Oxidative properties of carp red and white muscle

Respiratory substrate preferences in mitochondria isolated from different tissues of three fish species

Energy requirements of tissues vary greatly and exhibit different mitochondrial respiratory activities with variable participation of both substrates and oxidative phosphorylation. The present study aimed to (1) compare the substrate preferences of mitochondria from different tissues and fish species with different ecological characteristics, (2) identify an appropriate substrate for comparing metabolism by mitochondria from different tissues and species, and (3) explore the relationship between mitochondrial metabolism mechanisms and ecological energetic strategies. Respiration rates and cytochrome c oxidase (CCO) activities of mitochondria isolated from heart, brain, kidney, and other tissues from Silurus meridionalis, Carassius auratus, and Megalobrama amblycephala were measured using succinate (complex II-linked substrate), pyruvate (complex I-linked), glutamate (complex I-linked), or combinations. Mitochondria from all tissues and species exhibited substrate preferences. Mitochondria exhibited greater coupling efficiencies and lower leakage rates using either complex I-linked substrates, whereas an opposite trend was observed for succinate (complex II-linked). Furthermore, maximum mitochondrial respiration rates were higher with the substrate combinations than with individual substrates; therefore, state III respiration rates measured with substrate combinations could be effective indicators of maximum mitochondrial metabolic capacity. Regardless of fish species, both state III respiration rates and CCO activities were the highest in heart mitochondria, followed by red muscle mitochondria. However, differences in substrate preferences were not associated with species feeding habit. The maximum respiration rates of heart mitochondria with substrate combinations could indicate differences in locomotor performances, with higher metabolic rates being associated with greater capacity for sustained swimming.

Metabolic consequences of PGC-1α dysregulation in adult zebrafish muscle

The peroxisome proliferator activated receptor gamma co-activator 1 alpha (PGC-1α) is central to the regulation of cellular and mitochondrial energy homeostasis in mammals, but its role in other vertebrates remains unclear. Indeed, previous work suggests extensive structural and functional divergence of PGC-1α in teleosts but this remains to be directly tested. Here, we describe the initial characterization of heterozygous PGC-1α mutant zebrafish lines created by CRISPR-Cas9 disruptions of an evolutionarily conserved regulatory region of the PGC-1α proximal promoter. Using qPCR, we confirmed the disruption of PGC-1α gene expression in striated muscle, leading to a simultaneous 4-fold increase in mixed skeletal muscle PGC-1α mRNA levels and an opposite 4-fold downregulation in cardiac muscle. In mixed skeletal muscle, most downstream effector genes were largely unaffected yet two mitochondrial lipid transporters, carnitine palmitoyltransferase 1 and 2, were strongly induced. Conversely, PGC-1α depression in cardiac muscle reduced the expression of several transcriptional regulators (estrogen related receptor alpha, nuclear respiratory factor 1 and PGC-1β) without altering metabolic gene expression. Using high resolution respirometry, we determined that white muscle exhibited increased lipid oxidative capacity with little difference in markers of mitochondrial abundance. Finally, using whole animal intermittent respirometry, we show that mutant fish exhibit a 2-fold higher basal metabolism than their wildtype counterparts. Altogether, this new model confirms a central but complex role for PGC-1α in mediating energy utilization in zebrafish and we propose its use as a valuable tool to explore the intricate regulatory pathways of energy homeostasis in a popular biomedical model.

Review: Using isolated mitochondria to investigate mitochondrial hydrogen peroxide metabolism

Mitochondria are recognized as centrally important to cellular reactive oxygen species (ROS), both as a potential source and due to their substantial antioxidant capacity. While much of the initial ROS formed by mitochondria is superoxide, this is rapidly converted to hydrogen peroxide (H₂O₂) which more readily crosses membranes making H₂O₂ important in both redox signalling mechanisms and conditions of oxidative stress. Here I outline our studies on mitochondrial H₂O₂ metabolism with a focus on some of the challenges and strategies involved with developing an integrated model of mitochondria being intrinsic regulators of H₂O₂. This view of mitochondria as regulators of H₂O₂ goes beyond the simpler contention of them being net producers or consumers. Moreover, the integration of both consumption and production can then be tied to a putative mechanism linking energy sensing at the level of the mitochondrial protonmotive force. This mechanism would provide a means of mitochondria communicating their energetic status the extramitochondrial compartment via local H₂O₂ concentrations. I conclude by explaining how these concepts developed using rodent muscle as a model have high relevance and applicability to comparative studies.

