The development of endothermy during pouch life in the eastern barred bandicoot (Perameles gunnii), a marsupial

Marsupials are born ectothermic and gradually become endothermic during pouch occupancy. In order to study the timing of this transition, we measured the metabolic rates of eight pouch-young eastern barred bandicoots (Perameles gunnii) at 25 degrees C (the thermoneutral zone of adults), at 35 degrees C (pouch temperature), and after injection with norepinephrine. From 5 to 7 wk of age, oxygen consumption (VO(2)) was higher at 35 degrees C than at 25 degrees C. At 8 wk, VO(2) was significantly higher at 25 degrees C than at 35 degrees C. Norepinephrine administration at 5 and 6 wk had no effect on metabolic rate, but at 8 wk, near pouch vacation, it resulted in a significant increase in metabolic rate. Our results indicate that signs of thermoregulation for P. gunnii begin at 7 wk, and at 8 wk the species is endothermic, that is, able to increase heat production in response to both cold and norepinephrine. The appearance of fur, first seen at the age of 6 wk and fully developed at 8 wk, coincides with the onset of endothermy.     

High-altitude respiration of falconiformes. The primary structures and functional properties of the major and minor hemoglobin components of the adult White-Headed Vulture (Trigonoceps occipitalis, Aegypiinae)

The primary structures of the hemoglobin components Hb A and Hb D of White-Headed Vulture (Trigonoceps occipitalis) are presented. The globin chains were separated on CM-Cellulose in 8M urea buffer, the components by FPLC in phosphate buffers. The amino-acid sequences were established by automatic Edman degradation of the globin chains and of the tryptic peptides in liquid phase and gas-phase sequenators. The sequences differ from those of European Black Vulture by only one mutation in the alpha A-chains (alpha 137). The alpha D-chains and the beta-chains are identical. This means that for the first time identical minor components in birds have been found. An updated list of identical globin chains is presented. Hb D exhibited a higher oxygen affinity than Hb A. At pH 7.5 and 38 degrees C P50 values of 0.80 and 0.64 kPa (6.0 and 4.8 mm Hg), respectively. Both hemoglobins showed similar Bohr factors displayed a pronounced sensitivity to inositol hexakis(phosphate), which increased P50 values of Hbs A and D to 4.0 and 3.6 kPa (30 and 26 mm Hg), respectively. The molecular and physiological significance of the findings is discussed with special reference to oxygen transport by hemoglobin at high altitude.     

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.     

Oxygen affinity and amino acid sequence of myoglobins from endothermic and ectothermic fish

Myoglobin (Mb) buffers intracellular O2 and facilitates diffusion of O2 through the cell. These functions of Mb will be most effective when intracellular PO2 is near the partial pressure of oxygen at which Mb is half saturated (P50) of the molecule. We test the hypothesis that Mb oxygen affinity has evolved such that it is conserved when adjusted for body temperature among closely related animals. We measure oxygen P50s tonometrically and oxygen dissociation rate constants with stopped flow and generate amino acid sequence from cDNA of Mbs from fish with different body temperatures. P50s for the endothermic bluefin tuna, skipjack tuna, and blue marlin at 20 degrees C were 0.62 +/- 0.02, 0.59 +/- 0.01, 0.58 +/- 0.04 mmHg, respectively, and were significantly lower than those for ectothermic bonito (1.03 +/- 0.07 mmHg) and mackerel (1.39 +/- 0.03 mmHg). Because the oxygen affinity of Mb decreases with increasing temperature, the above differences in oxygen affinity between endothermic and ectothermic fish are reduced when adjusted for the in vivo muscle temperature of the animal. Oxygen dissociation rate constants at 20 degrees C for the endothermic species ranged from 34.1 to 49.3 s(-1), whereas those for mackerel and bonito were 102 and 62 s(-1), respectively. Correlated with the low oxygen affinity and fast dissociation kinetics of mackerel Mb is a substitution of alanine for proline that would likely result in a more flexible mackerel protein.     

