Rate Of Energy Use Research Articles

Coulometric measurement of oxygen consumption during development of marine invertebrate embryos and larvae

Determining the metabolic rate of larval invertebrates from aquatic habitats is complicated by the problems of small size and the scarcity of suitable measurement techniques. In this study, coulometric respirometry (a new technique for the study of marine embryos and larvae) was used to explore several issues associated with the rate of energy use during embryonic and larval development of marine invertebrates from three phyla. Coulometric respirometry measures rates of oxygen consumption under normoxic conditions by electrochemically replacing the oxygen consumed by organisms during an experiment. This technique is based on the assumption that all electrons consumed by the anodic reactions result in the production of oxygen. We verify this assumption using direct measurements of oxygen production and show that the technique is sensitive enough (1 nmol O2 h-1) to quantify the oxygen consumption of a single individual swimming freely in a relatively large volume (2 ml). Continuous measurements can span days, and embryos in the coulometric respiration chambers develop to the larval stage at normal rates of differentiation. Measurements of metabolic rates were made with the coulometric respirometer during the complete life-span of larvae of three species (asteroid, Asterina miniata; bivalve, Crassostrea gigas; echinoid, Dendraster excentricus). For these species, metabolic power equations had mass exponents near unity (0.9­1.1), showing that metabolic rate scales isometrically with mass during larval growth. Metabolic rates were independent of the concentration of larvae used in the respirometer chambers for a range of larval concentrations from 4 to 400 larvae ml-1 (coulometric respirometer) and from 241 to 809 larvae ml-1 (polarographic oxygen sensor). Metabolic rates were measured using coulometric respirometry and two other commonly used techniques, polarographic oxygen sensors and Winkler's titration. Polarographic oxygen sensors in small, sealed chambers (100 µl) consistently gave the lowest values (by as much as 80 %) for the asteroid, echinoid and molluscan larvae. By comparison, rates of oxygen consumption measured using coulometric respirometry and Winkler's titration (to measure the change in oxygen concentration over time) were similar and consistently higher. Although the polarographic oxygen sensor is the most widely used method for measuring the metabolism of small animals in sealed 100­1000 µl chambers, it appears that the metabolism of some larvae is adversely affected by the conditions within these respirometers.

Feeding, Energy Processing Rates and Egg Production in Painted Lady Butterflies

ABSTRACT Volume and energy ingestion rates, meal sizes (intakes to satiation) and meal frequencies were measured for previously unfed adult painted lady butterflies (Vanessa cardui L.) fed sucrose solutions or nectar from Lantana camera flowers in the laboratory. Volume and energy rates of crop emptying, assimilation efficiencies and mature egg production over 1 week were measured for V. cardui fed on sucrose solutions to assess mechanisms for and consequences of maximizing net meal energy. Viscosity reduced volume ingestion rates as sugar concentration increased, and 35–52.5% (w/v) sucrose produced a maximum rate of energy gain from sucrose solutions. Ingestion rates were lower from Lantana flowers. Increasing Lantana nectar concentration from 33 to 70% sucrose would produce about the same rate of energy gain for a meal. Virtually all ingested sugars were assimilated. Energy processing rates of 30 μl meals did not vary with sex, varied little with concentration and were 12–30 times the rate of energy use for maintenance. For females this may be due to the linear dependence of mature egg production on the amount of sugar ingested. Average meal timing compensated for variations in food concentration. Meals may be initiated before complete crop emptying, and this would increase the overall rates of energy processing, particularly for small meals. If Vanessa are not time-constrained while foraging, selecting concentrated nectars would decrease foraging frequency and increase the number of mature eggs produced after a meal.

