Effect of reproduction on escape responses and muscle metabolic capacities in the scallop Chlamys islandica Müller 1776

In scallops, gametogenesis leads to mobilization of glycogen and proteins from the adductor muscle towards the gonad. This mobilization is likely to diminish the metabolic capacities of the adductor muscle and thereby the scallops' escape response. We examined the escape response in terms of number of valve claps until exhaustion, rate of clapping and the recovery during and after valve closure in adult scallops, Chlamys islandica, sampled at different stages in the reproductive cycle (immature, mature, before and after spawning). In parallel, we measured muscle glycogen, protein and phosphoarginine contents, the oxidative capacity of mitochondria isolated from the adductor muscle and levels of muscle enzymes which are active during exercise and recovery. The number of claps (24-26), rate of clapping ( approximately 13 clapsmin(-1)) and phosphoarginine and arginine kinase levels were similar during the different reproductive stages. All immature scallops responded to restimulation immediately after opening their valves, while only 62% of mature, 82% of prespawned and 38% of spawned scallops responded. Immature animals completely recovered their initial swimming capacity within 4 h of opening their valves, but mature, prespawned and spawned scallops needed 18, 12 and 18 h, respectively. Overall phasic adductor muscle from mature, prespawned and spawned animals showed decreased glycogen phosphorylase, phosphofructokinase, pyruvate kinase (except for prespawned), octopine dehydrogenase and citrate synthase levels, a deterioration of the oxidative capacity of mitochondria and a marked decrease in glycogen content compared to immature scallops. Therefore, during gonadal maturation and spawning, C. islandica did not change its clapping capacity, but slowed its recuperation from exhausting burst exercise, both during and after valve closure, likely due to the decreased metabolic capacity of the adductor muscle.     

Locomotor performance and muscle metabolic capacities: impact of temperature and energetic status

In aquatic ectotherms, muscle metabolic capacities are strongly influenced by exogenous factors, principally temperature and food availability. Seasonal changes in temperature lead many organisms to modify their metabolic machinery so as to maintain capacity even in "slower" cold habitats. Modifications of mitochondrial capacities are central in this response. The increases in protein-specific oxidative capacities of mitochondria during cold acclimation of temperate fishes do not occur during the evolutionary adaptation to cold in Antarctic species. Instead, Antarctic fishes tend to increase the proportion of fibre volume devoted to mitochondria, perhaps to facilitate intracellular distribution of oxygen and metabolites. Variation in energetic status can drastically modify muscle metabolic status, with glycolytic muscle changing more than oxidative muscle. This in turn impacts swimming performance. A decrease in the condition of cod leads endurance at speeds above Ucrit to drop by 70%. Sprint swimming is less affected, perhaps as it does not exhaust glycolytic muscle. We used interindividual variation in muscle metabolic capacities to identify correlates of swimming performance in stickleback and cod. Activities of cytochrome c oxidase in glycolytic muscle are a correlate of sprint swimming in stickleback (Gasterosteus aculeatus) and cod (Gadus morhua), whereas lactate dehydrogenase activities in glycolytic muscle are a correlate of cod endurance swimming. In scallops, gonadal maturation leads to virtually complete mobilisation of glycogen from muscle. This does not reduce the capacity of the scallops, Chlamys islandica and Euvola ziczac, to mount escape responses, but significantly slows their recuperation from exhaustive exercise. Muscle metabolic capacities fall in parallel with glycogen mobilisation. In the compromise between muscles' dual roles as a motor and a macromolecular reserve, a significant loss in locomotory ability occurs during gametogenesis and spawning. Reproductive fitness takes the upper hand over maintenance of performance.     

Metabolic and physiological responses in tissues of the long-lived bivalve Arctica islandica to oxygen deficiency