Self-association of haemoglobin Olympia (alpha 2 beta 2 20 (B2) Val----Met). A human haemoglobin bearing a substitution at the surface of the molecule

Oxygenation measurements at equilibrium were carried out for solutions of pure haemoglobin (Hb) Olympia (alpha 2 beta 2 20 (B2) Val----Met) at 200 microM (haem) and revealed a high oxygen affinity (P50 = 4.2 torr at pH 7.20, 25 degrees C) compared to HbA (P50 = 5.6 torr), with the Hill coefficient (eta H) reduced from the normal value of 2.9 to 2.5 for Hb Olympia at neutral pH. 2,3-Diphosphoglycerate and chloride effects were normal, but measurements of the alkaline Bohr effect indicated an excess Bohr effect of about 20% for Hb Olympia. Precise determinations of the oxygen binding curves gave the unexpected finding of a dependence of co-operativity on pH with eta H rising from 2.4 at pH 6.8 to 3.0 at pH 8. Moreover, the Hill coefficient was dependent upon the concentration at alkaline pH and fell to 1.8 in low concentration solutions (approximately 30 microM-haem) of the haemoglobin variant; at this concentration the Bohr effect was normal. This effect of concentration on co-operativity could be accounted for fully by the allosteric model, with introduction of Hb Olympia self-association. In this case the allosteric constant L' for the supramolecular species has the value of the allosteric constant L for the tetramer species, raised to a power equal to the number of molecules in the aggregates and modulated by the ratio of the dissociation constants of the aggregates, DNR/DNT. Model curves with N tetramers per aggregate (where N approximately 2 at pH 7.5 and N approximately 4 at pH 8.0) fully represented the concentration dependence for Hb Olympia of the eta H values and the detailed shape of the experimental curves for eta H as a function of log[y/(1-y)], the first derivative of the Hill plot. These curves are much steeper when supramolecular species are present. Direct measurements of the protein aggregation by centrifugation confirmed the presence of aggregates in the solutions of Hb Olympia. Hb Olympia is therefore one of the few examples of mutant human haemoglobins that self-associate with functional consequences in terms of oxygen binding properties.(ABSTRACT TRUNCATED AT 400 WORDS)     

Development of homeothermy in the diving petrels Pelecanoides urinatrix exsul and P. georgicus, and the Antarctic prion Pachyptila desolata

Body temperatures of South Georgia diving petrel (P. georgicus) chicks increased from about 37.5 degrees C at hatching to between 38.5 and 39 degrees C within two weeks. Temperatures of common diving petrel P. u. exsul chicks averaged 38.8 degrees C after two weeks of age. Burrow temperatures varied between 5 and 10 degrees C. Measurements of oxygen consumption and body temperature indicated that chicks achieve effective endothermy at 5 degrees C after 9 days in P. u. exsul, 5-6 days in P. georgicus, and 0 days in the Antarctic prion (Pachyptila desolata). The maximum mass-specific, cold-induced oxygen consumption of small chicks that we could measure with our apparatus (ca. 5-6 cc O2/g per hr) was achieved at 5-6 days in P. u. exsul, 3 days in P. georgicus, and 0 days in P. desolata. Mass-specific thermal conductance decreased with age and body size in all 3 species, but was highest in P. u. exsul and lowest in P. desolata. Conductance was similar at the age of effective endothermy in all 3 species (ca. 3 J/g per hr per degrees C). The period required for the development of endothermy is related to age-specific changes in both conductance and capacity for heat production and it closely parallels the length of the brooding period. It is suggested that the length of the period of thermal dependence of the chick is related to the distance between feeding areas and the nesting site.     

Behavioral thermoregulation by hypoxic rats.

To address whether a shift in hypothalamic thermal setpoint might be a significant factor in induction of hypoxic hypothermia, behavioral thermoregulation was examined in 7 female Sprague-Dawley rats implanted with radiotelethermometers for deep body temperature (Tb) measurement in a thermocline during normoxia (PO2 = 125 torr) and hypoxia (PO2 = 60 torr). Normoxic rats (TNox) selected a mean ambient temperature of 19.7 +/- 1.4 (SE) degrees C and maintained Tb at 37.0 +/- 0.2 degrees C. Hypoxic rats selected a significantly higher ambient temperature (THox = 28.6 +/- 2.2 degrees C) but maintained Tb significantly lower at 35.5 +/- 0.3 degrees C. Without a thermal gradient (ambient temperature = 25 degrees C), Tb during hypoxia was 35.4 +/- 0.4 degrees C. The maintenance of a lower body temperature during hypoxia through behavioral thermoregulation despite having warmer temperatures available supports the hypothesis that the thermoregulatory setpoint of hypoxic rats is shifted to promote thermoregulation at a lower Tb, effectively reducing oxygen demand when oxygen supply is limited.     

