Muscle remodeling in relation to blood supply: implications for seasonal changes in mitochondrial enzymes
Department of Biology, Queen's University, Kingston, Ontario, Canada, K7L 3N6
Author for correspondence (e-mail:
moyesc{at}biology.queensu.ca)
Accepted 30 November 2004
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Summary |
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Key words: anemia, skeletal muscle, oxidative phosphorylation, energy metabolism
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Introduction |
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One model that has been used to explore the mitochondrial response to
environmental stress is cold acclimation in fish. Depending upon the species
and fiber type, muscle mitochondrial enzyme activities can more than double
(e.g. Johnston and Maitland,
1980; Johnston,
1982
; Egginton and Sidell,
1989
; Battersby and Moyes,
1998
). Paradoxically, the increase in mitochondrial content
coincides with a decrease in absolute metabolic rate due to reduced
temperature. In salmonids, skeletal muscle mitochondrial enzyme specific
activity increases to the same extent in exercise training
(Farrell et al., 1991
) and
cold acclimation (Battersby and Moyes,
1998
). Cold acclimation is usually also accompanied by an increase
in capillarity (Egginton and Cordiner,
1997
), frequently in parallel with changes in mitochondrial
content (Johnston, 1982
). The
genetic basis of remodeling of striated muscle energetics with cold
acclimation, both cardiac and skeletal, remains largely unexplored.
Since cold acclimation also induces an increase in relative ventricular
mass (Graham and Farrell,
1990; Taylor et al.,
1996
) we considered the possibility that each aspect of
cold-induced muscle remodeling (cardiac hypertrophy, skeletal muscle
angiogenesis, mitochondrial proliferation) could be attributed to changes in
hemodynamics, such as the ability of erythrocytes to penetrate the peripheral
vasculature. As water temperatures cool in the Fall, erythrocyte properties
change in ways that could influence perfusion. First, cooling an erythrocyte,
or any cell, causes the cell membrane to become more rigid. This reduces
erythrocyte deformability and, as a consequence, makes it more difficult for
the cell to penetrate the peripheral vasculature
(Hughes et al., 1982
;
Kikuchi et al., 1982
). Second,
erythrocyte perfusion may also be influenced by cell age
(Linderkamp and Meiselman,
1982
). Many temperate fish experience a burst of erythropoiesis in
Spring and by the time Fall cooling begins, most of the erythrocytes are
approaching the end of their lifespan (see
Nikinmaa, 1990
). The cell
membranes of old erythrocytes are more rigid due to lipid damage and
aggregation of membrane-associated protein. Consequently, the onset of Fall
cooling may reduce the capacity of the erythrocytes to penetrate the muscle
vasculature. This could explain the stimulation of angiogenesis, a response
that is often linked to regional hypoxia
(Maxwell and Ratcliffe, 2002
).
While there is no evidence that mitochondrial gene expression is directly
sensitive to oxygen levels, erythrocytes have important antioxidant roles and
may be an important element of peripheral antioxidant defense by metabolizing
ROS (Gabbianelli et al., 1998
;
Aoshiba et al., 1999
;
Fedeli et al., 2001
). While
the antioxidant capacities of erythrocytes do not deteriorate with cell age
(e.g. Moyes et al., 2002
),
reduced penetration of the vascular beds could impair erythrocyte-dependent
antioxidant capacities. Thus, seasonal changes in erythrocyte properties could
contribute to the remodeling of both the vasculature and energetics in
skeletal muscle.
In the present study we examined the impact of erythrocyte dynamics on muscle mitochondrial biogenesis. First, we induced an anemic state to reduce the number of erythrocytes. We assume that this would create a situation where fewer erythrocytes passed through the muscle vasculature. Second, we assessed if the age profile of erythrocytes could influence the effects of seasonal cooling on mitochondrial enzyme changes. Animals made anemic were able to replenish their erythrocyte compliment over several weeks at constant temperature. By the time Fall cooling began, their hematocrit had returned to normal levels, but the cells were largely young cells. Collectively, these studies assessed the impact of perfusion on muscle mitochondrial biogenesis.
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Materials and methods |
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At the onset of experiments, fish averaged about 75 g(±6 g
S.E.M.). Fish were made anemic by injection of phenylhydrazine
(protocol approved by Queen's University Animal Care Committee), as described
by Gilmour and Perry (1996).