In Arctica islandica, a long lifespan is associated with low metabolic activity, and with a pronounced tolerance to low environmental oxygen. In order to study metabolic and physiological responses to low oxygen conditions vs. no oxygen in mantle, gill, adductor muscle and hemocytes of the ocean quahog, specimens from the German Bight were maintained for 3.5 days under normoxia (21 kPa=controls), hypoxia (2 kPa) or anoxia (0 kPa). Tissue levels of anaerobic metabolites octopine, lactate and succinate as well as specific activities of octopine dehydrogenase (ODH) and lactate dehydrogenase (LDH) were unaffected by hypoxic incubation, suggesting that the metabolism of A. islandica remains fully aerobic down to environmental oxygen levels of 2 kPa. PO(2)-dependent respiration rates of isolated gills indicated the onset of metabolic rate depression (MRD) below 5 kPa in A. islandica, while anaerobiosis was switched on in bivalve tissues only at anoxia. Tissue-specific levels of glutathione (GSH), a scavenger of reactive oxygen species (ROS), indicate no anticipatory antioxidant response takes place under experimental hypoxia and anoxia exposure. Highest specific ODH activity and a mean ODH/LDH ratio of 95 in the adductor muscle contrasted with maximal specific LDH activity and a mean ODH/LDH ratio of 0.3 in hemocytes. These differences in anaerobic enzyme activity patterns indicate that LDH and ODH play specific roles in different tissues of A. islandica which are likely to economize metabolism during anoxia and reoxygenation.     

Tonic contractions allow metabolic recuperation of the adductor muscle during escape responses of giant scallop Placopecten magellanicus

To escape from starfish predators, giant scallops, Placopecten magellanicus, swim using series of strong phasic contractions interrupted by tonic contractions. To investigate whether these tonic contractions allow metabolic recuperation of the adductor muscle, we sampled scallops at rest (Control), after an initial series of phasic contractions (Phasic) and after 1 min of tonic contraction following their initial phasic contractions (Phasic + Tonic) and compared muscle levels of phosphoarginine, adenylate nucleotides (ATP, ADP and AMP) and adenylate energy charge (AEC). Scallops in the two active groups did not differ in the numbers of phasic contractions or the mean phasic force production. Phosphoarginine concentrations in the adductor muscle decreased with phasic activity and remained low after 1 min of tonic contraction. ATP and ADP and total adenylate levels did not differ between the three groups, but AMP levels were higher in the scallops sampled after phasic contractions than in control scallops. The AEC was reduced by phasic contractions but returned to control levels after 1 min of tonic contraction. A significant negative correlation between AEC and the number of claps in the Phasic group disappeared in the Phasic + Tonic group. Thus, tonic contractions following phasic contractions allow partial metabolic recovery of the adductor muscle by returning AEC to control levels. However, phosphoarginine levels did not recover during tonic contractions, and a negative correlation between the number of claps and phosphoarginine levels remained in the Phasic + Tonic group. By interspersing tonic contractions between series of phasic contractions, scallops improved muscle energetic status, which should help maintain phasic force production during the remainder of the escape response.     

Modelling swimming activities and energetic costs in European sea bass (Dicentrarchus labrax L., 1758) during critical swimming tests

Muscular activity patterns in red and white muscles linked to oxygen consumption were studied during critical swimming tests in the sea bass (Dicentrarchus labrax Linnaeus 1758). The species is one of the most important for Mediterranean Sea aquaculture. A sigmoid model was used to fit both the oxygen consumption and red muscle activity while the white muscle activity pattern was described by an exponential model. Red muscle reaches an activation plateau close to critical swimming speed mostly due to the oxygen diffusion velocity in tissues. The exponential activation of white muscle appears to be linked to short and sudden periods of great energy need to cope with adverse conditions such as predation and escape. Both oxygen consumption and muscular activity were found to be size dependent. The bioenergetics of sea bass was modelled based on fish mass and swimming speed to predict the minimum and maximum speed as well as the mass-specific active metabolic rate and standard metabolic rate. An important finding was that contrary to other well-known species, swimming at subcritical speeds in sea bass involves both red and white muscle in different proportions.     

Comparative physiology of young and old cohorts of bay scallop Argopecten irradians irradians (Lamarck): mortality,growth, and oxygen consumption