Poly(ethylene glycol)-conjugation and deoxygenation enable long-term preservation of hemoglobin-vesicles as oxygen carriers in a liquid state

The stability of hemoglobin vesicles (HbV) as an oxygen infusion was tested during the storage for 1 year at 4, 23, and 40 degrees C. The surface of the HbV was modified with poly(ethylene glycol) (PEG), and the suspension was deoxygenated with nitrogen bubbling. The samples stored at 4 and 23 degrees C showed a stable dispersion state for 1 year, though the sample stored at 40 degrees C showed the precipitation and decomposition of vesicular components, a decrease in pH, and 4% leakage of total Hb after 1 year. The PEG chains on the vesicular surface stabilize the dispersion state and prevent the aggregation and fusion due to their steric hindrance. The original metHb content (ca. 3%) before the preservation gradually decreased to less than 1% in all the samples after 1 month due to the presence of homocysteine inside the vesicles which consumed the residual oxygen and gradually reduced the trace amount of metHb. The rate of metHb formation was strongly dependent on the partial pressure of oxygen, and no increase in metHb formation was observed due to the intrinsic stability of the deoxygenated Hb. Preservation at 4 and 23 degrees C slightly reduced P(50) (increased the oxygen affinity) from 38 Torr to 32 and 31 Torr, respectively. These results indicate the possibility that HbV suspension can be stored at room temperature for at least 1 year.     

Hemoglobins of the Lucina pectinata/bacteria symbiosis. I. Molecular properties, kinetics and equilibria of reactions with ligands

Three hemoglobins have been isolated from the symbiont-harboring gill of the bivalve mollusc Lucina pectinata. Oxyhemoglobin I (Hb I), which may be called sulfide-reactive hemoglobin, reacts with hydrogen sulfide to form ferric hemoglobin sulfide in a reaction that may proceed by nucleophilic displacement of bound superoxide anion by hydrosulfide anion. Hemoglobins II and II, called oxygen-reactive hemoglobins, remain oxygenated in the presence of hydrogen sulfide. Hemoglobin I is monomeric; Hb II and Hb III self-associate in a concentration-dependent manner and form a tetramer when mixed. Oxygen binding is not cooperative. Oxygen affinities are all nearly the same, P50 = 0.1 to 0.2 Torr, and are independent of pH. Combination of Hb I with oxygen is fast; k'on = (estimated) 100-200 x 10(6) M-1 s-1. Combination of Hb II and Hb III with oxygen is slow: k'on = 0.4 and 0.3 x 10(6) M-1 s-1, respectively. Dissociation of oxygen from Hb I is fast relative to myoglobin: koff = 61 s-1. Dissociation from Hb II and Hb III is slow: koff = 0.11 and 0.08 s-1, respectively. These large differences in rates of reaction together with differences in the reactions of carbon monoxide suggest differences in configuration of the distal heme pocket. The fast reactions of Hb I are comparable to those of hemoglobins that lack distal histidine residues. Slow dissociation of oxygen from Hb II and Hb III suggest that a distal residue may interact strongly with the bound ligand. We infer that Hb I may facilitate delivery of hydrogen sulfide to the chemoautotrophic bacterial symbiont and Hb II and Hb III may facilitate delivery of oxygen. The midpoint oxidation-reduction potential of the ferrous/ferric couple of Hb I, 103 +/- 8 mV, was independent of pH. Potentials of Hb II and Hb III were pH-dependent. At neutral pH all three hemoglobins have similar midpoint potentials. The rate constant for combination of ferric Hb I with hydrogen sulfide increases 3000-fold from pH 10.5 to 5.5, with apparent pK 7.0, suggesting that undissociated hydrogen sulfide is the attacking ligand. At the acid limit combination of ferric Hb I with hydrogen sulfide, k'on = 2.3 x 10(5) M-1 s-1, is 40-fold faster than combination with ferric Hb II or myoglobin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Endothermy in African platypleurine cicadas: the influence of body size and habitat (Hemiptera: Cicadidae)

