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Biomedical subjects

P J Butler

Publications and source records attributed to P J Butler.

At least 37 records · Page 2Linked to original sources
PubMed2002

The energetics of barnacle geese (Branta leucopsis) flying in captive and wild conditions.

Experimental data on the relationship between mean heart rate (f(H)) and mean rate of oxygen consumption (VO(2)) of captive barnacle geese during flights in a wind tunnel are assessed in terms of their capacity to predict the typical VO(2) of wild barnacle geese, based on the recordings of their f(H), while undertaking autumn migratory flights between Spitsbergen (78 degrees N) and Caerlaverock, Scotland (55 degrees N). A significant linear relationship has been demonstrated between the f(H) and simultaneously recorded VO(2) of a single barnacle goose (B-B) flying in the wind tunnel (VO(2)=1.42 f(H)-304, r(2)=0.82, P<0.001, N=12 flights). Data recorded from three additional geese (N=4 flights), lay within the 95% prediction intervals of the relationship for goose B-B. When these geese (mean body mass=2.06 kg, n=4) were flown in the wind tunnel (WT) without the mask, they had a mean f(H) of 451+/-23 beats min(-1), yielding an estimate for VO(2) of 336+/-33 ml min(-1). However, f(H) has also been recorded from wild barnacle geese (mean migratory f(H) of 253 beats min(-1)), and substitution of this value into the above calibration equation results in an unrealistically low value for mean migratory VO(2) of only 55 ml min(-1). Various factors, such as differences in heart mass, selective tissue perfusion, environmental temperature and flock formation, which might account for some of the difference in f(H) between the captive and wild geese are discussed. Comparison with other WT studies shows that inter-species minimum mass-specific VO(2) declines with increasing body mass (M(b); range 0.035-2.8 kg) as 173 M(b)(-0.224), r(2)=0.848.

Animals↗
PubMed2002

The heart rate/oxygen consumption relationship during cold exposure of the king penguin: a comparison with that during exercise.

This study investigated whether exposure to low ambient temperature could be used as an alternative to exercise for calibrating heart rate (fH) against rate of oxygen consumption ((O(2))) for subsequent use of fH to estimate (O(2)) in free-ranging animals. Using the relationship between the oxygen pulse (OP, the amount of oxygen used per heart beat) and an index of body condition (or nutritional index, NI), a relationship between fH and (O(2)) was established for resting king penguins exposed to a variety of environmental temperatures. Although there was a small but significant increase in the OP above and below the lower critical temperature (-4.9 degrees C), there was no difference in the relationship obtained between the OP and body condition (NI) obtained above or below the lower critical temperature. These results were then compared with those obtained in a previous study in which the relationship between fH and (O(2)) had been established for king penguins during steady-state exercise. The relationship between OP and NI in the present study was not significantly different from the relationship between resting OP and NI in the previous study. However, the relationship was different from that between active OP and NI. We conclude that, at least for king penguins, although thermoregulation does not affect the relationship between resting OP and NI, temperature cannot be used as an alternative to exercise for calibrating fH against (O(2)) for subsequent use of fH to estimate (O(2)) in free-ranging animals.

Animals↗
PubMed2002

Heart rate and the rate of oxygen consumption of flying and walking barnacle geese (Branta leucopsis) and bar-headed geese (Anser indicus).

We tested the hypotheses that the relationship between heart rate (fH) and the rate of oxygen consumption ((O(2))) differs between walking and flying in geese and that fH and (O(2)) have a U-shaped relationship with flight speed. We trained barnacle geese Branta leucopsis (mean mass 2.1 kg) and bar-headed geese Anser indicus (mean mass 2.6 kg) to walk inside a respirometer on a treadmill and to fly in a wind tunnel with a respirometry mask at a range of speeds. We measured fH and (O(2)) simultaneously during walking on the treadmill in five individuals of each species and in one bar-headed goose and four barnacle geese during flight in the wind tunnel. The relationships between fH and (O(2)) were significantly different between flying and walking. (O(2)) was higher, and the increment in (O(2)) for a given increase in fH was greater, for flying than for walking geese. The relationship between fH and (O(2)) of free-living barnacle geese during their natural migratory flights must differ from that measured in the wind tunnel, since the fH of wild migratory birds corresponds to values of (O(2)) that are unrealistically low when using the calibration relationship for our captive birds. Neither fH nor (O(2)) varied with flight velocity across the range of speeds over which the geese would fly sustainably.

Animals↗
PubMed2001

NTF2 monomer-dimer equilibrium.