The bay scallop Argopecten irradians (Lamarck) undergoes rapid population decline in its second year of life. Pre-(1st-yr) and postreproductive (2nd-yr) bay scallops were held in cages at two sites on Long Island, New York, U.S. Survival, growth, and metabolic rates of the two cohorts were compared monthly throughout the autumn and winter. Second-year scallops, the harvestable crop of the year, maintained a positive energy balance until late November–December. Both age classes experienced similar relative tissue weight losses during overwintering (9–11% at the site where milder environmental conditions prevailed, and 24–25% at the more stressful site). Ambient water temperature explained a significant proportion (93%) of the seasonal variation in the rate of oxygen consumption. Thus the northern bay scallop A.i. irradians shows a limited ability to acclimatise oxygen consumption to seasonal temperature changes over the range of 1–23°C. A significant increase in oxygen uptake was associated with increased gametogenic activity of young scallops in May. Metabolic rate at this time was 50% higher than that predicted based on temperature, providing an estimate of the metabolic cost of reproduction in this species. The weight-normalized oxygen uptake rate of senescent scallops was significantly lower than that of young scallops. Mass natural mortality of the older cohort occurred during the winter, before the onset of a second gametogenesis; only 50% of the population survived beyond late January in 1985. Mortality was delayed by 2.5 months during a similar experiment conducted in 1986. Results of this study suggest that senescent mortality of New York bay scallop populations is not directly linked to the energy drain of a second reproductive event following overwintering stress.     

Domestication reduces the capacity to escape from predators

Phenotypic plasticity in response to variations in predatory pressure frequently occurs in wild populations, but it may be more evident and critical in species subjected to high exploitation rates and aquaculture. The Chilean scallop Argopecten purpuratus is becoming a domesticated species and the production of hatchery-reared scallops (closed environment), has implied the development of successive generations of individuals deprived of several stimuli normally present in their natural habitats (e.g. predators). We compared the escape capacities between wild and cultured A. purpuratus and also evaluated the effect of reproductive investment on the escape response capacities. Wild and cultured scallops, at different reproductive stages (maturing, mature and spawned), were stimulated to escape with the predatory sea star Meyenaster gelatinosus. We recorded: (1) the time to reaction, (2) the total number of claps, the duration of the clapping response and the clapping rate until exhaustion, (3) the time they spent closed after exhaustion, and (4) the proportion of claps recovered, the duration of the clapping response and the clapping rate after 20 min of recuperation. We found that wild A. purpuratus (1) reacted earlier when contacted by their natural predator, (2) escaped faster (greater clapping rates), (3) spent less time with their valves closed when exhausted, and (4) most of their escape capacities (i.e. claps number; clapping time; capacity of recuperation) were less affected by the energetic requirements imposed by gonad maturation and/or spawning than in cultured scallops. We considered that all these aspects of the escape response would make wild scallops less vulnerable to predation than cultured scallops, thus decreasing predation risk. Given the reduction of escape performance in cultured scallops, we suggest that this aspect should be considered for the success of culture-based restocking programs.     

Content and synthesis of glycolytic enzymes and creatine kinase in skeletal muscles and normal and dystrophic chickens

A number of workers have reported that avian muscular dystrophy causes alterations in the levels of certain enzyme activities in "fast-twitch" muscle fibers but has little effect on enzyme activities in "slow-twitch" muscle fibers. In the present work, the effects of this disease on the content and relative rates of synthesis of a number of glycolytic enzymes and the skeletal muscle-specific MM isoenzyme of creatine kinase in chicken muscles was investigated. It was shown that (i) the approximate 50% reductions in steady-state concentrations of three glycolytic enzymes (aldolase, enolase, and glyceraldehyde-3-P dehydrogenase) in dystrophic breast (fast-twitch) muscle result predominantly from decreases in relative rates of synthesis, rather than accelerations in relative rates of degradation, of these proteins in the diseased tissue; (ii) in contrast to the situation with the glycolytic enzymes, muscular dystrophy has only minor effects (25% or less) on the content and relative rate of synthesis of MM creatine kinase in breast muscle fibers; (iii) the muscular dystrophy-associated alterations in content and synthesis of the glycolytic enzymes in breast muscle fibers become apparent only during postembryonic maturation of this tissue; and (iv) as expected, muscular dystrophy has no significant effect on the content or relative rates of synthesis of glycolytic enzymes in slow-twitch lateral adductor muscles of the chicken. These results are discussed in terms of the apparent similarities between the effects of muscular dystrophy and surgical denervation on the protein synthetic programs expressed by mature fast-twitch muscle fibers.     