The platypleurine cicadas have a wide distribution across Africa and southern Asia. We investigate endothermy as a thermoregulatory strategy in 11 South African species from five genera, with comparisons to the lone ectothermic platypleurine we found, in an attempt to ascertain any influence that habitat and/or body size have on the expression of endothermy in the platypleurine cicadas. Field measurements of body temperature (T(b)) show that these animals regulate T(b) through endogenous heat production. Heat production in the laboratory elevated T(b) to the same range as in animals active in the field. Maximum T(b) measured during calling activity when there was no access to solar radiation ranged from 13.2 degrees to 22.3 degrees C above ambient temperature in the five species measured. The mean T(b) during activity without access to solar radiation did not differ from the mean T(b) during diurnal activity. All platypleurines exhibit a unique behavior for cicadas while warming endogenously, a temperature-dependent telescoping pulsation of the abdomen that probably functions in ventilation. Platypleurines generally call from trunks and branches within the canopy and appear to rely on endothermy even when the sun is available to elevate T(b), in contrast to the facultative endothermy exhibited by New World endothermic species. The two exceptions to this generalization we found within the platypleurines are Platypleura wahlbergi and Albanycada albigera, which were the smallest species studied. The small size of P. wahlbergi appears to have altered their thermoregulatory strategy to one of facultative endothermy, whereby they use the sun when it is available to facilitate increases in T(b). Albanycada albigera is the only ectothermic platypleurine we found. The habitat and host plant association of A. albigera appear to have influenced the choice of ectothermy as a thermoregulatory strategy, as the species possesses the metabolic machinery to elevate to the T(b) range observed in the endothermic species. Therefore, size and habitat appear to influence the expression of thermoregulatory strategies in African platypleurine cicadas.     

Temperature and the respiratory properties of whole blood in two reptiles, Pogona barbata and Emydura signata

We investigated the capacity of two reptiles, an agamid lizard Pogona barbata and a chelid turtle Emydura signata, to compensate for the effects of temperature by making changes in their whole blood respiratory properties. This was accomplished by measuring the P50 (at 10, 20 and 30 degrees C), hematocrit (Hct), haemoglobin concentration ([Hb]) and mean cell haemoglobin concentration (MCHC) in field acclimatised and laboratory acclimated individuals. The acute effect of temperature on P50 in P. barbata, expressed as heat of oxygenation (deltaH), ranged from -16.8+/-1.84 to -28.5+/-2.73 kJ/mole. P50 of field acclimatised P. barbata increased significantly from early spring to summer at the test temperatures of 20 degrees C (43.1+/-1.2 to 48.8+/-2.1 mmHg) and 30 degrees C (54.7+/-1.2 to 65.2+/-2.3 mmHg), but showed no acclimation under laboratory conditions. For E. signata, deltaH ranged from -31.1+/-6.32 to -48.2+/-3.59 kJ/mole. Field acclimatisation and laboratory acclimation of P50 did not occur. However, in E. signata, there was a significant increase in [Hb] and MCHC from early spring to summer in turtles collected from the wild (1.0+/-0.1 to 1.7+/-0.2 mmol/L and 4.0+/-0.3 to 6.7+/-0.7 mmol/L, respectively).     

Body temperature of the parasitic wasp Pimpla turionellae (Hymenoptera) during host location by vibrational sounding

Abstract.  The pupal parasitoid Pimpla turionellae (L.) uses self-produced vibrations transmitted on the plant substrate, so-called vibrational sounding, to locate immobile concealed pupal hosts. The wasps are able to use vibrational sounding reliably over a broad range of ambient temperatures and even show an increased signal frequency and intensity at low temperatures. The present study investigates how control of body temperature in the wasps by endothermic mechanisms may facilitate host location under changing thermal environments. Insect body temperature is measured with real-time IR thermography on plant-stem models at temperature treatments of 10, 18, 26 and 30 °C, whereas behaviour is recorded with respect to vibrational host location. The results reveal a low-level endothermy that likely interferes with vibrational sound production because it occurs only in nonsearching females. At the lowest temperature of 10 °C, the thoracic temperature is 1.15 °C warmer than the ambient surface temperature whereas, at the high temperatures of 26 and 30 ° C, the wasps cool down their thorax by 0.29 and 0.47 °C, respectively, and their head by 0.45 and 0.61 °C below ambient surface temperature. By contrast, regardless of ambient temperature, searching females always have a slightly elevated body temperature of at most 0.30 °C above the ambient surface temperature. Behavioural observations indicate that searching females interrupt host location more frequently at suboptimal temperatures, presumably due to the requirements of thermoregulation. It is assumed that both mechanisms, producing vibrations for host location and low-level endothermy, are located in the thorax. Endothermy by thoracic muscle work probably disturbs signal structure of vibrational sounding, so the processes cannot be used at the same time.     