They were anesthetized in bicarbonate-buffered MS222 (0.4 g NaHCO3
and 0.2 g MS-222 per litre water) and injected with phenylhydrazine (10 µg
g-1). Control fish were anesthetized but not injected. Injections
occurred when water temperature was 18°C. The phenylhydrazine treatment
had no effect on mortality; over the 25 week period, no fish died in either
treated or control group. There was also no significant effect on growth rates
in treated and untreated fish at either 1 month (95±7 g vs
88±6 g) or 6 months (122±6 g vs 115±8 g)
post-treatment.
At the onset of the study, 10 untreated fish were sampled as a pre-treatment group (designated Week 0). Groups of five treated fish were sampled at 1, 2, 4, 8 days post-treatment, and compared with pre-treatment fish. For subsequent time points (weeks to 6 months) five fish were sampled from both control and phenylhydrazine-treated groups. Fish were anesthetized in MS222, blood samples were collected, then fish were decapitated and tissues sampled. Cardiac ventricle mass was measured in relation to body weight, giving relative ventricular mass. Tissues (red muscle, white muscle, heart) were flash frozen, powdered in liquid nitrogen, and stored at 80°C.
Enzyme analyses
Powdered tissue (50100 mg) was weighed and homogenized in 20 volumes
of extraction buffer consisting of 20 mmol l-1 Hepes (pH 7.0), 1
mmol l-1 EDTA, and 0.1% Triton X-100, using a ground glass tissue
homogenizer. Enzyme activities were assayed using a Molecular Devices
Spectramax 250 spectrophotometer at 25°C at 340 nm unless otherwise noted.
After the assays for COX, CPT and HOAD, the homogenates were frozen at
80°C prior to analyses of other enzymes. Chemicals were purchased
from Sigma-Aldrich Canada, Oakville, Canada.
Cytochrome oxidase (COX)
The COX assay was performed within 60 min following homogenization. In
brief, homogenate was added to a mixture of Tris-HCl (50 mmol l-1)
containing 50 µmol l-1 reduced cytochrome c. After rapid mixing,
the absorbance (550 nm) was followed for up to 90 s. Homogenate volumes were
chosen to ensure that the rate of change in absorbance fell within the range
of 0.06 to 0.10 absorbance units per minute. Above this rate, the reaction
depleted cytochrome c concentrations enough to reduce reaction rates.
Citrate synthase (CS)
The assay contained (in mmol l-1):
5,5'-dithiobis-(2-nitrobenzoic acid) (0.1), acetyl CoA (0.3),
oxaloacetate (0.5), in Tris-HCl (50), pH 8.0. The increase in absorbance at
412 nm was measured. A control well lacking oxaloacetate was used to correct
for background thiolase activity.
ß-hydroxyacyl CoA dehydrogenase (HOAD)
The assay contained (in mmol l-1): acetoacetylCoA (0.1), NADH
(0.15) in imidazole (50) at pH 7.2. The assay was started with enzyme and no
NADH oxidation was evident in the absence of acetoacetylCoA.
Pyruvate kinase (PK)
The assay contained (in mmol l-1): ADP (5), KCl (100),
MgCl2 (10), NADH (0.15), fructose 1,6 bis-phosphate (0.01),
phosphoenolpyruvate (5) and excess lactate dehydrogenase (free of PK) in 50
mmol l-1 Mops 7.4. The assay was started with enzyme but was
strictly dependent upon phosphoenolpyruvate.
Lactate dehydrogenase (LDH)
The assay contained (in mmol l-1): pyruvate (1), NADH (0.15) in
Hepes (50) at pH 7.0.
Carnitine palmitoyl transferase (CPT)
The assay contained (in mmol l-1):
5,5'-dithiobis-(2-nitrobenzoic acid (0.1), palmitoyl CoA (0.1) and
carnitine (5) in Tris-HCl (50) at pH 8.0. Control wells lacking carnitine were
used to correct for background thiolase. Absorbance was monitored at 412 nm.
Since freezing inactivates CPT I, it is presumed that the activity measured in
the CPT assay is CPT II.
DNA analyses
Homogenates were also used to measure the levels of DNA. A small volume of
homogenate (50 µl) was added to 5 volumes of proteinase K digestion buffer
(10 mmol l-1 Tris, 100 mmol l-1 NaCl, 25 mmol
l-1 EDTA, 0.5% SDS, 0.2 mg ml-1 proteinase K) in the
presence of RNase (Battersby and Moyes
1998). After 16 h at 55°C, and without further purification,
the DNA concentration was measured using Picogreen (Molecular Probes) and a
standard curve constructed using purified trout genomic DNA.