Nuclear transport factor 2 (NTF2) mediates nuclear import of RanGDP, a central component of many nuclear trafficking pathways. NTF2 is a homodimer and each chain has independent binding sites for RanGDP and nuclear pore proteins (nucleoporins) that contain FxFG sequence repeats. We show here that the monomer-dimer dissociation constant for NTF2 obtained by sedimentation equilibrium ultracentrifugation is in the micromolar range, indicating that a substantial proportion of cellular NTF2 may be monomeric. To investigate the functional significance of NTF2 dimerization, we engineered a series of point mutations at the dimerization interface and one of these (M118E) remained monomeric below concentrations of 150 microM. CD spectra and X-ray crystallography showed that M118E-NTF2 preserved the wild-type NTF2 fold, although its thermal stability was 20 deg. C lower than that of the wild-type. M118E-NTF2 bound both RanGDP and FxFG nucleoporins less strongly, suggesting that dissociation of the NTF2 dimer could facilitate RanGDP release and thus nucleotide exchange after it had been transported into the nucleus. Moreover, colloidal gold coated with M118E-NTF2 showed reduced binding to Xenopus oocyte nuclear pores. Overall, our results indicate that dimer formation is important for NTF2 function and give insight into the formation of heterodimers by mRNA export factors such as TAP1 and NXT1 that contain NTF2-homology domains.

Amino Acid Substitution↗
PubMed2001

The crystal structure of the PX domain from p40(phox) bound to phosphatidylinositol 3-phosphate.

More than 50 human proteins with a wide range of functions have a 120 residue phosphoinositide binding module known as the PX domain. The 1.7 A X-ray crystal structure of the PX domain from the p40(phox) subunit of NADPH oxidase bound to PtdIns(3)P shows that the PX domain embraces the 3-phosphate on one side of a water-filled, positively charged pocket and reveals how 3-phosphoinositide specificity is achieved. A chronic granulomatous disease (CGD)-associated mutation in the p47(phox) PX domain that abrogates PtdIns(3)P binding maps to a conserved Arg that does not directly interact with the phosphoinositide but instead appears to stabilize a critical lipid binding loop. The SH3 domain present in the full-length protein does not affect soluble PtdIns(3)P binding to the p40(phox) PX domain.

Amino Acid Sequence↗
PubMed2001

Shear stress induces a time- and position-dependent increase in endothelial cell membrane fluidity.

Blood flow-associated shear stress may modulate cellular processes through its action on the plasma membrane. We quantified the spatial and temporal aspects of the effects of shear stress (tau) on the lipid fluidity of 1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate [DiIC(16)(13)]-stained plasma membranes of bovine aortic endothelial cells in a flow chamber. A confocal microscope was used to determine the DiI diffusion coefficient (D) by fluorescence recovery after photobleaching on cells under static conditions, after a step-tau of 10 or 20 dyn/cm(2), and after the cessation of tau. The method allowed the measurements of D on the upstream and downstream sides of the cell taken midway between the respective cell borders and the nucleus. In <10 s after a step-tau of 10 dyn/cm(2), D showed an upstream increase and a downstream decrease, and both changes disappeared rapidly. There was a secondary, larger increase in upstream D, which reached a peak at 7 min and decreased thereafter, despite the maintenance of tau. D returned to near control values within 5 s after cessation of tau. Downstream D showed little secondary changes throughout the 10-min shearing, as well as after its cessation. Further investigations into the early phase, with simultaneous measurements of upstream and downstream D, confirmed that a step-tau of 10 dyn/cm(2) elicited a rapid (5-s) but transient increase in upstream D and a concurrent decrease in downstream D, yielding a significant difference between the two sites. A step-tau of 20 dyn/cm(2) caused D to increase at both sites at 5 s, but by 30 s and 1 min the upstream D became significantly higher than the downstream D. These results demonstrate shear-induced changes in membrane fluidity that are time dependent and spatially heterogeneous. These changes in membrane fluidity may have important implications in shear-induced membrane protein modulation.

Animals↗
PubMed2001

Diving beyond the limits.

Some free-ranging birds and mammals dive for periods that substantially exceed those for which their usable O(2) stores are estimated to last. The mechanisms that extend the duration of aerobic diving include marked reductions in blood flow (and hence O(2) delivery) to certain organs and tissues, passive gliding and, most probably, regional hypothermia.

Adaptation, Physiological↗
PubMed2001

Heart rate as an indicator of oxygen consumption: influence of body condition in the king penguin.