Energetics, body size, and the limits to endothermy

The scaling rate of metabolism with respect to body mass is analysed. Scaling of heat production implies that scaling also exists between temperature regulation and body mass. Most vertebrates follow a Kleiber relation down to a "critical mass, below which the scaling of metabolism must be changed to ensure the maintenance of endothermy. Such an adjustment is found interspecifically in birds and mammals, and is found intraspecifically in mammals during post-natal growth. If the Kleiber scaling relation is maintained below the critical mass, mammals and birds shiR from endothermic temperature regulation (above critical mass) to endothermy with obligatory torpor (below critical mass). If the Kleiber relation is followed to masses far below the critical mass, ectothermy results. Critical mass varies inversely with the level of energy expenditure, which therefore accounts for the fact that most mammals and birds are endotherms and most reptiles and fish are ectotherms. The same relationship permits the facultative endothermy found in some insects and plants.
The scaling relations existing among rate of metabolism, endothermy, and body mass can be written as a modification of the Kleiber relation. This analysis suggests that any organism, irrespective of phylogenetic position, can be endothermic at any body size, if its rate of metabolism is high enough, or can be endothermic with any rate of metabolism, if it is large enough. Consequently, it is difficult to distinguish minimal endothermy from inertial homoiothermy in animals having a large mass. The boundary conditions for effective endothermy are similar to the relationship described between metabolism and mass in the evolution of endothermy through a decrease in mass in the phylogeny of mammals. Even though endothermy may evolve with an increase in mass, its perfection may always require an evolutionary decrease in mass.     

Structural, functional, and subunit assembly properties of hemoglobin Attleboro [alpha 138 (H21) Ser----Pro], a variant possessing a site maturation at a critical C-terminal residue

Hemoglobin Attleboro, a new alpha-chain variant with a substitution of proline for serine at position 138 (H21), was found to be a noncooperative high-affinity hemoglobin (P50 = 0.26 mmHg at pH 7 and 20 degrees C) which lacked an alkaline Bohr effect. Addition of 2,3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP) led to a decrease in oxygen affinity but to no alteration in either Bohr effect or cooperativity. Ligand binding kinetics studies revealed an overall rate of oxygen dissociation at pH 7.0 and 20 degrees C that was 2.7-fold slower than that for Hb A. At pH 8.5, the kinetic profile was identical with that at pH 7, confirming the absence of a Bohr effect for this variant hemoglobin. Measurement of the rate of oxygen dissociation with carbon monoxide replacement indicated a lack of cooperativity. Sedimentation velocity experiments yielded s20,w values of 2.8 and 4.3 for 65 microM solutions of oxyhemoglobins Attleboro and A, respectively (indicating an enhancement in the oxy dimer population of this variant). Studies of the carbon monoxide combination of this variant revealed an association rate 20-fold faster than that for Hb A; only in the presence of a 1000-fold molar excess of IHP was there a significant reduction in the overall rate. Rapid-scan and traditional stopped-flow experiments conducted in the Soret Soret region demonstrated an alteration in the structure and rate of assembly of the deoxy tetramer of Hb Attleboro relative to that of Hb A. The abnormal properties of this hemoglobin variant can be attributed to major perturbations in the C-terminal region.     