Once a fast cod, always a fast cod: maintenance of performance hierarchies despite changing food availability in cod (Gadus morhua)

To examine whether Atlantic cod maintain constant hierarchies of sprint speeds and muscle metabolic capacities under different feeding regimes, the physiological capacities of individual cod were followed through a starvation-feeding-starvation cycle. We examined sprint speeds and maximal enzyme activities in white-muscle biopsies at each period. We measured the glycolytic enzymes, phosphofructokinase (PFK) and lactate dehydrogenase (LDH), the mitochondrial enzyme, cytochrome C oxidase (CCO), and the biosynthetic enzyme, nucleotide diphosphate kinase (NDPK). Sprint speeds were measured in a laser diode/photocell-timed raceway. As expected, the feeding regime had a marked impact on the physiological capacities of cod, but the responses differed for sprint-swimming and muscle metabolic capacities. The different enzyme activities as well the condition index generally decreased during the first starvation, improved with feeding, and fell again during the second starvation. In contrast, sprint performance improved after feeding but did not fall with the second starvation. Although both the enzyme activities and the sprint speeds showed considerable interindividual variation, sprint speeds were not significantly correlated with the enzyme activities. The hierarchy of sprint performance of the cod was maintained, regardless of the preceding feeding regime, whereas those of muscle metabolic capacities were not.     

Flight muscle enzyme activities do not differ between pelagic and near-shore foraging seabird species

Common terns (Sterna hirundo), sooty terns (S. fuscata) and brown noddies (Anous stolidus) are phylogenetically related seabirds that differ in field activity levels and daily energy expenditure. To test whether muscle metabolic capacities co-evolve with activity levels and energy expenditure, we collected pectoral muscle biopsies from members of each species, and measured the activities of key enzymes in oxidative metabolism (citrate synthase, CS), anaerobic metabolism (lactate dehydrogenase, LDH), glycolysis (pyruvate kinase, PK), fatty acid oxidation (3-hydroxyacyl CoA dehydrogenase) and phosphocreatine hydrolysis (creatine phosphokinase, CPK). We hypothesized that temperate-breeding common terns would have higher enzyme activities than the two tropical species (sooty terns and brown noddies); consistent with the higher activity level of common terns. There were no differences in enzyme activities among adults of the three species. Common tern chicks within 2-3 days of flight had two-fold higher pyruvate kinase activity than adults, suggesting an increased glycolytic capacity in the chicks. Given the lack of difference among species at the enzymatic level, our results support the notion that behavior and whole organism performance can evolve considerably before there are detectable changes in underlying lower-level physiological/biochemical traits.     

Can phenotypic plasticity facilitate the geographic expansion of the tilapia Oreochromis mossambicus?

Climate influences the distribution of organisms because of the thermal sensitivity of biochemical processes. Animals may compensate for the effects of variable temperatures, and plastic responses may facilitate radiation into different climates. The tropical fish Oreochromis mossambicus has radiated into climates that were thought to be thermally unsuitable. Here, we test the hypothesis that thermal acclimation will extend the locomotory and metabolic performance range of O. mossambicus. Juvenile fish were acclimated to 14 degrees, 17 degrees, and 22 degrees C. We measured responses to acclimation at three levels of organization: whole-animal performance (sustained swimming and resting and recovery rates of oxygen consumption), mitochondrial oxygen consumption in caudal muscle, and metabolic enzyme activities in muscle and liver at 12 degrees, 14 degrees, 17 degrees, 22 degrees, and 26 degrees C. Thermal optima of sustained swimming performance (U(crit)) changed significantly with acclimation, but acclimation had no effect on either resting or recovery oxygen consumption. Fish compensated for cold temperatures by upregulating state 3 mitochondrial oxygen consumption and increasing activity of lactate dehydrogenase in the liver. The capacity for phenotypic plasticity in O. mossambicus means that the fish would not be limited by its locomotor performance or metabolic physiology to expand its range into cooler thermal environments from its current distribution.     

Effects of voluntary activity and genetic selection on muscle metabolic capacities in house mice Mus domesticus.