Comparison of Mitochondrial Reactive Oxygen Species Production of Ectothermic and Endothermic Fish Muscle

Recently we demonstrated that the capacity of isolated muscle mitochondria to produce reactive oxygen species, measured as H₂O₂ efflux, is temperature-sensitive in isolated muscle mitochondria of ectothermic fish and the rat, a representative endothermic mammal. However, at physiological temperatures (15° and 37°C for the fish and rat, respectively), the fraction of total mitochondrial electron flux that generated H₂O₂, the fractional electron leak (FEL), was far lower in the rat than in fish. Those results suggested that the elevated body temperatures associated with endothermy may lead to a compensatory decrease in mitochondrial ROS production relative to respiratory capacity. To test this hypothesis we compare slow twitch (red) muscle mitochondria from the endothermic Pacific bluefin tuna (Thunnus orientalis) with mitochondria from three ectothermic fishes [rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio), and the lake sturgeon (Acipenser fulvescens)] and the rat. At a common assay temperature (25°C) rates of mitochondrial respiration and H₂O₂ efflux were similar in tuna and the other fishes. The thermal sensitivity of fish mitochondria was similar irrespective of ectothermy or endothermy. Comparing tuna to the rat at a common temperature, respiration rates were similar, or lower depending on mitochondrial substrates. FEL was not different across fish species at a common assay temperature (25°C) but was markedly higher in fishes than in rat. Overall, endothermy and warming of Pacific Bluefin tuna red muscle may increase the potential for ROS production by muscle mitochondria but the evolution of endothermy in this species is not necessarily associated with a compensatory reduction of ROS production relative to the respiratory capacity of mitochondria.

Products of lipid peroxidation, but not membrane susceptibility to oxidative damage, are conserved in skeletal muscle following temperature acclimation

Changes in oxidative capacities and phospholipid remodeling accompany temperature acclimation in ectothermic animals. Both responses may alter redox status and membrane susceptibility to lipid peroxidation (LPO). We tested the hypothesis that phospholipid remodeling is sufficient to offset temperature-driven rates of LPO and, thus, membrane susceptibility to LPO is conserved. We also predicted that the content of LPO products is maintained over a range of physiological temperatures. To assess LPO susceptibility, rates of LPO were quantified with the fluorescent probe C11-BODIPY in mitochondria and sarcoplasmic reticulum from oxidative and glycolytic muscle of striped bass (Morone saxatilis) acclimated to 7°C and 25°C. We also measured phospholipid compositions, contents of LPO products [i.e., individual classes of phospholipid hydroperoxides (PLOOH)], and two membrane antioxidants. Despite phospholipid headgroup and acyl chain remodeling, these alterations do not counter the effect of temperature on LPO rates (i.e., LPO rates are generally not different among acclimation groups when normalized to phospholipid content and compared at a common temperature). Although absolute levels of PLOOH are higher in muscles from cold- than warm-acclimated fish, this difference is lost when PLOOH levels are normalized to total phospholipid. Contents of vitamin E and two homologs of ubiquinone are more than four times higher in mitochondria prepared from oxidative muscle of warm- than cold-acclimated fish. Collectively, our data demonstrate that although phospholipid remodeling does not provide a means for offsetting thermal effects on rates of LPO, differences in phospholipid quantity ensure a constant proportion of LPO products with temperature variation.

Effect of body size on organ-specific mitochondrial respiration rate of the largemouth bronze gudgeon

The effects of body size on the mitochondrial respiration rate were assessed in the heart, brain, gill, liver, and red muscle of largemouth bronze gudgeon, Coreius guichenoti, from the Yangtze River. Body mass had a significant influence on the state 3 oxygen consumption rate of the mitochondria from the heart, gill, and red muscle. The relationships between body mass (M, g) and state 3 oxygen consumption rate (V(state 3), nmol O min(-1) mg(-1)) of the mitochondria were represented by the following: V(state 3) = 3.56M(0.71) for heart, V(state 3) = 4.64M(0.50) for red muscle, and V(state 3) = 473.73M(-0.82) for gill. There was a significant difference in V(state 3), V(state 4), and respiratory control ratio among organs and all were highest in the heart. Our results suggest that the relationship between mitochondrial respiratory rate and body size varies among organs. The high mitochondrial respiratory rate in the heart of the largemouth gudgeon suggests that it has the highest oxidative capacity.

