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Biomedical subjects

R M Wells

Publications and source records attributed to R M Wells.

At least 19 recordsLinked to original sources
PubMed2001

The aerobic physiology of the air-breathing blue gourami, Trichogaster trichopterus, necessitates behavioural regulation of breath-hold limits during hypoxic stress and predatory challenge.

Physiological characteristics of the blood oxygen transport system and muscle metabolism indicate a high dependence on aerobic pathways in the blue gourami, Trichogaster trichopterus. Haemoglobin concentration and haematocrit were modest and the blood oxygen affinity (P50=2.31 kPa at pH 7.4 and 28 degrees C) and its sensitivity to pH (Bohr factor, phi=-0.34) favour oxygen unloading at a relatively high oxygen pressure (PO2). The intracellular buffering capacity (44.0 slykes) and lactate dehydrogenase (LDH) activity (154.3 iu g(-1)) do not support exceptional anaerobic capabilities. Air-breathing frequency in the blue gourami is expected to increase when aquatic oxygen tensions decline. Under threat of predation, however, this behaviour must be modified at a potential cost to aerobic metabolism. We therefore tested the hypothesis that metabolic responses to predatory challenge and aquatic hypoxia are subject to behavioural modulation. Computer-generated visual stimuli consistently reduced air-breathing frequency at 19.95, 6.65 and 3.33 kPa PO2. Bi-directional rates of spontaneous activity were similarly reduced. The metabolic cost of this behaviour was estimated and positively correlated with PO2 but not with visual stimulation thus indicating down-regulation of spontaneous activity rather than breath-holding behaviour. Neither PO2 nor visual stimulation resulted in significant change to muscle lactate and ATP concentrations and confirm that aerobic breath-hold limits were maintained following behavioural modulation of metabolic demands.

Adaptation, Physiological↗
PubMed2001

Metabolic characteristics of muscles in the spiny lobster, Jasus edwardsii, and responses to emersion during simulated live transport.

The metabolic characteristics of five muscle groups in the spiny lobster Jasus edwardsii were examined in order to compare their anaerobic and oxidative capacities. Enzyme activities of phosphorylase, phosphofructokinase, pyruvate kinase, and lactate dehydrogenase were highest in abdominal muscles supporting anaerobic burst activity. Hexokinase, citrate synthase, and HOAD activities in the leg and antennal muscles indicated higher aerobic potential. Arginine kinase activities were high in all muscle groups indicating that muscle phosphagens are an important energy reserve. Arginine phosphate concentrations in 4th periopod and abdominal flexor muscle from lobsters sampled in the field were higher than any values from captive animals, and approximately five times those for ATP. Muscle lactates were high in captive animals. Responses to emersion during simulated live transport appear to exploit the capacity for functional anaerobiosis and further differentiated the muscle groups. Abdominal muscles were especially sensitive and after 24 h showed significant increases in lactate, glucose, ADP, and AMP. ATP levels appeared to be maintained by muscle phosphagens and raised doubts about the efficacy of the adenylate energy charge in evaluating the emersion response. Haemolymph glucose, lactic acid, and ammonia peaked after 24 h emersion and were largely restored following re-immersion. We propose that arginine phosphate concentrations in the 4th periopod are an appropriate index of metabolic stress, and could lead to improved commercial handling protocols.

Adenosine Triphosphate↗
PubMed2001

Ontogenetic changes in enzyme activities associated with energy production in the spiny lobster, Jasus edwardsii.

The larval life of the spiny lobster Jasus edwardsii is one of the longest and most complex of any marine organism and is poorly understood due to the difficulty of studying cryptic, pelagic organisms. Hence, the capacity for active swimming in the phyllosoma, puerulus and juvenile stages and the use of possible metabolic fuel reserves was inferred from a number of enzyme activities, including citrate synthase, lactate dehydrogenase, and HOAD. High activities of CS and LDH in abdominal tissues of Stage 11 phyllosoma and pueruli are consistent with a capacity to commence active on-shore movement. The activities of LDH and HOAD showed positive allometry while CS was independent of body mass. The body mass dependence of LDH activity may reflect the developing ability of the lobster to initiate brief escape manoeuvres, and the scaling of HOAD reflects an increased use of lipid fuel reserves. Aerobic enzyme activities were higher in abdominal tissues than in cephalic tissues of pelagic pueruli, but high activities appear in the cephalic tissues of juveniles. These changes mirror a developmental shift in activity from pelagic oceanic swimming to a benthic existence on the seabed of the near shore. The low LDH activity in pueruli confirmed previous findings that they have limited feeding capacity, with carbohydrate contributing little towards the major energy reserves. The highest LDH activities occur in the abdominal muscles of juveniles and correlate with rapid tail-flicking escape behaviour. The activities of HOAD increased throughout development, and in the abdominal tissues of juveniles, may reflect lipid transformation and accumulation as an energy reserve. Enzyme activities, therefore, provide useful information concerning migratory behaviour that is presently unavailable from ecological studies.