Selective breeding is an important tool in behavioral genetics and evolutionary physiology, but it has rarely been applied to the study of exercise physiology. We are using artificial selection for increased wheel-running behavior to study the correlated evolution of locomotor activity and physiological determinants of exercise capacity in house mice. We studied enzyme activities and their response to voluntary wheel running in mixed hindlimb muscles of mice from generation 14, at which time individuals from selected lines ran more than twice as many revolutions per day as those from control (unselected) lines. Beginning at weaning and for 8 wk, we housed mice from each of four replicate selected lines and four replicate control lines with access to wheels that were free to rotate (wheel-access group) or locked (sedentary group). Among sedentary animals, mice from selected lines did not exhibit a general increase in aerobic capacities: no mitochondrial [except pyruvate dehydrogenase (PDH)] or glycolytic enzyme activity was significantly (P < 0.05) higher than in control mice. Sedentary mice from the selected lines exhibited a trend for higher muscle aerobic capacities, as indicated by higher levels of mitochondrial (cytochrome-c oxidase, carnitine palmitoyltransferase, citrate synthase, and PDH) and glycolytic (hexokinase and phosphofructokinase) enzymes, with concomitant lower anaerobic capacities, as indicated by lactate dehydrogenase (especially in male mice). Consistent with previous studies of endurance training in rats via voluntary wheel running or forced treadmill exercise, cytochrome-c oxidase, citrate synthase, and carnitine palmitoyltransferase activity increased in the wheel-access groups for both genders; hexokinase also increased in both genders. Some enzymes showed gender-specific responses: PDH and lactate dehydrogenase increased in wheel-access male but not female mice, and glycogen phosphorylase decreased in female but not in male mice. Two-way analysis of covariance revealed significant interactions between line type and activity group; for several enzymes, activities showed greater changes in mice from selected lines, presumably because such mice ran more revolutions per day and at greater velocities. Thus genetic selection for increased voluntary wheel running did not reduce the capability of muscle aerobic capacity to respond to training.     

Fuel use in hawkmoth (Amphion floridensis) flight muscle: enzyme activities and flux rates

The fuels used by the hawkmoth Amphion floridensis to power flight are determined by nectar-feeding, with fed moths using primarily carbohydrate and unfed moths using primarily fat. To investigate the metabolic pathways underlying fuel-use flexibility in this species, we measured the maximal activities of several key metabolic enzymes in the flight muscle of fed and unfed individuals, for which metabolic rates and fuel utilization had been previously determined. Hexokinase (HK) and phosphofructokinase (PFK) occur at high activities and, during carbohydrate-fueled flight, are estimated to operate at fractional velocities comparable to those of exclusively carbohydrate-utilizing insects. Females exhibited higher glycolytic enzyme activities than did males, and males regulated PFK activity according to nectar feeding. Although beta-hydroxyacyl-CoA dehydrogenase (HOAD) was found at high activities, carnitine palmitoyl transferase (CPT) was not detectable, suggesting that fatty acids may be utilized via a carnitine-independent pathway during flight. Principal component analysis revealed a tendency for the activities of citrate synthase, HK, PFK, and HOAD to be positively correlated among individuals, as well as a lesser tendency for the activities of glycolytic vs. mitochondrial enzymes to be negatively correlated with each other. However, the principal components did not correlate with variation in either oxygen consumption rate or fuel use in vivo, suggesting that variation in enzyme concentration did not determine differences among individuals in metabolic performance during flight. J. Exp. Zool. 290:108-114, 2001.     

Maximum activities and effects of fructose bisphosphate on pyruvate kinase from muscles of vertebrates and invertebrates in relation to the control of glycolysis

1. Comparison of the maximum activities of pyruvate kinase with those of phosphofructokinase in a large number of muscles from invertebrates and vertebrates indicates that, in general, in any individual muscle, the activity of pyruvate kinase is only severalfold higher than that of phosphofructokinase. This is consistent with the suggestion, based on mass-action ratio data, that the pyruvate kinase reaction is non-equilibrium in muscle. However, the range of activities of pyruvate kinase in these muscles is considerably larger than that of phosphofructokinase. This difference almost disappears if the enzyme activities from muscles that are known to possess an anaerobic ;succinate pathway' are excluded. It is suggested that, in these muscles, phosphofructokinase provides glycolytic residues for both pyruvate kinase (i.e. glycolysis) and phosphoenolpyruvate carboxykinase (i.e. the succinate pathway). This is supported by a negative correlation between the activity ratio, pyruvate kinase/phosphofructokinase, and the activities of nucleoside diphosphokinase in these muscles, since high activities of nucleoside diphosphokinase are considered to indicate the presence of the succinate pathway. 2. The effect of fructose bisphosphate on the activities of pyruvate kinase from many different muscles was studied. The stimulatory effect of fructose bisphosphate appears to be lost whenever an efficient system for supply of oxygen to the muscles is developed (e.g. insects, squids, birds and mammals). This suggests that activation of pyruvate kinase is important in the co-ordinated regulation of glycolysis in anaerobic or hypoxic conditions, when the change in glycolytic flux during the transition from rest to activity needs to be large in order to provide sufficient energy for the contractile activity. However, lack of this effect in the anaerobic muscles of the birds and mammals suggests that another metabolic control may exist for avian and mammalian pyruvate kinase in these muscles.     