Although tissues were blotted prior to freezing, we did not perfuse the
tissues to expel erythrocytes. However, erythrocyte DNA levels in whole blood
(0.3 mg g-1 blood; Moyes
et al., 2002
) are much lower than heart DNA levels (3 mg
g-1 tissue; Leary et al.,
1998
). Similarly, the levels of mtDNA do not appreciably influence
total DNA levels in these tissues. In skeletal muscles, mtDNA is less than 1%
of total DNA (Battersby and Moyes,
1998
). Thus, neither blood contamination nor mtDNA would
substantially affect the DNA determinations.
Statistical analyses
Time courses were analyzed by analysis of variance (ANOVA) followed by a
Tukey's test post-hoc. Differences with P<0.05 were considered
significant. The analyses compared treated animals to time-matched controls at
all sampling points of two weeks post-treatment or longer. However, the
samples collected in the short time course (1, 2, 4, 8 days) were compared
with a group untreated animals collected at the start of the experiment as
designated as week 0, or pre-treatment.
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Results |
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Relative ventricular mass changed rapidly in response to anemia (Fig. 1B). By 2 weeks post-injection, ventricular mass had increased from 0.085% to 0.11% of body mass (P=0.001). Relative ventricular mass had decreased by 9 weeks post-injection. By the time Winter cooling had occurred, the control fish had experienced enough cardiac growth to match the phenylhydrazine treated fish. At the lowest winter temperatures, phenylhydrazine treated fish and control fish had similar relative ventricular masses of about 0.1% of body mass. Thus, anemic history had no effect on the relative ventricular mass in acclimated fish.
DNA levels were also measured in ventricle to assess the impact of (1) anemia, (2) seasonal acclimation and (3) an anemic history on ventricular remodeling. Although we consider the primary effect of phenylhydrazine to be anemia, other effects are possible (see Discussion). Anemia alone had no effect on the DNA concentration per gram ventricle (Fig. 2B) but the DNA content in the entire ventricle increased 28% (Fig. 2C). Conversely, cold acclimation alone caused a 30% decline in DNA concentration per gram ventricle (Fig. 2B, dark bars), but DNA content per ventricle did not change (Fig. 2C, dark bars). Finally, there was no evidence that an anemic history influenced the effects of cold acclimation. By 25 weeks acclimation, the treated and untreated fish had similar relative ventricular masses (Fig. 2A), DNA concentrations per gram ventricle (Fig. 2B) and DNA contents per ventricle (Fig. 2C).
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Ventricular enzyme activities were also assessed in these fish (Fig. 3). In heart, the effects of phenylhydrazine treatment on enzymes must be interpreted with consideration of the effects on relative ventricular mass (Fig. 2). There was no significant effect of anemia on HOAD specific activity (P=0.08). Similarly, the specific activities of COX, CS and CPT did not change with anemia. The relative maintenance of specific activity required active synthesis of enzymes to compensate for the increase in relative ventricular mass.
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Muscle enzymes
We investigated the effects of phenylhydrazine treatment on enzymes in
white muscle, red muscle and cardiac ventricle. Figs
4 and
5 show the effects of
phenylhydrazine treatment on enzymes over 4 weeks, which we interpret to be
the impact of anemia. Fig. 6
shows the enzyme patterns that occurred in treated and untreated fish as a
function of thermal acclimation. Upon acclimation, the phenylhydrazine-treated
fish had lived with a normal hematocrit for several months. Thus, the
difference between control and phenylhydrazine-treated fish arises from the
`anemic history', which we presume to be due to the influence of red blood
cell age.
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In white muscle (Fig. 4) CS and COX activities were largely unaffected by phenylhydrazine treatment. We also measured the activities of the glycolytic enzymes LDH and PK in white muscle to assess the response of glycolytic genes to the treatment. Neither LDH nor PK showed a significant response to phenylhydrazine treatment.
The effects of phenylhydrazine treatment on red muscle enzymes were less clear (Fig. 5). Individual enzymes appeared to increase or decrease within a range of about 15% in the first week of anemia. None showed systematic changes in activity with anemia.
The anemic history (i.e. a younger erythrocyte population) had little effect on enzymes in skeletal muscle upon cold acclimation (Fig. 6). It did not blunt the increases in COX and CS in red or white muscle. However, an anemic history did appear to enhance the effects on PK and LDH. Specifically, the anemic history caused a reduction in PK levels upon cold acclimation, whereas cold acclimation alone had no significant effect. Cold acclimation alone depressed LDH activity, but the anemic history further depressed LDH specific activity.