Animals↗
PubMed1999

Evolution of haemoglobin function: molecular adaptations to environment.

1. Nearly 1000 mutations have been described for human haemoglobin (Hb), many of which result in subtle changes to the oxygen transport system. Similar changes have occurred over the course of animal evolution resulting in a diversity of functional attributes which appear to correlate the availability of oxygen in the environment with metabolic demand. 2. At an early stage in evolution, worm-like animals had large, polymeric aggregations of Hb subunits circulating through primitive circulatory systems and some possessed monomeric Hb in blood cells functioning as an oxygen store. 3. The circulating vertebrate red blood cell provides an environment allowing haem units to interact among themselves and with various organic phosphates to allow a responsive and highly regulated system of gas transport. During metazoan evolution the burden of physiological regulation has shifted from the cells to organ systems, as endothermy and aerial breathing permit a relatively constant environment. 4. An understanding of the adaptive possibilities of Hb has helped us to understand the ontogeny of oxygen transport and to interpret recently described functional properties of human embryonic haemoglobins.

Adaptation, Biological↗
PubMed1997

The control of oxygen affinity in the three human embryonic haemoglobins by respiration linked metabolites.

The effect of CO2, ATP and lactate ions on the oxygen affinity of the three human embryonic haemoglobins have been studied. CO2 lowers the affinity of both the adult and embryonic haemoglobins for oxygen, as does ATP. The ATP effect follows a simple binding process with an equilibrium constant in the mM range. Lactate ions have no effect on the oxygen equilibrium process, over the concentration range studied. These findings are discussed in terms of the likely physiological conditions experienced by human embryonic red blood cells.

Adenosine Triphosphate↗
PubMed1995

Infection of humans and horses by a newly described morbillivirus.

OBJECTIVE: To describe the clinical and epidemiological features of an outbreak of a viral infection affecting humans and horses. SETTING: Stables in Hendra, a suburb of Brisbane. SUBJECTS: Affected horses and humans, and at-risk human contacts. RESULTS: A pregnant mare died two days after arrival from a paddock elsewhere in Brisbane. Eight to 11 days later, illness (depression, anorexia, fever, dyspnoea, ataxia, tachycardia, tachypnoea and nasal discharge) was reported among 17 other horses from the same or an adjoining stable. Fourteen horses died or were put down. Five and six days after the index mare's death, a stable-hand and then a horse-trainer, both of whom had had close contact with the sick mare's mucous secretions, developed influenza-like illnesses. The stable-hand recovered but the trainer developed pneumonitis, respiratory failure, renal failure and arterial thrombosis, and died from a cardiac arrest seven days after admission to hospital. A morbillivirus cultured from his kidney was identical to one isolated from the lungs of five affected horses. The two affected humans and eight other horses were seropositive for the infection, which was reproduced in healthy horses following challenge by spleen/lung homogenates from infected horses. There was no serological evidence of infection in 157 humans who had had contact with the stables or the sick horses or humans. CONCLUSIONS: A previously undescribed morbillivirus infected a probable 21 horses and two humans; one human and 14 horses died. That no further cases were detected among humans suggests that the virus was of low infectivity. The source of infection remains undetermined.

Adult↗
PubMed1993

Hb Howick [beta 37(C3)Trp-->Gly]: a new high oxygen affinity variant of the alpha 1 beta 2 contact.

Hb Howick or beta 37(C3) Trp-->Gly is a newly described hemoglobin variant found in an adult male. Hematological data and stability by the isopropanol stability test were normal. The abnormal variant comprised 29% of total hemoglobin and migrated in the Hb D position on cellulose acetate at pH 8.6, and in the Hb F position on citrate agar (pH 6.0). Oxygen dissociation studies on the whole blood showed the variant to have a higher oxygen affinity than normal, with a P50 of 19.8 mm Hg (normal, 26 mm Hg). There were also significant differences in the saturation curve. The variant showed a reduced Bohr effect which was manifested as very high oxygen affinity at low pH and saturation. The beta 37 residue is an alpha 1 beta 2 contact site and the substitution of the tryptophan for a glycine would be expected to result in a destabilization of the deoxy-hemoglobin form because of the reduced number of hydrogen bonds, salt bridges and van der Waal contacts between the alpha 1 and beta 2 chains.

