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M Guppy

Publications and source records attributed to M Guppy.

At least 37 records · Page 2Linked to original sources
PubMed1993

The role of the Crabtree effect and an endogenous fuel in the energy metabolism of resting and proliferating thymocytes.

Rat thymocytes have been used to characterize the changes in energy metabolism that occur as cells undergo a resting/proliferation transition. In the resting state, anaerobic ATP production accounts for only 4% of ATP turnover. The remainder is fueled by the oxidation of a mixture of an unidentified endogenous fuel (62%), glucose (18%) and glutamine (16%). 48 h after mitogen stimulation, the ATP turnover has increased twofold. In these proliferating cells, glucose inhibits oxygen consumption by 58%, indicating a profound Crabtree effect which is not present in resting cells. Consequently, proliferating cells, in the presence of glucose and glutamine, fuel the majority (61%) of ATP turnover anaerobically, producing lactate from glucose. The development of a Crabtree effect may be the result of the 8-10-fold increase in glycolytic enzyme activities which occurs with proliferation. Possible advantages of such a proliferative metabolism are a sparing of endogenous fuel, and a minimizing of oxidative metabolism, with its concurrent production of free radicals.

Adenosine Triphosphate↗
PubMed1993

Metabolic depression and Na+/K+ gradients in the aestivating Australian goldfields frog, Neobatrachus wilsmorei.

During aestivation the metabolic rate of the Australian goldfields frog Neobatrachus wilsmorei was reduced by 80% from its standard metabolic rate. The in vitro rate of oxygen consumption of isolated muscle and skin from aestivating frogs was up to 50% lower than that of the non-aestivating frogs. This in vitro rate of oxygen consumption was maintained for 6-12 h, indicating an intrinsic metabolic depression of tissues during aestivation. Frogs became dehydrated during aestivation. Muscle, skin and liver also became dehydrated during aestivation, but brain and kidney did not. Na+ and K+ contents and extracellular space measurement for muscle indicated that ion gradients were maintained across the muscle cell membrane during aestivation. Increases in plasma concentrations of Na+ and K+ were matched with similar increases in muscle intracellular ion concentrations. Extracellular space measurements were unsuccessful in the other tissues, but K+ content in all tissues (per dry weight) was maintained during aestivation, and the concentration of plasma K+ did not increase above that which can be accounted for by dehydration, indicating that K+ gradients were maintained.

Animals↗
PubMed1993

Quantitative study of starving platelets in a minimal medium: maintenance by acetate or plasma but not by glucose.

The requirement of donor platelets for fuels, plasma and calcium were studied using platelets washed, filtered to remove leucocytes and resuspended in a new glucose-free minimal platelet storage medium with low citrate (3 mmol/l), low buffer capacity and no calcium. This is the first study of platelets stored without plasma, glucose or calcium and it was shown that platelets continued to aggregate with collagen plus adrenaline for 48 h and showed only a 50% fall in 'swirl index', an objective morphology score, after 3 days, showing that by these criteria human platelets do not require glucose. Sodium acetate extended the storage time by between 2 and 4 days, depending on the index parameter. This is the first evidence showing that failure of platelets in these conditions is at least partly due to exhaustion of fuel, and the first evidence that acetate prolongs in vitro survival. As little as 10% low-glucose plasma extended the storage time, but it was no better than acetate. New observations using this system included a very rapid fall in pH during resuspension of the washed platelet pellet, a rising pH in the absence of added fuel and an increased pH with added acetate.

3-Hydroxybutyric Acid↗
PubMed1992

pH, temperature and lactate production in human red blood cells: implications for blood storage and glycolytic control.

The interaction of temperature and pH in biological systems comprises two components. Temperature change may perturb the pH of solutions, and it may change the pKa of some ionizable groups that are involved in enzyme catalysis. The pH optima of single reactions and whole pathways are therefore temperature sensitive. The pH optimum of glycolysis in human red cells has been investigated only at 37 degrees C. We have measured the effect of temperature on the pH of stored blood suspensions and on the pH optimum of glycolysis in the human red cell. The pH of the cell suspensions in a traditional storage medium was 7.25 +/- 0.2 at 4 degrees C. The pH optimum of glycolysis was high (7.8-8.5) between 15 and 35 degrees C. It can be inferred from our data that human red cells are currently stored at least 0.5 pH units below the pH optimum of glycolysis at 4 degrees C. This suggestion is supported by storage experiments which showed that glycolysis at 4 degrees C was at least 1.5-fold more active at an initial pH of 7.67 versus 7.36. Equations which describe the variation in reaction velocity with pH were fitted to the pH curves for glycolysis in order to identify the ionizable groups that contribute to the effect of pH on glycolysis. It is generally accepted that hexokinase catalyses the rate-limiting step in glycolysis in the human red cell, but none of the ionizable groups implicated correspond to that involved in the hexokinase reaction.