Maximal enzyme activities, and myoglobin and glutathione concentrations in heart, liver and skeletal muscle of the Northern Short-tailed shrew (Blarina brevicauda; Insectivora: Soricidae)

We measured the enzymes of glycolysis, Krebs Cycle, beta-oxidation and electron transport in the heart, liver and skeletal muscle of the Northern Short-tailed Shrew, Blarina brevicauda. Additionally, we measured the amount of myoglobin in skeletal and heart muscle as well as the concentration of glutathione in heart. The picture that emerges is of an aerobically well-endowed animal with constrained anaerobic capacity as indicated by small activities of glycolytic enzymes and creatine kinase. Lipid metabolism and amino acid transamination, as well as gluconeogenesis, are predominant in processing carbon resources and probably reflect the large contribution lipid and protein make to the diet of this carnivore. The citrate synthase activity is the largest of any reported value for vertebrate heart (250 U/g). The additional, very active cytochrome c oxidase activity (220 U/g) and large myoglobin concentrations (8 mg/g) in heart are clearly the underpinnings of the rapid metabolic rates reported for small insectivores. The potential for generation of reactive oxygen species must be great since the total glutathione concentration (165 mumol/g) is 300-fold greater in shrew hearts than in hearts of rats.     

Effects of light-emitting diodes on thermally-induced oxidative stress in the bay scallop Argopecten irradians

ABSTRACT

Water temperature is an important stressor that affects the physiological and biochemical responses of scallops. In this study, we investigated the effect of different light-emitting diodes (LEDs; red, green and blue) on oxidative stress in Argopecten irradians. PCR revealed MnSOD mRNA expression in the digestive diverticula, gill, adductor muscle and eye. CAT and HSP70 mRNA were expressed in the digestive diverticula, gill and adductor muscle. Additionally, we measured the changes in the expression of HSP70, MnSOD and CAT as well as H₂O₂ levels during thermal/laboratory stress. In the digestive diverticula, gill and adductor muscle, the mRNA expressions and activities and H₂O₂ levels significantly increased in response to thermal changes. The gene expressions and activities and H₂O₂ levels were significantly lower in scallops that received green LED light than in those that received no mitigating treatment. A comet assay revealed that thermal change groups had increased rates of nuclear DNA damage; however, treatment with green LED reduced the frequency of damage. The results indicated that low or high water temperature conditions induced oxidative stress in A. irradians but that green LED significantly reduced this stress.     

Adaptations in metabolic capacity of rat soleus after paralysis.

To determine whether long-term reductions in neuromuscular activity result in alterations in metabolic capacity, the activities of oxidative, i.e., succinate dehydrogenase (SDH) and citrate synthase (CS), and glycolytic, i.e., alpha-glycerophosphate dehydrogenase (GPD), enzyme markers were quantified in rat soleus muscles 1, 3, and 6 mo after a complete spinal cord transection (ST). In addition, the proportional content of lactate dehydrogenase (LDH) isozymes was used as a marker for oxidative and glycolytic capacities. The myosin heavy chain (MHC) isoform content of a fiber served as a marker of phenotype. In general, MHC isoforms shifted from MHC1 toward MHC2, particularly MHC2x, after ST. Mean SDH and CS activities were higher in ST than control at all time points. The elevated SDH and CS activities were indicative of an enhanced oxidative capacity. GPD activities were higher in ST than control rats at all time points. The increase in activity of SDH was larger than GPD. Thus the GPD-to-SDH (glycolytic-to-oxidative) ratio was decreased after ST. Compared with controls, total LDH activity increased transiently, and the LDH isozyme profile shifted from LDH-1 toward LDH-5, indicative of an enhanced glycolytic capacity. Combined, these results indicate that 1) the metabolic capacities of soleus fibers were not compromised, but the interrelationships among oxidative and glycolytic capacity and MHC content were apparently dissociated after ST; 2) enhancements in oxidative and glycolytic enzyme activities are not mutually exclusive; and 3) chronic reductions in skeletal muscle activity do not necessarily result in a reduced oxidative capacity.     