Population and the energy problem

When energy is scarce or expensive, people can suffer material deprivation and economic hardship. When it is obtained in ways that fail to minimize environmental and political costs, these too can threaten human wellbeing in fundamental and pervasive ways. The energy problem today combines these syndromes: much of the world's population has too little energy to meet basic human needs; the monetary costs of energy are rising nearly everywhere; the environmental impacts of energy supply are growing and already dominant contributors to local, regional, and global environmental problems (including air pollution, water pollution, ocean pollution, and climate change); and the sociopolitical risks of energy supply (above all the danger of conflict over oil and the links between nuclear energy and nuclear weapons) are growing too. This predicament has many causes, but predominant among them are the nearly 20-fold increase in world energy use since 1850 and the cumulative depletion of the most convenient oil and gas deposits that this growth has entailed, resulting in increasing resort to costlier and/or environmentally more disruptive energy sources. The growth of world population in this period was responsible for 52% of the energy growth, while growth in per capita energy use was responsible for 48% (excluding causal connections between population and energy use per capita). In the United States in the same period, population growth accounted for 66% of the 36-fold increase in energy use. In the late 1980s, population growth was still accounting for a third of energy growth both in the United States and worldwide. Coping with global energy problems will require greatly increased investment in improving the efficiency of energy enduse and in reducing the environmental impacts of contemporary energy technologies, and it will require financing a transition over the next several decades to a set of more sustainable (but probably also more expensive) energy sources. The difficulty of implementing these measures will be greatest by far in the developing countries, not least because of their high rates of population growth and the attendant extra pressures on economic and managerial resources. If efficiency improvements permit delivering the high standard of living to which the world aspires based on a per capita rate of energy use as low as 3 kilowatts—about a quarter of the current U.S. figure—then a world population stabilized at 10 billion people would be using energy at a rate of 30 terawatts, and a population of 14 billion would imply 42 terawatts (compare 13.2 terawatts in 1990). Delivering even the lower figure at tolerable monetary and environmental costs will be difficult; each additional billion people added to the world population will compound these difficulties and increase energy's costs, making everyone poorer.

The cellular basis of contraction and relaxation in cardiac and vascular smooth muscle

Changes in cytoplasmic levels of free-ionized calcium regulate the contraction and relaxation of cardiac and vascular smooth muscle. Aside from changing the intrinsic rate of energy use within the cell, an intervention that alters the strength of contraction of cardiac or vascular smooth muscle must in general alter either the intracellular calcium level, change the calcium requirements of the contractile apparatus, or exert both effects. Intracellular calcium handling is modulated by at least three other important second messengers: cyclic adenosine monophosphate, cyclic guanosine monophosphate, and inositol 1,4,5 triphosphate. These substances modulate intracellular calcium handling at multiple steps in the excitation-contraction coupling scheme. In vascular smooth muscle, diacylglycerol appears to play an important role in the regulation of myofilament calcium requirements. Intracellular calcium homeostasis is maintained through the action of sarcolemmal mechanisms that extrude calcium into the extracellular space; these mechanisms include a sodium-calcium exchange mechanism and an energy-dependent calcium pump. Abnormalities in electrophysiologic properties, sarcoplasmic reticulum function, energy use and supply, and contractile element interaction have been identified in experimental studies of animals and patients with various cardiovascular diseases. These abnormalities may be differentially affected by therapeutic agents that act on the heart or vasculature; therefore it is important to understand the underlying cellular abnormalities and subcellular actions of inotropic, vasoconstrictor, and vasodilatory drugs to apply rational therapeutics in the clinical setting.