Zebrafish: a model animal for analyzing the impact of environmental pollutants on muscle and brain mitochondrial bioenergetics

Mercury, anthropogenic release of uranium (U), and nanoparticles constitute hazardous environmental pollutants able to accumulate along the aquatic food chain with severe risk for animal and human health. The impact of such pollutants on living organisms has been up to now approached by classical toxicology in which huge doses of toxic compounds, environmentally irrelevant, are displayed through routes that never occur in the lifespan of organisms (for instance injecting a bolus of mercury to an animal although the main route is through prey and fish eating). We wanted to address the effect of such pollutants on the muscle and brain mitochondrial bioenergetics under realistic conditions, at unprecedented low doses, using an aquatic model animal, the zebrafish Danio rerio. We developed an original method to measure brain mitochondrial respiration: a single brain was put in 1.5 mL conical tube containing a respiratory buffer. Brains were gently homogenized by 13 strokes with a conical plastic pestle, and the homogenates were immediately used for respiration measurements. Skinned muscle fibers were prepared by saponin permeabilization. Zebrafish were contaminated with food containing 13 μg of methylmercury (MeHg)/g, an environmentally relevant dose. In permeabilized muscle fibers, we observed a strong inhibition of both state 3 mitochondrial respiration and cytochrome c oxidase activity after 49 days of MeHg exposure. We measured a dramatic decrease in the rate of ATP release by skinned muscle fibers. Contrarily to muscles, brain mitochondrial respiration was not modified by MeHg exposure although brain accumulated twice as much MeHg than muscles. When zebrafish were exposed to 30 μg/L of waterborne U, the basal mitochondrial respiratory control ratio was decreased in muscles after 28 days of exposure. This was due to an increase of the inner mitochondrial membrane permeability. The impact of a daily ration of food containing gold nanoparticles of two sizes (12 and 50 nm) was investigated at a very low dose for 60 days (40 ng gold/fish/day). Mitochondrial dysfunctions appeared in brain and muscle for both tested sizes. In conclusion, at low environmental doses, dietary or waterborne heavy metals impinged on zebrafish tissue mitochondrial respiration. Due to its incredible simplicity avoiding tedious and time-consuming mitochondria isolation, our one-pot method allowing brain respiratory analysis should give colleagues the incentive to use zebrafish brain as a model in bioenergetics. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

The metabolic effects of prolonged starvation and refeeding in sturgeon and rainbow trout

The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts.

Scaling with body mass of mitochondrial respiration from the white muscle of three phylogenetically, morphologically and behaviorally disparate teleost fishes

White muscle (WM) fibers in many fishes often increase in size from <50 μm in juveniles to >250 μm in adults. This leads to increases in intracellular diffusion distances that may impact the scaling with body mass of muscle metabolism. We have previously found similar negative scaling of aerobic capacity (mitochondrial volume density, V(mt)) and the rate of an aerobic process (post-contractile phosphocreatine recovery) in fish WM. In the present study, we examined the scaling with body mass of oxygen consumption rates of isolated mitochondria (VO(2mt)) from WM in three species from different families that vary in morphology and behavior: an active, pelagic species (bluefish, Pomatomus saltatrix), a relatively inactive demersal species (black sea bass, Centropristis striata), and a sedentary, benthic species (southern flounder, Paralichthys lethostigma). In contrast to our prior studies, the measurement of respiration in isolated mitochondria is not influenced by the diffusion of oxygen or metabolites. V(mt) was measured in WM and in high-density isolates used for VO(2mt) measurements. WM V(mt) was significantly higher in the bluefish than in the other two species and VO(2mt) was independent of body mass when expressed per milligram protein or per milliliter mitochondria. The size-independence of VO(2mt) indicates that differences in WM aerobic function result from variation in V(mt) and not to changes in VO(2mt). This is consistent with our prior work that indicated that while diffusion constraints influence mitochondrial distribution, the negative scaling of aerobic processes like post-contractile PCr recovery can largely be attributed to the body size dependence of V(mt).