Fertility results after different thawing procedures for ram semen frozen in minitubes and mini straws

The effect of different thawing procedures for ram semen frozen in minitubes and mini straws on the fertility of sheep was tested in a field trial in which 727 Norwegian crossbred ewes, aged between six months and five-and-a-half years from nine farms, were inseminated with frozen-thawed semen in natural estrous. Minitubes were thawed at 70 degrees C for 8 s (T70) and mini straws either at 70 degrees C for 5 s (S70), 50 degrees C for 9 s (S50), or 35 degrees C for 12 s (S35). Cervical insemination with 200 x 10(6) spermatozoa resulted in 25-day non-return rates of 78.7, 69.0, 73.6, and 72.9% (overall 73.6%), respectively, and lambing rates of 77.6, 66.1, 71.4, and 68.9% (overall 71.0%), respectively. There was a significantly higher lambing rate for T70 compared to S35 (P=0.03) and S70 (P=0.02), respectively, but not compared to S50 (P=0.29). Age of the ewes (P=0.02), farmers (P=0.02) and the interaction between farmer x straw type/thawing temperature (P=0.01) had a significant effect on the lambing rate. In conclusion, the superior fertility results achieved for minitubes compared to mini straws have to be carefully evaluated in relation to the possible application of a more rational semen production and simplified semen handling at AI, when using mini straws thawed at 35 degrees C.     

Blood characteristics, tracheal volume and heart mass of burrowing owls (Athene cunicularia) and bobwhite (Colinus virginianus)

1. Measurements of certain hematological and morphological characteristics were made in burrowing owls and bobwhite in search of features that could be associated with the previously described ventilatory adaptations of the burrowing owl to hypoxia and hypercarbia. 2. Values for burrowing owls and bobwhite, respectively, were: P50 = 44.9, 46.0 torr; Hct = 36.6, 38.8 vol%, Hb = 12, 12.3 (g/100 ml); RBC = 2.72 X 10(6), 3.02 X 10(6); log P50/pH = -0.412, -0.485; delta log PCO2/delta pH = -1.39, -1.585. 3. The owls had greater heart weights and smaller tracheal volumes than the bobwhite or the predicted value. 4. No hematological characteristics of the burrowing bird distinguish it from the non-burrowing bird.     

Influence of allosteric effectors and temperature on oxygen binding properties and the Bohr effect of bovine hemoglobin

The O2 binding properties of bovine Hb were examined. The increase in Cl- and DPG concentration enhanced P50. A reduction in n(max) was observed at high Cl- concentration, while DPG had little effect on n(max). An increase in Cl- concentration enhanced the Bohr effect, the magnitude of which reached a maximum at 0.1 M Cl- and 20 degrees C. This concentration is nearly equal to that at the highest slope of the log P50 vs. log [Cl-] plot, and also equal to the physiological Cl- concentration (0.1 M) of bovine blood. Furthermore, the influence of Cl- concentration on the Bohr effect is independent of temperature. On the other hand, in the absence of Cl-, bovine Hb is sensitive to DPG; an increase in DPG concentration enhanced the Bohr effect, which reached a maximum at 3 mM DPG and 20 degrees C. This concentration is nearly equal to that at the highest slope of the log P50 vs. log [DPG] plot. At low DPG concentrations, the DPG effect on the Bohr effect became small with increasing temperature, whereas at high DPG concentrations, the DPG effect was insensitive to temperature changes. At the physiological concentration of DPG (0.5 mM), increases in both Cl- concentration and temperature diminished the DPG effect. At the physiological concentrations of Cl- and DPG, the Bohr effect was -0.36 at 37 degrees C. The deltaH value at the physiological concentrations of Cl- and DPG was approximately -5.8 kcal/mol at pH 7.4. These results indicate that Cl- and temperature are important determinants of the O2 binding properties of bovine Hb.     

Structural and functional studies of the king salmon, Oncorhynchus tshawytscha, hemoglobins

Vertical starch-gel electrophoresis at pH 8.6 revealed extensive hemoglobin multiplicity with several distinct cathodal and anodal hemoglobin components. Anodal hemoglobin components are present throughout the life cycle of the king salmon. Additional cathodal components are found in the adult fish. Cathodal hemoglobin components exhibited a higher oxygen affinity (P50 = 10.2 mm at 13 degrees C, pH 7.3) than the anodal hemoglobin components (P50 = 21.8 mmHg at 13 degrees C). Oxygen binding of the anodal hemoglobins are sensitive to pH, temperature, organic phosphates (ATP and GTP), as well as, ionic strength; binding of oxygen to the cathodal hemoglobins is independent of pH and not affected by organic phosphates. Anodal hemoglobin components are less resistant to thermal denaturation over the pH 6.0 to 8.0 range. Isothermal urea denaturation of separated anodal and cathodal hemoglobin fractions of the king salmon indicate inherent differences in the stabilization energies of these hemoglobins. Autoxidation of these hemoglobins occurs around pH 7.0 and below, as well as, in the presence of increasing Cl- concentrations.     