2,3-Diphosphoglycerate↗
PubMed1990

Changes in enzyme binding and activity during aestivation in the frog Neobatrachus pelobatoides.

1. The proportion of aldolase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) associated with the particulate fraction of a cell was measured in aestivating and non-aestivating Neobatrachus pelobatoides. 2. Reduced binding of these enzymes was found in the brain, indicating lower glycolytic flux. This was not correlated to metabolic rate suggesting that glycolytic rate was reduced in this tissue in the early stages of aestivation, possibly due to a change in fuel use. 3. Measurement of total enzyme levels showed that the liver of aestivating frogs had less GAPDH and less aldolase than non-aestivating frogs.

Adaptation, Physiological↗
PubMed1990

Alternative fuels for platelet storage: a metabolic study.

We have studied the metabolism of platelets in vitro using washed platelets. Oxygen uptake and fuel utilization were measured. It was found that glucose is never oxidized to any significant extent and is always converted to lactate, regardless of oxygen availability. Oxidative metabolism fuels 70-100% of the ATP turnover, and oxygen uptake is the same whether the platelet is consuming glucose, acetate or only an unidentified endogenous fuel. When acetate is the added fuel, no endogenous fuel is oxidized, whereas the addition of glucose results in sparing of only 8% of endogenous fuel. Preliminary storage experiments using plasma-free media show that an acetate-containing buffered salt solution provided excellent storage conditions and that a medium without any exogenous fuel is better than one containing glucose. Thus we conclude that a successful storage medium should contain minimal amounts of glucose, and an oxidizable fuel such as acetate, in order to supplement the endogenous one.

Acetates↗
PubMed1990

Fructose formation in stored blood.

At the high glucose concentrations used in the collection and storage of donor blood the activity of the fructose-forming polyol pathway (Reaction I and II) could act to deplete NADPH and thus GSH, thereby exposing the cells to oxidative stress. Fructose levels were found to be high in red cells and the supernatant plasma of blood collected into CP2D, which contains 258 mM glucose. Elevated fructose was not produced by the polyol pathway, but was formed by the autoclaving process. A high fructose concentration sufficient to account for the fructose in donor red cells was also found in the CP2D anticoagulant and in samples of autoclaved glucose.

Blood Donors↗
PubMed1987

Metabolism in lizards: low lactate turnover and advantages of heterothermy.

The bobtail lizard (Tiliqua rugosa) encounters environmental temperatures that range from 7 to 40 degrees C. We have studied the effects of temperature on the whole-body turnover of glucose, lactate, and fatty acid. At 35 degrees C turnover rates of glucose and fatty acid account for the majority of O2 uptake and reflect the low metabolic rate of the bobtail compared with that of a mammal of equivalent mass. Lactate turnover at rest is very low. The low rates of lactate production correlate with a lack, or relative lack, of those tissues that normally produce most of the lactate in a resting mammal, such as nonnucleated red blood cells, renal medulla, and smooth muscle associated with blood vessels. Q10 (change in rate with a 10 degrees C change in temperature) values for turnover rates of glucose and fatty acid increase as temperature decreases. It is concluded that there is an inverse temperature effect that minimizes fuel usage during torpor.

Animals↗
PubMed1987

Heart rate and body temperature during free diving of Weddell seals.

We have developed and successfully used the first microprocessor-controlled monitors for collection of data on depth, heart rate, and body temperature of one fetal and five adult male freely swimming Weddell seals. Adult seals almost invariably experienced a prompt bradycardia at the start of each dive, and the mean heart rate during diving was significantly lower for dives greater than 20 min (P greater than 0.999). The heart rate was also significantly greater during the ascent portion of dives when compared with the descent portion (P greater than 0.95). The fetal seal experienced a slow onset of bradycardia when its mother dived; during diving the fetal heart rate decreased by an average of 1.1 beats/min for each minute of the dive. The fetal heart rate generally took approximately 10 min to recover to predive levels after its mother resurfaced to breathe. The body temperature of one adult male Weddell seal showed a decrease of greater than 1.5 degrees C from resting levels before dives of greater than 15 min were initiated and a drop of over 2 degrees C before dives of greater than 30 min duration.