Temperature acclimation alters oxidative capacities and composition of membrane lipids without influencing activities of enzymatic antioxidants or susceptibility to lipid peroxidation in fish muscle

Cold acclimation of ectotherms results typically in enhanced oxidative capacities and lipid remodeling, changes that should increase the risk of lipid peroxidation (LPO). It is unclear whether activities of antioxidant enzymes may respond in a manner to mitigate the increased potential for LPO. The current study addresses these questions using killifish (Fundulus heteroclitus macrolepidotus) and bluegill (Lepomis macrochirus) acclimated to 5 and 25 degrees C for 9 days and 2 months, respectively. Because the effects of temperature acclimation on pro- and antioxidant metabolism may be confounded by variable activity levels among temperature groups, one species (killifish) was also subjected to a 9-day exercise acclimation. Oxidative capacity of glycolytic (skeletal) muscle (indicated by the activity of cytochrome c oxidase) was elevated by 1.5-fold in killifish, following cold acclimation, but was unchanged in cardiac muscle and also unaffected by exercise acclimation in either tissue. No changes in citrate synthase activity were detected in either tissue following temperature acclimation. Enzymatic antioxidants (catalase and superoxide dismutase) of either muscle type were unaltered by temperature or exercise acclimation. Mitochondria from glycolytic muscle of cold-acclimated killifish were enriched in highly oxidizable polyunsaturated fatty acids (PUFA), including diacyl phospholipids (total carbons:total double bonds) 40:8 and 44:12. Increased oxidative capacity, coupled with elevated PUFA content in mitochondria from cold-acclimated animals did not, however, impact LPO susceptibility when measured with C11-BODIPY. The apparent mismatch between oxidative capacity and enzymatic antioxidants following temperature acclimation will be addressed in future studies.

The unusual energy metabolism of elasmobranch fishes

The unusual energy metabolism of elasmobranchs is characterized by limited or absent fatty acid oxidation in cardiac and skeletal muscle and a great reliance on ketone bodies and amino acids as oxidative fuels in these tissues. Other extrahepatic tissues in elasmobranchs rely on ketone bodies and amino acids for aerobic energy production but, unlike muscle, also appear to possess a significant capacity to oxidize fatty acids. This organization of energy metabolism is reflected by relatively low plasma levels of non-esterified fatty acids (NEFA) and by plasma levels of the ketone body ss-hydroxybutyrate that are as high as those seen in fasted mammals. The preference for ketone body oxidation rather than fatty acid oxidation in muscle of elasmobranchs under routine conditions is opposite to the situation in teleosts and mammals. Carbohydrates appear to be utilized as a fuel source in elasmobranchs, similar to other vertebrates. Amino acid- and lipid-fueled ketogenesis in the liver, the lipid storage site in elasmobranchs, sustains the demand for ketone bodies as oxidative fuels. The liver also appears to export NEFA and serves a buoyancy role. The regulation of energy metabolism in elasmobranchs and the effects of environmental factors remain poorly understood. The metabolic organization of elasmobranchs was likely present in the common ancestor of the Chondrichthyes ca. 400million years ago and, speculatively, it may reflect the ancestral metabolism of jawed vertebrates. We assess hypotheses for the evolution of the unusual energy metabolism of elasmobranchs and propose that the need to synthesize urea has influenced the utilization of ketone bodies and amino acids as oxidative fuels.

Metabolic organization of the spotted ratfish, Hydrolagus colliei (Holocephali: Chimaeriformes): insight into the evolution of energy metabolism in the chondrichthyan fishes

The metabolic organization of a holocephalan, the spotted ratfish (Hydrolagus colliei), was assessed using measurements of key enzymes of several metabolic pathways in four tissues and plasma concentrations of free amino acids (FAA) and non-esterified fatty acids (NEFA) to ascertain if the Holocephali differ metabolically from the Elasmobranchii since these groups diverged ca. 400 Mya. Activities of carnitine palmitoyl transferase indicate that fatty acid oxidation occurs in liver and kidney but not in heart or white muscle. This result mirrors the well-established absence of lipid oxidation in elasmobranch muscle, and more recent studies showing that elasmobranch kidney possesses a capacity for lipid oxidation. High activities in oxidative tissues of enzymes of ketone body metabolism, including D-beta-hydroxybutyrate dehydrogenase, indicate that, like elasmobranchs, ketone bodies are of central importance in spotted ratfish. Like many carnivorous fishes, enzyme activities demonstrate that amino acids are metabolically important, although the concentration of plasma FAA was relatively low. NEFA concentrations are lower than in teleosts, but higher than in most elasmobranchs and similar to that in some "primitive" ray-finned fishes. NEFA composition is comparable to other marine temperate fishes, including high levels of n-6 and especially n-3 polyunsaturated fatty acids. The metabolic organization of the spotted ratfish is similar to that of elasmobranchs: a reduced capacity for lipid oxidation in muscle, lower plasma NEFA levels, and an emphasis on ketone bodies as oxidative fuel. This metabolic strategy was likely present in the common chondrichthyan ancestor, and may be similar to the ancestral metabolic state of fishes.