The use of heart rate to estimate field metabolic rate has become a more widely used technique. However, this method also has some limitations, among which is the possible impact that several variables such as sex, body condition (i.e. body fat stores) and/or inactivity might have on the relationship between heart rate and rate of oxygen consumption. In the present study, we investigate the extent to which body condition can affect the use of heart rate as an indicator of the rate of oxygen consumption. Twenty-two breeding king penguins (Aptenodytes patagonicus) were exercised on a variable-speed treadmill. These birds were allocated to four groups according to their sex and whether or not they had been fasting. Linear regression equations were used to describe the relationship between heart rate and the rate of oxygen consumption for each group. There were significant differences between the regression equations for the four groups. Good relationships were obtained between resting and active oxygen pulses and an index of the body condition of the birds. Validation experiments on six courting king penguins showed that the use of a combination of resting oxygen pulse and active oxygen pulse gave the best estimate of the rate of oxygen consumption V(O2). The mean percentage error between predicted and measured V(O2) was only +0.81% for the six birds. We conclude that heart rate can be used to estimate rate of oxygen consumption in free-ranging king penguins even over a small time scale (30 min). However, (i) the type of activity of the bird must be known and (ii) the body condition of the bird must be accurately determined. More investigations on the impact of fasting and/or inactivity on this relationship are required to refine these estimates further.

Animals↗
PubMed2001

Effects of sublethal ammonia exposure on swimming performance in rainbow trout (Oncorhynchus mykiss).

Adult trout Oncorhynchus mykiss fitted with a dorsal aortic catheter were exposed to 288+/-15 micromol l(-1) (mean +/- S.E.M.) total ammonia for 24h in water at a pH of 8.39+/-0.02, while swimming at a speed equivalent to 0.75 bodylengths s(-1) (BLs(-1)) in a Brett-type tunnel respirometer. The fish were then exposed to stepwise increments in swimming speed (0.25 BLs(-1) every 30 min) until exhaustion. Measurements of oxygen uptake (M(O2)) and plasma total ammonia levels and pH were made at each speed. Control trout were treated identically but without exposure to ammonia. Ammonia exposure caused an increase in plasma total ammonia level to 436+/-34 micromol l(-1), compared to 183+/-30 micromol l(-1)in control animals (N=6). A significant reduction in total plasma ammonia level was found in both groups during exercise, despite a large negative concentration gradient in those exposed to an elevated concentration of ammonia in water, which may indicate an active excretory process. The overall increase in plasma ammonia levels in exposed trout was associated with a significant reduction in critical swimming speed (U(crit)) to 1.61+/-0.17BL s(-1) from 2.23+/-0.15BL s(-1) in control animals. Ammonia-exposed trout had a significantly higher maintenance metabolic rate (MMR) than control fish, when estimated as the y-intercept of the relationship between swimming speed and M(O2). Active metabolic rate (AMR, maximum M(O2) as measured at U(crit)) was significantly lower in ammonia-exposed animals, leading to a profound reduction in factorial aerobic scope (AMR/MMR). Reduced U(crit) was also linked to a reduction in maximum tailbeat frequency. Calculation of membrane potentials (E(M)) in the white muscle of fish swum to U(crit) revealed a significant partial depolarisation of white muscle in ammonia-exposed fish. This may have prevented white muscle recruitment and contributed to the reduced maximum tailbeat frequency and overall impairment of swimming performance in the ammonia-exposed fish.

Ammonia↗
PubMed2001

The influence of locomotion on air-sac pressures in little penguins.

Air-sac pressures have been reported to oscillate with wing beat in flying magpies and with foot paddling in diving ducks. We sought to determine the impact on air-sac pressure of wing beats during swimming and of the step cycle during walking in little penguins (Eudyptula minor). Fluctuations averaged 0.16+/-0.06 kPa in the interclavicular air sacs, but only 0.06+/-0.04 kPa in the posterior thoracic sac, generating a small differential pressure between sacs of 0.06+/-0.02 kPa (means +/- S.E.M., N=4). These fluctuations occurred at approximately 3 Hz and corresponded to wing beats during swimming, indicated by electromyograms from the pectoralis and supracoracoideus muscles. There was no abdominal muscle activity associated with swimming or exhalation, but the abdominal muscles were active with the step cycle in walking penguins, and oscillations in posterior air-sac pressure (0.08+/-0.038 kPa) occurred with steps. We conclude that high-frequency oscillations in differential air-sac pressure enhance access to and utilization of the O(2) stores in the air sacs during a dive.

Abdominal Muscles↗
PubMed2001

Heart rate and rate of oxygen consumption of exercising macaroni penguins.