Animals↗
PubMed1986

Marathon fatigue: the role of plasma fatty acids, muscle glycogen and blood glucose.

The role of carbohydrate depletion in marathon fatigue was examined in 6 marathon runs. Four of the runs were potentially 'fast-time' marathons and culminated in fatigue. The utilization of carbohydrate, lipid and protein, and plasma concentrations of free fatty acids (FFA), glucose and lactate were measured at intervals throughout the runs. The contribution from protein to energy output was low (1-2%). The utilization of lipid was dependent upon plasma concentrations of FFA, which rose throughout the run. The utilization of carbohydrate mirrored that of FFA and thus fell throughout the run. Fatigue was characterized by a drop in running speed, a drop in carbohydrate utilization, an unchanging FFA utilization and a fall in blood glucose. The fall in blood glucose was not seen in the non-fatigued runners. These results are consistent with carbohydrate depletion being the cause of fatigue. The implications of these data are that lipid is the preferred fuel, but is rate-limiting, and that carbohydrate depletion, even though it causes fatigue, ensures an optimal-time marathon.

Adult↗
PubMed1986

Microcomputer-assisted metabolic studies of voluntary diving of Weddell seals.

Utilizing a microprocessor-controlled peristaltic withdrawal pump, arterial blood samples were obtained from Weddell seals (Leptonychotes weddelli) while diving voluntarily under the sea ice at McMurdo Sound, Antarctica. Plasma concentrations of glucose, lactate, free fatty acids, urea, and amino acids were determined in seals at various times during rest, diving, and recovery. In addition, radiolabeled palmitate, glucose, lactate, p-aminohippurate, inulin, galactose, and cholate were injected into the descending aorta of seals in the resting state or during voluntary diving at sea. Sequential plasma samples were collected, and the kinetics of wash-in and clearance of each component were determined. Under resting conditions, the change in specific activity of palmitate, glucose, and lactate after bolus injection followed smooth multiexponential decay kinetics as in terrestrial animals. Similar decay curves for the clearance of organ-specific compounds were also obtained in seals at rest. If, during voluntary diving, Weddell seals were analogous to exercising animals, the wash-in and clearance kinetics of all metabolites and organ-specific compounds would be qualitatively similar to those observed at rest. In contrast, wash-in and clearance appeared to be qualitatively and quantitatively modified in a way consistent with utilization of the classical Scholander diving response in both short and long dives.

Amino Acids↗
PubMed1986

Hemoglobin concentrations and blood gas tensions of free-diving Weddell seals.

Arterial blood gas tensions, pH, and hemoglobin concentrations were measured in four free-diving Weddell seals Leptonychotes weddelli. A microprocessor-controlled sampling system enabled us to obtain 24 single and 31 serial aortic blood samples. The arterial O2 tension (PaO2) at rest [78 +/- 13 (SD) Torr] increased with diving compression to a maximum measured value of 232 Torr and then rapidly decreased to 25-35 Torr. The lowest diving PaO2 we measured was 18 Torr just before the seal surfaced from a 27-min dive. A consistent increase of arterial hemoglobin concentrations from 15.1 +/- 1.10 to 22.4 +/- 1.41 g/100 ml (dives less than 17 min) and to 25.4 +/- 0.79 g/100 ml (dives greater than 17 min) occurred during each dive. We suggest that an extension of the sympathetic outflow of the diving reflex possibly caused profound contraction of the Weddell seal's very large spleen (0.89% of body wt at autopsy), although we have no direct evidence. This contraction may have injected large quantities of red blood cells (2/3 of the total) into the seal's central circulation during diving and allowed arterial O2 content to remain constant for the first 15-18 min of long dives. The increase of arterial CO2 tensions during the dive and the compression increase of arterial N2 tensions were also moderated by injecting red blood cells sequestered at ambient pressure. After each dive circulating red blood cells are oxygenated and rapidly sequestered, possibly in the spleen during the first 15 min of recovery.

Animals↗
PubMed1985

Seal lungs collapse during free diving: evidence from arterial nitrogen tensions.