The metabolic organization of a primitive air-breathing fish, the Florida gar (lepisosteus platyrhincus)

The metabolic organization of the air-breathing Florida gar, Lepisosteus platyrhincus, was assessed by measuring the maximal activities of key enzymes in several metabolic pathways in selected tissues, concentrations of plasma metabolites including nonesterified fatty acids (NEFA), free amino acids (FAA) and glucose as well as tissue FAA levels. In general, L. platyrhincus has an enhanced capacity for carbohydrate metabolism as indicated by elevated plasma glucose levels and high activities of gluconeogenic and glycolytic enzymes. Based upon these properties, glucose appears to function as the major fuel source in the Florida gar. The capacity for lipid metabolism in L. platyrhincus appears limited as plasma NEFA levels and the activities of enzymes involved in lipid oxidation are low relative to many other fish species. L. platyrhincus is capable of oxidizing both D- and L-beta-hydroxybutyrate, with tissue-specific preferences for each stereoisomer, yet the capacity for ketone body metabolism is low compared with other primitive fishes. Based on enzyme activities, the metabolism of the air-breathing organ more closely resembles that of the mammalian lung than a fish swim bladder. The Florida gar sits phylogenetically and metabolically in an intermediate position between the "primitive" elasmobranchs and the "advanced" teleosts. The apparently unique metabolic organization of the gar may have evolved in the context of a bimodal air-breathing environmental adaptation.

Fat to the fire: the regulation of lipid oxidation with exercise and environmental stress

Lipids are an important fuel for submaximal aerobic exercise. The ways in which lipid oxidation is regulated during locomotion is an area of active investigation. Indeed, the integration between cellular regulation of lipid metabolism and whole-body exercise performance is a fascinating but often overlooked research area. Additionally, the interaction between environmental stress, exercise, and lipid oxidation has not been sufficiently examined. There are many functional and structural steps as fatty acids are mobilized, transported, and oxidized in working muscle, which may serve either as regulatory points for responding to acute or chronic stimuli or as raw material for natural selection. At the whole-animal level, the partitioning of lipids and carbohydrates across exercise intensities is remarkably similar among mammals, which suggests that there is conservation in regulatory mechanisms. Conversely, the proportions of circulatory and intramuscular fuels differ between species and across exercise intensities. Responses to acute and chronic environmental stress likely involve the interaction of genetic and nongenetic changes in the fatty acid pathway. Determining which of these factors help regulate the fatty acid pathway and what impact they have on whole-animal lipid oxidation and performance is an important area of future research. Using an integrative approach to complete the information loop from gene to physiological function provides the most powerful mode of analysis.

Mitochondria: aerobic and anaerobic design--lessons from molluscs and fishes

The contributions of Peter Hochachka to the development of comparative and adaptational biochemistry are substantial. In particular, he and his academic offspring made major contributions to the understanding of the metabolism of molluscs and fishes. These two large taxonomic groups each have marine, freshwater and terrestrial/semiterrestrial representatives, and their mitochondrial metabolism has been shaped by these environmental conditions. In particular, the importance of amino acids and lipids as energy sources has interesting correlations with the environment and the osmotic strategy used. In marine molluscs, amino acids are important aerobic energy sources, and are used as osmolytes and participate in anaerobic metabolism. In marine elasmobranchs, amino acids and ketone bodies, but not lipids per se, are important energy sources in extrahepatic tissues. Marine and freshwater teleost fish by contrast use lipids as an extrahepatic energy source with minimal use of ketone bodies. Furthermore, ketone bodies are important in the metabolism of freshwater and terrestrial but not marine molluscs. The bases for these different metabolic plans may lie in the solute systems used by the different groups (e.g. amino acids in marine molluscs and urea in marine elasmobranchs). The various metabolic options used by fishes and molluscs indicate the plasticity of metabolic design in an environmental context.

