelling approach [Kaplan, Stevenson & Hartley, (1971) Biochem. J. 124, 289-229; Duggleby & Kaplan (1975) Biochemistry 14, 5168-5175]. At physiological pH and temperature, the valine-1 alpha and valine-1-beta amino groups had unusually low pK values, but showed only minimal changes in their pK values on deoxygenation. Between pH 7.5 and pH 8.0 a deviation was observed in the pH-reactivity profiles and the apparent pK values became markedly pH-dependent. It was found that Dnp-F, but not acetic anhydride, had an abnormally high reactivity toward the N-termini. It is concluded that the valine-1 alpha and valine-1 beta N-termini make little or no contribution to the alkaline Bohr effect at physiological pH values. The high reactivity toward Dnp-F is attributed to an interaction or binding near the N-terminal region, and the discontinuity in the pH-reactivity profile at moderate alkaline pH values to a conformational change which alters the environment of these groups.     

Effects of assay and acclimation temperatures on incorporation of amino acids into protein of isolated hepatocytes from the european eel, L.

Hepatocytes of adult eels acclimated to 5° C, 10° C and 20° C, respectively were isolated by perfusion of the liver with collagenase. The liver-somatic index and the protein content of liver cells showed significantly higher values in fish kept at the lower temperatures. However, in the adenine nucleotide content and energy charge no significant differences were observed between the 5° C and the 20° C acclimation groups. The incorporation of radioactivity from a ¹⁴C-labelled amino acid mixture into perchloric acid precipitates was used as an estimate of over-all protein synthesis. When eel hepatocytes were incubated in Hanks' solution containing tracer amounts of amino acids, labelling of perchloric acid precipitates showed linear time courses over at least 60 min at 10° C and 20° C assay temperatures. The total cellular radioactivity, however, exhibited non-linear time courses. In the measurement range from 5° C to 25° C Arrhenius plots of protein labelling exhibited a discontinuity in both groups of fish. Hepatocytes from 10° C-acclimated eel showed almost twice the incorporation rates of amino acids as those from the 20° C-acclimated fish. It is concluded that high temperature dependencies in the low temperature range require an increase in the capacity of the apparatus for protein synthesis during cold acclimation.     

Glass eel (Anguilla anguilla) acclimation to freshwater and seawater: morphological changes of the digestive tract

Glass eels ( Anguilla anguilla , L. 1758) caught during ascent at the mouth of the River Tiber were kept in aquaria with freshwater and full strength salinity (35 %) for four months.
Morphological features of glass eels at capture and after four months of experimental rearin are described. The structure of the gut, an important osmoregulatory organ, observed in glass eels in seawater experimental rearing suggests that they undergo an irreversible process of adaptation to freshwater, despite the fact of survival in seawater.     

Physiological acclimation dampens initial effects of elevated temperature and atmospheric CO2 concentration in mature boreal Norway spruce

Physiological processes of terrestrial plants regulate the land–atmosphere exchange of carbon, water, and energy, yet few studies have explored the acclimation responses of mature boreal conifer trees to climate change. Here we explored the acclimation responses of photosynthesis, respiration, and stomatal conductance to elevated temperature and/or CO₂ concentration ([CO₂]) in a 3‐year field experiment with mature boreal Norway spruce. We found that elevated [CO₂] decreased photosynthetic carboxylation capacity (?23% at 25 °C) and increased shoot respiration (+64% at 15 °C), while warming had no significant effects. Shoot respiration, but not photosynthetic capacity, exhibited seasonal acclimation. Stomatal conductance at light saturation and a vapour pressure deficit of 1 kPa was unaffected by elevated [CO₂] but significantly decreased (?27%) by warming, and the ratio of intercellular to ambient [CO₂] was enhanced (+17%) by elevated [CO₂] and decreased (?12%) by warming. Many of these responses differ from those typically observed in temperate tree species. Our results show that long‐term physiological acclimation dampens the initial stimulation of plant net carbon assimilation to elevated [CO₂], and of plant water use to warming. Models that do not account for these responses may thus overestimate the impacts of climate change on future boreal vegetation–atmosphere interactions.     

Physiological acclimation of two psammophytes to repeated soil drought and rewatering

To understand physiological acclimation of psammophyte to repeated soil drought and rewatering, two psammophytes (Setaria viridis and Digitaria ciliaris) were subjected to three cycles of soil drought and rewatering. The response process of leaf relative water content (RWC), membrane permeability, lipid peroxidation, gas exchange characteristics, antioxidant enzymes, soluble protein, and free proline was examined. Leaf RWC, the net photosynthesis rate, stomatal conductance, and water use efficiency decreased, while membrane permeability, lipid peroxidation, intercellular CO₂ concentration, soluble protein, and free proline increased during three soil drought periods for both psammophytes. These physiological characteristics were recovered to the control levels following rewatering for 4 days. However, activities of SOD, CAT, and POD were induced continuously under soil drought conditions, and remained higher than those in the control throughout the whole experiment period, which agrees with our hypothesis that drought hardening activates defensive systems of both psammophytes continuously. Decreasing level of leaf RWC and increasing levels of leaf membrane permeability and lipid peroxidation were suppressed with increasing the number of drought cycles, suggesting that drought hardening alleviates damages of both psammophytes and improves their drought tolerance and acclimation to soil drought conditions in the future. Additionally, the photosynthesis decreased more slowly in the subsequent drought cycles than in the first cycle, allowing both psammophytes to maximize assimilation in response to repeated soil drought conditions. Thus, both psammophytes acclimatize themselves to repeated soil drought.     

Glutaminase in neurons and astrocytes cultured from mouse brain: Kinetic properties and effects of phosphate,glutamate, and ammonia

Phosphate activated glutaminase comprises two kinetically distinguishable enzyme forms in cultures of cerebellar granule cells, of cortical neurons and of astrocytes. Specific activity of glutaminase is higher in cultured neurons compared with astrocytes. Glutaminase is activated by phosphate in all cell types investigated, however, glutaminase in astrocytes reguires a much higher concentration of phosphate for half maximal activation. One of the products, glutamate, inhibits the enzyme strongly, whereas the other product ammonia has only a slight inhibitory action on the enzyme.