Twenty-four macaroni penguins (Eudyptes chrysolophus) from three groups, breeding males (N=9), breeding females (N=9) and moulting females (N=6), were exercised on a variable-speed treadmill. Heart rate (fH) and mass-specific rate of oxygen consumption (sVO2) were recorded from the animals, and both fh and sVO2 were found to increase linearly with increasing treadmill speed. A linear regression equation described the relationship between fh and sVO2 for each individual. There were no significant differences in these regressions between breeding and moulting females. There were significant differences in these relationships between all females and breeding males. fH and s VO2 were recorded from five of these animals for a total of 24 h. When fh was used to predict sVO2 for the 24 h period using the derived regressions, the estimate was not significantly different from the measured values, with an average error of -2.1 %. When fh was used to predict sVO2 for the 5 min intervals used for the calibration in all 24 birds, the estimate was not significantly different from the observed values, and the average error was only +0.47 %. Since the fH/sVO2 relationship was the same during periods of the annual cycle when the animals were inactive/fasting and active/foraging, it seems reasonable that, as long as sex differences are taken into account, fh can be used to predict the metabolic rates of free-ranging macaroni penguins all year round.

Analysis of Variance↗
PubMed2001

Seasonal hypothermia in a large migrating bird: saving energy for fat deposition?

We have tested the hypothesis that a large (2 kg) migratory bird, such as the barnacle goose Branta leucopsis, becomes hypothermic before its autumn migration, when food is not scarce, but when it is necessary to conserve and/or store energy in the form of fat. Abdominal temperature (T(ab)) was measured in wild geese using an implanted data logger. Commencing a few days before and continuing until approximately 20 days after the start of their autumn migration, mean daily T(ab) fell progressively by 4.4 degrees C. Thus, it is suggested that, rather than increasing the rate of pre-migratory fattening, the energy saved as a result of this hypothermia reduces the rate at which fat is used and thus enables its more rapid replacement following and, possibly during, migration. The energy saved may also be used for the replacement of non-fat tissues such as the locomotory muscles and gastro-intestinal tract. These observations are the first of their kind from birds in their natural environment and, together with other data, demonstrate that hypothermia in endotherms is not necessarily related to extremely low environmental temperature, to shortage of food or to the resting phase of the daily cycle. The data also highlight the relationship between hypothermia and fat deposition over extended periods in relatively large, endothermic animals and may have some relevance to obesity in humans.

Adipose Tissue↗
PubMed2000

Biophysical characterization of elongin C from Saccharomyces cerevisiae.

Elongin C (ELC) is an essential component of the mammalian CBC(VHL) E3 ubiquitin ligase complex. As a step toward understanding the role of ELC in assembly and function of CBC-type ubiquitin ligases, we analyzed the quaternary structure and backbone dynamics of the highly homologous Elc1 protein from Saccharomyces cerevisiae. Analytical ultracentrifugation experiments in conjunction with size exclusion chromatography showed that Elc1 is a nonglobular monomer over a wide range of concentrations. Pronounced line broadening in (1)H,(15)N-HSQC NMR spectra and failure to assign peaks corresponding to the carboxy-terminal helix 4 of Elc1 indicated that helix 4 is conformationally labile. Measurement of (15)N NMR relaxation parameters including T(1), T(2), and the (1)H-(15)N nuclear Overhauser effect revealed (i) surprisingly high flexibility of residues 69-77 in loop 5, and (ii) chemical exchange contributions for a large number of residues throughout the protein. Addition of 2,2,2-trifluoroethanol (TFE) stabilized helix 4 and reduced chemical exchange contributions, suggesting that stabilization of helix 4 suppresses the tendency of Elc1 to undergo conformational exchange on a micro- to millisecond time scale. Binding of a peptide representing the major ELC binding site of the von Hippel-Lindau (VHL) tumor suppressor protein almost completely eliminated chemical exchange processes, but induced substantial conformational changes in Elc1 leading to pronounced rotational anisotropy. These results suggest that elongin C interacts with various target proteins including the VHL protein by an induced fit mechanism involving the conformationally flexible carboxy-terminal helix 4.

Amino Acid Sequence↗
PubMed2000

Modulation of the oligomerization state of the bovine F1-ATPase inhibitor protein, IF1, by pH.