Influence of Gut Metabolism on Nutrient Supply in Ruminants: Introduction

Much is known about gut metabolism and gut in volvement in nutrient absorption. Yet a more complete understanding of the mechanisms involved in nutrient transport, of the numerous factors regulating and/or influencing nutrient transport and of the extensive met abolic activity of gut tissues is needed. This symposium reviews three areas of gut nutrient transport and meta bolic activity that have been undergoing considerable research in recent years. lonophores are commonly used feed additives in the production of both ruminants and poultry. It is well established that ionophores influence rumen microbial metabolism, with the primary result being a relatively greater proportion of propionate and a relatively lesser proportion of acetate being formed in the rumen from carbohydrate fermentation. The anticoccidial proper ties of ionophores contribute to their wide use in poultry production. Becausevarious cations may be selectively bound by ionophores, because these cations may be important nutrients to be absorbed and because these cations may play critical roles in nutrient transport, we must consider the potential influence ionophores may have on nutrient absorption. The involvement of iono phores in nutrient digestion and absorption is discussed by Spears (1). In ruminants, much information is available describ ing the influence of dietary change on the production of end products of microbial fermentation, primarily in the reticulorumen but also in the large intestine. Even though absorption and metabolism of volatile fatty acids by tissues of the reticulorumen have been studied for many years, it is not completely understood how these tissues may influence the availability of nutrients to peripheral tissues. Also, factors that affect the devel opment and expression of nutrient uptake by the enterocytes are of interest. Information is emerging regarding the interaction of the microbial flora of the gut and nutrient absorption. Parker (2)presents a discussion of how the absorptive activity of the gut may be influ enced by dietary factors and by the control of microbial flora through the use of antibiotics and probiotics. Even small changes in the efficiency with which energy is used by animals can have profound effects on animal productivity. Recently, researchers have learned that visceral tissues, especially the gastrointestinal tract and liver, have a disproportionately high rate of energy use compared to most other tissues. Understanding the factors that influence energy use by these visceral tis sues may enable us to control these processes and thus control the efficiency of animal production. A discus sion of changes in liver and gastrointestinal tract energy demands in response to physiological workload is pre sented by Johnson et al. (3).

Effects of deprivation of oxygen and glucose on the neural activity and the level of high energy phosphates in the hippocampal slices of immature and adult rat

To investigate neural activity and cerebral energy metabolism during anoxia in neural tissue of different ages, hippocampal slices were prepared from 4-, 7- and 10-day-old, and adult rats. Using these slices, the postsynaptic potential (psp) was recorded in the pyramidal cell layer of the CA1 area. Adenosine triphosphate (ATP), phosphocreatine (PCr) and lactate levels in the slices were measured during oxygen and glucose deprivation. The level of oxygen consumption was also measured for each slice in its resting state. After the onset of oxygen and glucose deprivation, the psp of slices from 4-, 7- and 10-day-old, and adult rats ceased completely in 22, 9, 5.6 and 4.6 min, respectively. Using initial changes in the levels of ATP, PCr and lactate during deprivation, the energy use rates of respective slices were calculated to be 1.09 ≈P mmol/g DNA/min in 4-day-old, 2.93 in 7-day-old, 3.42 in 10-day-old and 4.75 in adult rats. The oxygen consumption rates at rest for slices taken from 4-, 7- and 10-day-old, and adult rats were 0.13, 0.24, 0.47 and 0.80 ≈O 2 mmol/g DNA/min, respectively. Thus, differences in rates of energy use and oxygen consumption between immature and adult brain tissues correlated well with those of psp decay time during oxygen and glucose deprivation. The levels of ATP at the time of psp cessation in 4-, 7- and 10-day-old and adult brain slices were <23, 39, 51 and 61% of the initial value, respectively. This seems to indicate that in immature rats the functional store of ATP for neural activity is larger than it is in adult rats. This may partly explain why the brain tissue of immature rats was more resistant to both anoxia and ischemia, in addition to difference of energy use rate between immature and mature brain as mentioned above.

Use of glycolytic energy sources by human skeletal muscle under anoxic conditions in vitro and during moderate exercise in vivo.

To test a new in vitro model for investigations of muscle metabolism, the most important metabolites of muscle anaerobic metabolism (ATP, creatine phosphate, glucose, glycogen, and lactate) were measured in muscle biopsies from healthy male subjects, endurance-trained cyclists, strength-trained weight lifters, intensively trained long-distance runners, and speed-trained sprinters. The samples were taken at rest and after moderate muscle exercise for 30 s. These samples were analysed as such or after in vitro incubation for 30 s, 60 s, and 5 min under anoxic conditions. Anoxic conditions were created by incubating the muscle specimens in mineral oil through which N2 was bubbled. Under anoxic conditions in vitro, the concentrations of glycogen fell significantly in muscle specimens from sprinters and long-distance runners. The same tendency was observed in all other groups. The concentrations of high-energy phosphates. ATP and creatine phosphate, did not deplete under anoxic conditions. Under anoxic conditions, the rate of energy use, i.e., the metabolic rate calculated from the changes in the energy sources in terms of high-energy phosphate (P) use, was highest during the first 30 s, and declined to zero after 60 s. In the endurance-trained cyclists the metabolic rate was significantly lower than in any other group. In conclusion, muscle tissue behaves in quite a different way under anoxic conditions in vitro as compared with its behavior during exercise in vivo, and so the in vitro model is not suitable to compensate for studies of muscle metabolism in vivo. The in vitro model is of value, however, in, for example, determining the maximal metabolic rate of muscle.