Thermal instability of rat muscle sarcoplasmic reticulum Ca(2+)-ATPase function

To examine the thermal instability and the role of sulfhydryl (SH) oxidation on sarcoplasmic reticulum (SR) Ca(2+)-ATPase function, crude homogenates were prepared from the white portion of the gastrocnemius (WG) adult rat muscles (n = 9) and incubated in vitro for < or =60 min either at a normal resting body temperature (37 degrees C) or at a temperature indicative of exercise-induced hyperthermia (41 degrees C) with DTT and without DTT (CON). In general, treatment with DTT resulted in higher Ca(2+)-ATPase and Ca(2+) uptake values (nmol. mg protein(-1). min(-1), P < 0.05), an effect that was not specific to time of incubation. Incubations at 41 degrees C resulted in lower (P < 0.05) Ca(2+) uptake rates (156 +/- 18 and 35.9 +/- 3.3) compared with 37 degrees C (570 +/- 54 and 364 +/- 26) at 30 and 60 min, respectively. At 37 degrees C, ryanodine (300 microM), which was used to block Ca(2+) release from the calcium release channel, prevented the time-dependent decrease in Ca(2+) uptake. A general inactivation (P < 0.05) of maximal Ca(2+)-ATPase activity (V(max)) in CON was observed with incubation time (0 > 30 > 60 min), with the effect being more pronounced (P < 0.05) at 41 degrees C compared with 37 degrees C. The Hill slope, a measure of co-operativity, and the pCa(50), the cytosolic Ca(2+) concentration required for half-maximal activation of Ca(2+)-ATPase activity, decreased (P < 0.05) at 41 degrees C only. Treatment with DTT attenuated the alterations in enzyme kinetics. The increase in V(max) with the Ca(2+) ionophore A-23187 was less pronounced at 41 degrees C compared with 37 degrees C. It is concluded that exposure of homogenates to a temperature typically experienced in exercise results in a reduction in the coupling ratio, which is mediated primarily by lower Ca(2+) uptake and occurs as a result of increases in membrane permeability to Ca(2+). Moreover, the decreases in Ca(2+)-ATPase kinetics in WG with sustained heat stress result from SH oxidation.     

Effects of temperature on metabolism,ventilation, and oxygen extraction in the southern brown bandicoot Isoodon obesulus (Marsupialia: Peramelidae)

The effects of ambient temperatures (T(a)) from 10 degrees to 35 degrees C on metabolism, ventilation, and oxygen extraction were examined for the southern brown bandicoot (Isoodon obesulus). Oxygen consumption (VO2) followed the pattern typical for endotherms, decreasing with increasing T(a) from 10 degrees to 25 degrees C. It did not significantly change between Ta=25 degrees and 35 degrees C (the thermoneutral zone). VO2 was approximately 2.4 times higher at Ta=10 degrees C (0.967 mL O(2) g(-1) h(-1)) compared with basal (0.410 mL O(2) g(-1) h(-1)) at Ta=30 degrees C. While the metabolic rates of the bandicoots were basal at Ta=30 degrees C, respiratory frequency (f(R)) was 24.6 breaths min(-1), tidal volume (V(T)) was 7.79 mL, minute volume (V(I)) was 191.3 mL min(-1), and oxygen extraction efficiency (EO2) was 26.8%. Increased VO2 at Ta< or =25 degrees C was associated with a large increase in V(I) due to increases in V(T) and f(R). A greater proportion of the change was due to the increase in tidal volume. EO2 was constant at approximately 26% for all T(a) up to and including 30 degrees C. At Ta=35 degrees C, EO2 decreased to 17.7%, f(R) increased to 35.6 breaths min(-1), and V(T) decreased to 7.22 mL. The metabolic and ventilatory physiology of the southern brown bandicoot are typical of an unspecialized medium-sized marsupial.