Arterial blood nitrogen tensions of free-diving Weddell seals (Leptonychotes weddelli) were measured by attaching a microprocessor-controlled blood pump and drawing samples at depth to determine how these marine mammals dive to great depths and ascend rapidly without developing decompression sickness. Forty-seven samples of arterial blood were obtained from four Weddell seals during free dives lasting up to 23 minutes to depths of 230 meters beneath the sea ice of McMurdo Sound, Antarctica. Peak arterial blood nitrogen tensions of between 2000 and 2500 millimeters of mercury were recorded at depths of 40 to 80 meters during descent, indicating that the seal's lung collapses by 25 to 50 meters. Then arterial blood nitrogen tensions slowly decreased to about 1500 millimeters of mercury at the surface. In a single dive, alveolar collapse and redistribution of blood nitrogen allow the seal to avoid nitrogen narcosis and decompression sickness.

Animals↗
PubMed1983

Metabolic adjustments to diving and recovery in the African lungfish.

The metabolic potentials of the heart, brain, white muscle, and liver in the African lungfish were estimated by enzymatic data. Metabolic effects of a 12-h submergence were monitored using metabolite measurements. Heart was the most oxidative tissue but also showed the greatest anaerobic potential. The brain displayed relatively low oxidative capabilities. White muscle remained almost inert. Although high-energy phosphate concentrations in brain and heart did not fall during submergence, glycolysis was activated as indicated by crossover plots, depletion of endogenous glycogen stores, and lactate accumulation. Blood-tissue lactate and glucose gradients indicated 1) that the heart and brain released lactate throughout submergence, 2) that after 12 h of submersion the brain and heart were probably obtaining all their required glucose from the blood, 3) that the liver released glucose throughout submergence, and 4) that white muscle was metabolically isolated from the rest of the body during submergence. It appeared that perfusion adjustments occurring during submergence were directed more toward regulating intertissue exchange of metabolites than toward oxygen conservation. Comparisons are made to diving responses in mammals.

Anaerobiosis↗
PubMed1982

The hare and the tortoise: metabolic strategies in cardiac and skeletal muscles of the skink and the chameleon.

Two lizards--a skink capable of fast short dashes, and a chameleon, incapable of fast movement--have been studied to determine the degree of metabolic diversity that exists in this group of reptiles. Oxygen uptake measurements, skeletal muscle histochemistry, and enzyme and metabolite levels in cardiac and skeletal muscles reveal that the skink has a higher metabolic potential, both aerobic and anaerobic, than the chameleon. The difference, however, is not as large as is indicated by the behaviors of the two lizards. Levels of citrate synthase and B-hydroxybutaryl CoA dehydrogenase in the hearts of both the lizards are high and indicate mammalian-level metabolic capabilities.

Animals↗
PubMed1981

An ultrastructural and histochemical study of the axial musculature in the African lungfish.

Red, intermediate, and white axial muscle fibres of African lungfish were studied using histochemical techniques and electron microscopy. Gross dissection revealed the presence of a small wedge of red coloured muscle along the lateral line. This wedge was shown by histochemical demonstrations of lactate and succinate dehydrogenases, of adenosine triphosphatases, and of lipid to be composed of a mosaic of red and intermediate fibres measuring 23.63 and 34.30 micrometer in average diameter, respectively. The bulk of the myotome was composed of white fibres having an average diameter of 67.35 micrometer. Mitochondrial density, capillarity and lipid content were very low for all fibres. These data suggest that the axial musculature is geared primarily for anaerobic function. The mosaic arrangement of fibres, and the lack of a subsarcolemmal band of mitochondria suggests that the lungfish have a muscle organisation that is transitional between lower vertebrates and amphibians.

Adenosine Triphosphatases↗
PubMed1979

Metabolic sources of heat and power in tuna muscles. I. Muscle fine structure.

As part of an investigation into the generation of muscle heat in the tuna, the histochemistry and ultrastructure of the myotomal muscles were studied. Both red and white fibres are differentiated into two forms. The two forms of red muscle are very similar except for differential electron absorbance and different kinds of glycogen granules stored. In both forms, capillarity, mitochondrial numbers, and intracellular lipid droplets are abundant, implying the potential for a vigorous aerobic metabolism. During bursts of swimming, glycogen granules and intracellular lipid droplets are both largely depleted. The two types of white fibre differ in electron absorbance, pinocyotic activity, glycogen abundance, and insertion pattern, all of which are more pronounced in the 'dense' fibre form. Several features of tuna white muscle are unique or unusually developed. Thus, tuna muscle contains more glycogen than does red muscle. Glycogen granules may be randomly dispersed in myofibrillar or peripheral regions or may be sequestered in membrane-bound structures termed glycogen bodies. During short bursts of swimming, glycogen granules from all storage sites are mobilized. The white muscle has an ample capillary supply, small, but significant, amounts of intracellular lipid, and unusual numbers of mitochondria.

Animals↗