Body size, ecological dominance and Cope's rule

We present data and analyses demonstrating that large species utilize a disproportionately large share of the resources within local ecosystems. Even though small species tend to have higher local population densities, these are not sufficient to compensate for their lower rates of energy use per individual. The relationship is very general; holding for example for birds, mammals, fish and plants. We suggest that several ecological advantages enable larger species and larger individuals within species to monopolize resources, and that the resulting selection pressures are responsible for the evolutionary trend towards increasing body size seen in many phyletic lineages. Our results contradict important studies1–4 that have concluded that species of small body size use at least as large a proportion of the resources within ecosystems as their larger relatives.

The efficiencies of the component steps of oxidative phosphorylation: II. Experimental determination of the efficiencies in mitochondria and examination of the equivalence of membrane potential and pH gradient in phosphorylation

In the accompanying article (T. E. Gunter and B. D. Jensen, 1986 Arch. Biochem. Biophys. 248, 289–304) , a method is described for measuring the efficiencies of individual steps of the process of oxidative phosphorylation. The results of applying this method to the case of state 3 phosphorylation in rat liver mitochondria are reported here. The rate of energy use (or power use) at the gradient generation, leakage, and phosphorylation steps are reported as efficiencies and energy use factors in tabular form. The limits of the degrees of coupling of the gradient generation and phosphorylation steps are also determined and under the current conditions of measurement these degrees of coupling are found to be quite close to unity. The data can be used to show that the only sets of the stoichiometric parameters n H O (the charge/2 e − ratio in this case from succinate to oxygen), n H P (the H + ATP ratio), and n H T (number of protons translocated during substrate-product transport) which are simultaneously consistent with both the laws of thermodynamics and with the current data are 8, 3, 1, and 6, 3, 0. The efficiency of the phosphorylation step which is independent of n H O and n H T averages 80% for the control data analyzed. If n H O is 8 (succinate to oxygen), the average value of the efficiency of generation of the electrochemical proton gradient is approximately 91 percent. Since very little power (energy) would then be left over to be coupled in parallel to phosphorylation through some other means of coupling, this would place the electrochemical proton gradient in the direct path of power flow and identify it as “an” intermediate in the process. This would suggest that any other intermediate should be considered as being “in series” with the electrochemical proton gradient. The agents butyrate and propionate have been employed to permit investigation over a range of pH gradient and membrane potential. Both butyrate and propionate decrease the efficiency of generation of the electrochemical proton gradient and increase proton leakage. In addition, butyrate activates electron transport whereas propionate inhibits it. By using butyrate to modify the values of pH gradient and membrane potential, it can be shown that the ratio of the efficiency with which the pH gradient is used in phosphorylation to that with which the membrane potential is used is 1.08 ± 0.38.

The just rate of depletion of a natural resource

The optimal pricing and use of a natural resource is reconsidered with respect to intergenerational equity considerations. It is assumed that in a just economy, each generation chooses the plan that maximizes its own utility, subject to the constraint that the plan should not be exploitative in the sense that each generation does not take advantage of its earlier point in time with respect to future generations. It is shown that if the cost of production of an alternative energy source (e.g., solar) is sufficiently high relative to the stock of naturally stored energy, the constraints of justice result in a lower rate of energy use initially, but a higher rate later.