PETER HOCHACHKA: Adventures in Biochemical Adaptation

Peter Hochachka was one of the most creative forces in the field of comparative physiology during the past half-century. His career was truly an exploratory adventure, in both intellectual and geographic senses. His broad comparative studies of metabolism in organisms as diverse as trout, tunas, oysters, squid, turtles, locusts, hummingbirds, seals, and humans revealed the adaptable features of enzymes and metabolic pathways that provide the biochemical bases for diverse lifestyles and environments. In its combined breadth and depth, no other corpus of work better illustrates the principle of "unity in diversity" that marks comparative physiology. Through his publications, his stimulating mentorship, his broad editorial services, and his continuous-and highly infectious-enthusiasm for his field, Peter Hochachka served as one of the most influential leaders in the transformation of comparative physiology.

Palmitate movement across red and white muscle membranes of rainbow trout

We examined the movement of [3H]palmitate across giant sarcolemmal vesicles prepared from red and white muscle of rainbow trout (Oncorhynchus mykiss). Red and white muscle fatty acid carriers have similar affinities for palmitate (apparent Km = 26 +/- 6 and 33 +/- 8 nM, respectively); however, red muscle has a higher maximal uptake compared with white muscle (Vmax = 476 +/- 41 vs. 229 +/- 23 pmol.mg protein-1.s-1, respectively). Phloretin (250 microM) inhibited palmitate influx in red and white muscle vesicles by approximately 40%, HgCl2 (2.5 mM) inhibited palmitate uptake by 20-30%, and the anion-exchange inhibitor DIDS (250 microM) inhibited palmitate influx in red and white muscle vesicles by approximately 15 and 30%, respectively. Western blot analysis of red and white muscle vesicles did not detect a mammalian-type fatty acid transporter (FAT); however, preincubation of vesicles with sulfo-N-succinimidyloleate, a specific inhibitor of FAT in rats, reduced palmitate uptake in red and white muscle vesicles by approximately 15 and 25%, respectively. A mammalian-type plasma membrane fatty acid-binding protein was identified in trout muscle using Western blotting, but the protein differed in size between red and white muscle. At low concentrations of free palmitate (2.5 nM), addition of high concentrations (111 microM total) of oleate (18:0) caused approximately 50% reduction in palmitate uptake by red and white muscle vesicles, but high concentrations (100 microM) of octanoate (8:0) caused no inhibition of uptake. Five days of aerobic swimming at approximately 2 body lengths/s and 9 days of chronic cortisol elevation in vivo, both of which stimulate lipid metabolism, had no effect on the rate of palmitate movement in red or white muscle vesicles.

Origins and consequences of mitochondrial variation in vertebrate muscle

This review addresses the mechanisms by which mitochondrial structure and function are regulated, with a focus on vertebrate muscle. We consider the adaptive remodeling that arises during physiological transitions such as differentiation, development, and contractile activity. Parallels are drawn between such phenotypic changes and the pattern of change arising over evolutionary time, as suggested by interspecies comparisons. We address the physiological and evolutionary relationships between ATP production, thermogenesis, and superoxide generation in the context of mitochondrial function. Our discussion of mitochondrial structure focuses on the regulation of membrane composition and maintenance of the three-dimensional reticulum. Current studies of mitochondrial biogenesis strive to integrate muscle functional parameters with signal transduction and molecular genetics, providing insight into the origins of variation arising between physiological states, fiber types, and species.

Cloning and tissue distribution of a carnitine palmitoyltransferase I gene in rainbow trout (Oncorhynchus mykiss)

The carnitine palmitoyltransferase I (EC.2.3.1.21; CPT I) mediates the transport of fatty acids across the outer mitochondrial membrane. In mammals, there are two different proteins CPT I in the skeletal muscle (M) and liver (L) encoded by two genes. The carnitine palmitoyltransferase system of lower vertebrates received little attention. With the aim of improving knowledge on the CPT family in fish, we examined CPT I cDNA and CPT activity in different tissues of rainbow trout (Oncorhynchus mykiss). Using RT-PCR, we successfully cloned a partial CPT I cDNA sequence (1650 bp). The predicted protein sequence revealed identities of 63% and 61% with human L-CPT I and M-CPT I, respectively. This mRNA is expressed in liver, white and red skeletal muscles, heart, intestine, kidney and adipose tissue of trout. This is in good agreement with the measurement of the CPT activity in the same tissues. The [IC(50)] that reflects the sensitivity to malonyl-CoA inhibition was 0.116+/-0.004 microM for the liver and 0.426+/-0.041 microM for the white muscle. These results demonstrate for the first time the existence of at least one gene encoding for CPT I present in both the liver and the muscle of rainbow trout.