Protein profiles in human ovarian cancer cell lines correspond to their metabolic activity and to metabolic profiles of respective tumor xenografts

Many solid tumors show a large variability in glycolytic activity and lactate accumulation, which has been correlated with different metastatic spread, radioresistance and patient survival. To investigate potential differences in protein profiles underlying these metabolic variances, the highly glycolytic human ovarian cancer cell line OC316 was investigated and compared with the less glycolytic line IGROV-1. Extracellular acidification and oxygen consumption were analyzed with an extracellular flux analyzer. Glycolysis-associated proteins, including specific membrane transporters, were quantified through in-cell western analyses. Metabolic properties of corresponding tumor xenografts were assessed via induced metabolic bioluminescence imaging. Extracellular flux analyses revealed elevated bioenergetics of OC316 cells. Hexokinase II, pyruvate kinase, pyruvate dehydrogenase E1 beta subunit and pyruvate dehydrogenase kinase 1, as well as the glucose transporter 1 and the monocarboxylate transporter 4, were overexpressed in these cells compared with IGROV-1. When generating tumor xenografts in SCID mice, cells maintained their glycolytic behavior, i.e. OC316 showed higher lactate concentrations than IGROV-1 tumors. In summary, a congruency between protein profiles and metabolic properties has been demonstrated in the human ovarian cancer lines investigated. Also, a perpetuation of glycolytic characteristics during the transition from in vitro to the in vivo situation has been documented. This model system could be useful for systematic studies on therapeutic intervention by manipulation of tumor glycolysis and associated pathways.     

Regulation of concentrations of glycolytic enzymes and creatine-phosphate kinase in “fast-twitch” and “slow-twitch” skeletal muscles of the chicken

The distinctive contractile and metabolic characteristics of different skeletal muscle fiber types are associated with different protein populations in these cells. In the present work, we investigate the regulation of concentrations of three glycolytic enzymes (aldolase, enolase, glyceraldehyde-3-phosphate dehydrogenase) and creatine-phosphate kinase in “fast-twitch” (breast) and “slow-twitch” (lateral adductor) muscles of the chicken. Results of short-term amino acid incorporation experiments conducted both in vivo and with muscle explants in vitro showed that these enzymes turnover at different rates and that aldolase turns over 2 to 3 times faster than the other three enzymes. However, these differences in turnover rates were difficult to detect in long-term double-isotope incorporation experiments, presumably because extensive reutilization of labeled amino acids occurred during these long-term experiments. Mature muscle fibers synthesize these four cytosolic enzymes at very high rates. For example, 11 to 14% of the total labeled leucine incorporated into protein by breast muscle fibers was found in the enzyme aldolase. Results of short-term amino acid incorporation experiments also showed that the relative rates of synthesis of the three glycolytic enzymes were about fourfold higher in mature “fast-twitch” muscle fibers than in mature “slow-twitch” ones while the relative rates of synthesis of creatine-phosphate kinase were similar in the two fiber types. The relative rates of synthesis of these four enzymes and cytosolic proteins in general were found to be very similar in immature muscles of both types. More profound changes in the relative rates of synthesis of major cytosolic proteins, including the glycolytic enzymes, occurred during postembryonic maturation of fast-twitch fibers than occurred during maturation of slow-twitch fibers. Our work demonstrates that (1) the synthesis of creatine-phosphate is independently regulated with respect to the synthesis of the glycolytic enzymes in muscle fibers; and (2) the approximate fourfold higher steady-state concentrations of glycolytic enzymes in fast-twitch muscle fibers as compared with slow-twitch fibers are determined predominantly by regulatory mechanisms operating at the level of protein synthesis rather than protein degradation. Our demonstration that more profound changes in the relative rates of synthesis of major cytosolic proteins occur during maturation of fast-twitch fibers as compared with slow-twitch fibers is discussed in terms of the mode(s) of fiber-type differentiation proposed by others.