Reducing Air Conditioning Waste by Signalling it is Cool Outside

This experiment looked at the effects on residential energy consumption of providing homeowners with (1) a signalling device that indicated a conservation opportunity and (2) information feedback about their rate of energy use. The signalling device operated when the outside temperature was below 680F and the air conditioner was on. Homeowners were told that the signalling device indicated when they could cool their house effectively by opening the windows and turning off their air conditioner. Forty households were randomly assigned to one of four conditions: signalling device only, feedback only, both, neither. The results showed a significant 15.7% decrease in energy use for those households with the signalling devices. Neither the feedback nor interaction effect was significant. The advantages and disadvantages of having people in the control cycle were discussed.

On the limits to energy growth

Although the total rate at which energy is released into the environment by man is only a fraction of one per cent as large as the heat absorbed from solar radiation, the continued escalation of energy use could cause global thermal pollution in a surprising short time. If the rate of energy use continues to increase as it has over the past ten years, serious climatic changes could result before the end of this century.

Cerebral energy reserves and glycolysis in neural tissue of 6-aminonicotinamide-treated mice.

AbstractCerebral energy metabolism was studied in brains of mice treated with the nicotinamide analog, 6‐aminonicotinamide (6‐AN), which is converted to a potent inhibitor of 6‐phosphogluconate dehydrogenase in viro. Six hours after administration of 6‐AN, the level of cerebral 6‐phosphogluconate was increased at least 170‐fold, whereas substrates for other NADP +‐dependent dehydrogenases either did not change or increased only slightly. Large increases in 6‐phosphogluconate were observed in the cerebral cortex, three layers of the cerebellum, and the dorsal column and anterior horn regions of the spinal cord after administration of 6‐AN. Thus, glucose was metabolized via the oxidative enrymes of the pentose phosphate pathway in a wide variety of neuronal structures in vivo. Highest concentrations of 6‐phosphogluconate were observed in the cerebellar molecular layer.Energy use rates and glycolysis were studied by measuring the disappearance of the major energy reserves during periods of anoxic‐ischemia imposed on cerebral tissue of 6‐AN‐treated mice. Production of lactate and utilization of glycogen during anoxic‐ischemia were reduced in brain of 6‐AN‐treated mice, which is in accord with the suggestion that glycolysis is inhibited in cerebral tissue of 6‐AN‐treated animals. Levels and ratios of pyridine nucleotides in cerebral tissue were not altered by 6‐AN treatment. From changes in levels of ATP, phosphocreatine, glucose, and glycogen in brain during ischemia, the rate of energy use was calculated to be 21.7 mmol · kg wet tissue−1 · min−1, which was not significantly different from that observed in normal adult mouse brain. Therefore, despite an apparent slowing of hexose utilization in cerebral tissue 6‐AN‐treated mice, normal cerebral energy use was maintained during the initial period of anoxic‐ischemia.

Effect of ischemia and denervation on metabolism of fast and slow mammalian skeletal muscle

Changes in major energy reserves, lactate and inorganic phosphate, were followed in innervated and denervated extensor digitorum longus and soleus muscles of the rat during ischemia. In the innervated muscles levels of energy reserves were higher in extensor than in soleus muscles. After denervation energy stores were significantly decreased in both types of muscle. During ischemia, the pattern of recruitment of energy reserves was similar in innervated and denervated muscles; however, ATP levels decreased most rapidly in extensor muscles denervated 5 days previously. Phosphocreatine decreased rapidly in all muscles during ischemia; glycogen, glucose, and ATP fell more slowly while glucose-6-P increased. From these changes, the initial rates of energy use during ischemia were calculated to be 12.4 and 11.2 mmoles/kg wet tissue per minute in innervated extensor and soleus muscles, respectively. Five days after denervation energy use rates decreased to 64 and 52% of control values in extensor and soleus muscles, respectively. Initial rates of lactate accumulation were slower in innervated than denervated muscles; however, glycogen and glucose were utilized at faster rates in innervated muscles. In view of these findings, it is concluded that reduction of metabolic rate is the chief factor involved in the decrease of high energy phosphate in both fast and slow denervated muscle.