Improvement in the efficiency of oxidative phosphorylation in the freshwater eel acclimated to 10.1 MPa hydrostatic pressure

Previous studies have suggested that the efficiency of oxidative phosphorylation in the freshwater eel (Anguilla anguilla) is increased after acclimation to high hydrostatic pressure. Analysis at atmospheric pressure of the respiratory chain complexes showed that, after 21 days at 10.1 MPa, the activity of complex II was decreased to approximately 50 % (P&lt;0.01) of the control value and that cytochrome c oxidase (complex IV) activity was significantly increased to 149 % of the control value (P&lt;0.05). ADP/O ratios calculated from mitochondrial respiration measurements were significantly increased after acclimation to high hydrostatic pressure (2.87 versus 2.52, P&lt;0.001) when measured in the presence of pyruvate plus malate at atmospheric pressure. These results clearly show an increased oxidative phosphorylation efficiency in response to high-pressure acclimation.

Lactate transport across sarcolemmal vesicles isolated from rainbow trout white muscle

Rainbow trout (Oncorhynchus mykiss) retain the majority of lactate produced during exhaustive exercise within white muscle. Previous studies have suggested that this retention is partially via a re-uptake of released lactate. The purpose of this work was to study lactate uptake using trout white muscle sarcolemmal vesicles. Lactate uptake by trout white muscle is partially through a low-affinity, high-capacity carrier (apparent K(m)=55.6 mmol l(−)(1) and V(max)=44.5 nmol mg(−)(1)protein min(−)(1)). At high concentrations (20 and 50 mmol l(−)(1)), pyruvate partially (up to 39 %) inhibited lactate uptake, suggesting the involvement of a monocarboxylate carrier. The anion transport inhibitor 4-acetoamido-4′-isothiocyanstilbene-2,2′-disulphonic acid (SITS) and the monocarboxylate transport inhibitor (α)-cyano-4-hydroxycinnamate (CHC) stimulated apparent lactate uptake. The model developed suggests that lactate is taken up by the vesicles, at least in part by a pyruvate-sensitive monocarboxylate carrier, and that its subsequent efflux is inhibited by SITS and CHC, suggesting that lactate export from trout white muscle is also carrier-mediated.

Short-term effects of 3,5,3'-triiodothyronine on the intermediary metabolism of the dogfish shark Squalus acanthias: evidence from enzyme activities

Plasma 3,5,3'-triiodothyronine (T3) concentration decreased significantly (P < 0.05), during 1-5 days of captivity, from levels in the freshly caught dogfish shark Squalus acanthias. The short-term effects of T3 treatment on the intermediary metabolism of S. acanthias were measured in the gill, kidney, liver, and white muscle. Animals were kept for 1-5 days before experimentation. Three hours after an intraperitoneal injection with either a low T3 dose (8.3 pmol T3/kg fish) or a high T3 dose (830 pmol T3/kg fish), selected enzymes of amino acid metabolism, lipid catabolism, ketone body metabolism, glycolysis, and oxidative metabolism were measured. Activity of enzymes of amino acid metabolism and lipid catabolism increased significantly (P < 0.05) in the liver of fish treated with a low T3 dose. The low dose of T3 apparently influences glycolysis as pyruvate kinase activity significantly increase (P < 0.05) in the kidney and white muscle.

An analysis of pH tolerance and substrate preference of isolated skeletal muscle mitochondria from Bufo marinus and Rana catesbeiana

1. The effects of varying pH and substrate on isolated skeletal muscle mitochondria from Bufo marinus and Rana catesbeiana were investigated. 2. For both species, VO2 max significantly decreased at all pH < 7.3 (P < 0.05), while maximum values were observed at a pH range of 7.3-7.6 with B. marinus maintaining a greater VO2 max than R. catesbeiana. 3. Respiratory control values (RCR) decreased significantly at all pH < 6.9 for both species (P < 0.05). 4. Isolated mitochondria from both species were maintained at pH = 7.2 and O2 consumption measured under five separate substrate conditions. 5. A rank preference was established based upon state 3 and RCR values. 6. Substrate preference was identical for both species and interspecific comparisons revealed differences in state 3 respiration and coupling.