Adult↗
PubMed1989

Adenylate energy charge and hemoglobin function in developing mouse embryos.

1. Adenylate energy charge (EC) was measured in mouse embryos and showed a significant rise from 0.79 at day 11 of gestation to 0.87 at day 15 (P less than 0.05). 2. The low value of EC between days 11 and 13 corresponds with the predominance of the embryonic hemoglobin fraction E-I which has high affinity and poor cooperativity. 3. The highest value of EC corresponds with the predominance of adult hemoglobin which has lower affinity and cooperative oxygen binding. 4. Weight-specific oxygen uptake rates of isolated embryos decreases with weight gain and it is suggested that the energy charge is a manifestation of metabolic regulatory processes which sustain embryonic growth.

Adenine Nucleotides↗
PubMed1989

Allosteric transition in hemoglobin (alpha 2A beta 2I) from the rhynchocephalian reptile relict Sphenodon punctatus.

The major hemoglobin component Hb A of the tuatara, Sphenodon punctatus, a relict of the rhynochocephalian reptiles that lived 200 million years ago, was investigated in the light of the apparent contradiction inherent in an effect of organic phosphate cofactors on the oxygen affinity of hemoglobins exhibiting hyperbolic oxygen equilibrium curves. The heterotropic allosteric effect of ATP, the major erythrocytic cofactor in the tuatara, is shown to be correlated with distinct homotropic interactions (Hill's cooperativity coefficient at half-saturation, n50, attaining 1.3-1.5 above pH 7.5), and with free energies of heme-heme interaction (4.7 kJ.mole-1 at pH 7.2) which resemble those in other vertebrate hemoglobins that exhibit higher n50 values. Curiously, chloride ions increase hemoglobin-oxygen affinity below pH +/- 7.2. The possible mechanisms underlying the effects of ATP and chloride are discussed.

Adenosine Triphosphate↗
PubMed1988

A kinetic and equilibrium study of ligand binding to the monomeric and dimeric haem-containing globins of two chitons.

The radular muscles of the amphineuran molluscs Amaurochiton glaucus and Sipharochiton pelliserpentis contain both a dimeric and a monomeric form of myoglobin. The dimeric form of the protein is composed of two polypeptide chains covalently linked to each other via one or more disulphide bonds. The dimeric protein shows co-operative O2-binding curves. Kinetic investigations indicate that CO binding is co-operative in the dimeric protein, subsequent to full photolysis, but mono-exponential following 10% photolysis. O2 recombination following part photolysis is mono-exponential in the dimeric form, whereas O2 dissociation kinetics indicates the presence of chain heterogeneity. The monomeric form of the protein exhibits mono-exponential time courses in all the experimental situations explored. Although the rate constants associated with the reactions of individual dimer and monomer molecular species are very different, the two species of chiton investigated show remarkably similar properties when compared with each other. All the reactions studied are pH-independent in the range pH 6-8. Amino acid analysis indicates that the monomeric units that combine to form the dimeric species are not identical with the naturally occurring monomeric form. A comparison is made between the chiton myoglobins and other similar O2-binding proteins.

Amino Acids↗
PubMed1988

Primary structure of the hemoglobins from Sphenodon (Sphenodon punctatus, Tuatara, Rynchocephalia). Evidence for the expression of alpha D-gene.

Sphenodon is the sole representative of the "beakhead" reptiles which were widely distributed during the Triassic period before the spectacular rise of dinosaurs. Sphenodon punctatus is the only survivor ("living fossil") of this period. The morphological features of Sphenodon are remarkably conservative and differ little from reptiles living 200 million years ago. In the present paper the determination of the primary structure of the tetrameric hemoglobins is described: three components are identified: hemoglobin A' (alpha A2 beta II2), hemoglobin A (alpha A2 beta I2) and hemoglobin D (alpha D2 beta II2). The components were characterized electrophoretically, the four different peptide chains were characterized by Triton electrophoresis as well as by high-performance liquid chromatography. The hemoglobins and--under dissociating conditions--also the chains, were isolated on columns of cellulose ion exchangers. Sequence determination was carried out after cleavage of the individual chains with trypsin and after a specific chemical cleavage of the Asp-Pro bond. For sequence determination the film technique and gas-phase method were employed. The data are compared with the sequence of the human hemoglobin, and interpretations of the amino-acid sequences are given. Particularly notable is the evidence of hemoglobin D: this hemoglobin (alpha D2 beta II2) is found only in birds, and in two cases in turtles. However, this component is not found in other reptiles. The results make possible an interpretation of the relatively high oxygen affinity and explain the lack of cooperativity (myoglobin properties) of these tetrameric hemoglobins.