Bovine IF(1), a basic protein of 84 amino acids, is involved in the regulation of the catalytic activity of the F(1) domain of ATP synthase. At pH 6.5, but not at basic pH values, it inhibits the ATP hydrolase activity of the enzyme. The oligomeric state of bovine IF(1) has been investigated at various pH values by sedimentation equilibrium analytical ultracentrifugation and by covalent cross-linking. Both techniques confirm that the protein forms a tetramer at pH 8, and below pH 6.5, the protein is predominantly dimeric. By covalent cross-linking, it has been found that at pH 8.0 the fragment of IF(1) consisting of residues 44-84 forms a dimer, whereas the fragment from residues 32-84 is tetrameric. Therefore, some or all of the residues between positions 32 and 43 are necessary for tetramer formation and are involved in the pH-sensitive interconversion between dimer and tetramer. One important residue in the interconversion is histidine 49. Mutation of this residue to lysine abolishes the pH-dependent activation-inactivation, and the mutant protein is active and dimeric at all pH values investigated. It is likely from NMR studies that the inhibitor protein dimerizes by forming an antiparallel alpha-helical coiled-coil over its C-terminal region and that at high pH values, where the protein is tetrameric, the inhibitory regions are masked. The mutation of histidine 49 to lysine is predicted to abolish coiled-coil formation over residues 32-43 preventing interaction between two dimers, forcing the equilibrium toward the dimeric state, thereby freeing the N-terminal inhibitory regions and allowing them to interact with F(1).

Amino Acid Sequence↗
PubMed2000

Exposure of brown trout, Salmo trutta, to a sub-lethal concentration of copper in soft acidic water: effects upon muscle metabolism and membrane potential.

Brown trout acclimated to soft water and exposed for 96 h to a sub-lethal concentration of copper at low pH (0.08 micromol l(-1) Cu, pH 5) have a lower critical swimming speed than fish from copper-free water at neutral pH. This loss of performance is not due to difficulties in oxygen transfer resulting from gill damage since arterial oxygen and carbon dioxide levels remain unaffected. Both red and white muscle showed some metabolic disruptions consistent with local hypoxia, namely a high lactate concentration at rest and, in the white muscle, depletion of glycogen and phosphocreatine. However, a putative role of increased blood viscosity following haematological changes in reducing the supply of oxygen to the tissues is not supported by the current study. Haematocrit, haemoglobin and plasma protein concentrations were not affected by this treatment and a lack of further change in variables such as lactate at the onset of exercise led one to look for an alternative explanation for the effects of copper and low pH upon tissue metabolites. Ammonia concentration, both in the plasma and muscles, is significantly higher in trout exposed to copper and low pH. Ammonia plays a role in the regulation of a number of metabolic pathways and could contribute to the altered metabolic status of these fish. In addition, ammonium ions are known to cause electrophysiological disruptions, particularly the displacement of K(+) in ion exchange mechanisms that could lead to the observed loss of swimming performance. Using the measured distribution of ammonia between intracellular and extracellular compartments to estimate membrane potential of resting muscle, a significant depolarisation is predicted in both red and white muscle of fish exposed to copper and low pH.

Algorithms↗
PubMed2000

Heart rate and rate of oxygen consumption during flight of the barnacle goose, Branta leucopsis.

We report the first measurements of heart rate (f(H)) and the rate of oxygen consumption (V(O(2))) during flights from a species of bird larger than 500 g. V(O(2))was obtained from nine forward flapping flights of 8.9 min mean duration at a mean speed of 13.2 m s(-1) performed by three barnacle geese of mean mass 1.68 kg. Mean V(O(2))was 332 ml min(-1)or 201 ml min(-1) kg(-1). Sixteen flights were obtained from two of these birds equipped with heart rate data loggers, both when they were wearing a V(O(2)) mask and when they were not. During flights with the mask (mean duration 7.4 min), mean f(H) was 472 beats per min and during flights without the mask (mean duration 8.0 min) it was 391 beats per min. Heart rate was also measured in another goose flying without a respiratory mask and mean f(H) for all the three birds (mean mass 1.7 kg) flying without a mask for an average of 7.9 min at 13 m s(-1) was 378 beats per min. Resting f(H) for these three birds was 79 beats per min. The values of f(H) during flight are greater than those obtained from the same species during their autumn migration from Spitsbergen to southern Scotland. The possible reasons for this are discussed.

Animals↗
PubMed2000

The resting membrane potential of white muscle from brown trout (Salmo trutta) exposed to copper in soft, acidic water.

Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (E(M)) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study E(M) was directly measured in white muscle fibres of trout exposed to copper and low pH (E(M)=-52.2+/-4.9 mV) and compared with that of unexposed, control animals (E(M)=-86.5+/-2.9 mV) (means +/- s.e.m., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH(4)(+) in determining the distribution of ammonia in fish.

Acids↗