Amino Acid Sequence↗
PubMed1987

Respiration of antarctic fish from McMurdo Sound.

1. Resting rates of oxygen uptake were measured for nine species of unstressed fish living at -1.8 degree C in McMurdo Sound, Antarctica (77-78 degrees S). Interspecific differences in VO2 were correlated with the habits and activity of the fish. 2. The cryopelagic Pagothenia borchgrevinki regulated oxygen uptake down to a critical PO2 of approximately 60 mmHg. The inactive benthic species Trematomus centronotus extracted oxygen to lower PO2 and appeared to have a lesser degree of oxyregulation when the data were analysed using a quadratic model. 3. Cutaneous oxygen uptake in the nototheniids T. bernacchii and P. borchgrevinki amounted to 9 and 17% of total VO2 under normoxic conditions which is less than that reported for scaleless Antarctic fish. 4. The contentious concept of metabolic cold adaptation in polar fish has been reviewed, and the opinion expressed that the phenomenon cannot be dismissed on the grounds of technically incompetent measurement, or through inappropriate extrapolation of data from fish at lower latitudes.

Animals↗
PubMed1987

On-line detection of reversible myocardial ischemic injury by measurement of myocardial electrical impedance.

The metabolic and physiological alterations associated with changes in myocardial tissue electrical resistivity during ischemia were characterized to assess the feasibility of using such resistivity as an on-line indicator of the onset of ischemic injury. Twelve anesthetized dogs underwent rapid cardiac extirpation; 5 served as untreated controls, and 7 were pretreated with metoprolol tartrate. Beta blockade was used to alter the time course of ischemic injury as demonstrated previously in studies using this experimental model. In vitro measurement of myocardial resistivity, the detection of ischemic contracture, and serial measurements of tissue adenosine triphosphate (ATP) and lactate were obtained from totally ischemic left ventricles at 37 degrees C. Myocardial resistivity began to increase significantly before onset of ischemic contracture in the untreated control group (resistivity at 42.3 +/- 3.1 minutes, contracture at 53.8 +/- 3.7 minutes; p less than 0.025) as well as the metoprolol group (resistivity at 50.7 +/- 1.5 minutes, contracture at 70.0 +/- 3.5 minutes; p less than 0.005). As expected, ischemic contracture was delayed in the beta-blocked group compared with controls (p less than 0.01). Similarly, the onset of myocardial resistivity increase was delayed in the beta-blocked group (p less than 0.025). ATP and lactate levels at the onset of myocardial resistivity increase were consistent with severe but reversible injury. Resistivity changes during ischemia correlated linearly with simultaneous ATP depletion and lactate accumulation (r = 0.88 to 0.98; p less than 0.05). Furthermore, during global ischemia studied in 3 anesthetized dogs in vivo, the onset of myocardial resistivity increase occurred after 20 minutes. Finally, 6 anesthetized dogs underwent 60 minutes of in vivo regional ischemia by coronary artery occlusion, followed by 60 minutes of reperfusion. Myocardial resistivity in the ischemic region increased immediately and steadily after coronary occlusion, followed by a rapid decrease during subsequent reperfusion. These data show that myocardial resistivity may be useful for identifying severe but still reversible ischemic injury in on-line fashion during regional and global myocardial ischemia.

Adenosine Triphosphate↗
PubMed1986

Effects of sustained swimming on rainbow trout muscle structure, blood oxygen transport, and lactate dehydrogenase isozymes: evidence for increased aerobic capacity of white muscle.

Groups of rainbow trout (Salmo gairdneri, Richardson) were continuously swum at 20 cm s-1 (1.0 body lengths s-1) for 0, 3, 30, and 200 days. No significant changes in fish condition factor, combined red and white muscle mass, muscle fibre size or fibre size distribution were observed. After 200 days of swimming there was a significant 2.2 fold increase in red muscle mass. Number of capillaries per red muscle fibre increased significantly in each group by a maximum of 27% after 200 days exercise. Number of capillaries per white muscle fibre increased significantly by 95% after 200 days exercise. Blood lactate, haemoglobin (Hb) concentration haematocrit, erythrocyte adenosine triphosphate, and whole blood oxygen affinity P50 were unchanged by swimming. After 30 and 200 days swimming there was a shift in expression of white muscle lactate dehydrogenase (LDH) isozymes from LDH-A to LDH-B. Within the duplicated LDH-B isozyme complex, there was a shift in expression from LDH-B to LDH-B' subunits. These results suggest that sustained swimming at 1(-1) bl s-1 increased the aerobic capacity of red and particularly white (fast) muscle of rainbow trout but did not alter the gas transport characteristics of the blood.

Aerobiosis↗