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Discussion |
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Effects of anemia on skeletal muscles
Many factors influence the ability of erythrocytes to penetrate the
peripheral vasculature. Erythrocyte content of the blood can influence oxygen
delivery to the periphery by changing O2 content of the blood.
Direct manipulation of erythrocyte O2 content can compromise
max,
decreasing it at low hematocrit and enhancing it at high hematocrit in fish
(Gallaugher et al., 1995
) and
mammals (Davies et al., 1982
).
Viscoelastic properties of the erythrocyte also influence penetration into the
capillaries. Membrane elasticity, as well as cytoskeletal rigidity, influences
the deformability of the erythrocyte. When erythrocytes are cold, the reduced
fluidity of the lipid bilayer reduces membrane elasticity, altering
deformability and the ability to penetrate capillary beds
(Hughes et al., 1982
;
Kikuchi et al., 1982
).
Cellular aging also increases membrane rigidity, reducing deformability
(Linderkamp and Meiselman,
1982
). Since Winter-acclimatized fish would experience both of
these changes (aging and temperature), we examined if alterations in
erythrocyte properties could induce the change in muscle mitochondrial
content. Neither of our approaches to altering peripheral oxygen delivery
caused changes in the activity of mitochondrial enzymes.
Anemia, induced by phenylhydrazine, failed to alter the levels of any
mitochondrial enzyme in either white muscle
(Fig. 4) or red muscle
(Fig. 5). Pre-acclimation
anemia, with the resultant rejuvenation of erythrocyte population, addressed
the impact of erythrocyte age on seasonal changes in muscle energetics.
Experimental temperatures cooled long after the fish had recovered from the
anemia. Cytochrome oxidase increased about 50% in white muscle and about 30%
in red muscle (Fig. 6), in line
with previous studies on cold acclimation
(Battersby and Moyes, 1998).
The treated fish, with anemic history, exhibited the same pattern of
cold-induced changes in mitochondrial enzymes.
Cold acclimation in trout can cause an increased reliance on lipids for
muscle during exercise (Kieffer et al.,
1998). In this study, analysis of red muscle revealed no
significant changes in the activities of fatty acid oxidizing enzymes (CPT and
HOAD) as a result of cold acclimation or anemic history.
Cardiac remodeling in anemia and cold acclimation
Both anemia and cold-acclimation induced ventricular remodeling, with
important differences. Norman and McBroom
(1958) found that
phenylhydrazine treatment induced cardiac growth in rats. The myocardial
changes associated with phenylhydrazine treatment likely arise from anemia and
the resultant cardiovascular effects, however, it is important to recognize
other potential effects of phenylhydrazine treatment. Meerson and Evsevieva
(1985
) found that the effects
of phenylhydrazine on cardiac growth could be largely prevented by
co-treatment with an antioxidant, suggesting that the phenylhydrazine might be
acting through direct effects on the heart. Nonetheless, it is clear that the
cardiac remodeling with phenylhydrazine treatment differed from that seen with
cold acclimation, despite similar effects on relative ventricular mass.
Previous studies in salmonids and other species have shown that relative
ventricular mass increases by about 30% in cold acclimated fish
(Graham and Farrell, 1990;
Taylor et al., 1996
;
Farrell et al., 1988
). Our
sampling protocol also allowed us to follow the time course of change.
Relative ventricular mass remained constant as temperature dropped from
20°C to 10°C. However, within 2 weeks of temperatures reaching the
seasonal low (1.8°C), relative ventricular mass had increased about 30%. A
similar degree of ventricular growth was seen in response to anemia
(Fig. 2). Cold temperature is
likely to be accompanied by increased peripheral resistance
(Taylor et al., 1996
;
Farrell et al., 1988
),
possibly due to elevated plasma viscosity and reduced erythrocyte
deformability (see Egginton,
2002
). In contrast, ventricular remodeling in anemic fish probably
occurred as a response to a chronic increase in cardiac output to maintain
oxygen delivery to the periphery.
Although the increase in relative ventricular mass with anemia was similar
to the change with cold acclimation, cellular changes in DNA content imply
different mechanisms of ventricular growth. While the exact nature of
cold-induced changes in relative ventricular mass is unclear, the analyses of
DNA content are consistent with hypertrophy; relative ventricular mass
increased but the total DNA content of the ventricle was unchanged. The most
parsimonious explanation is that increases in relative ventricular mass arise
from increases in cardiomyocyte size. In contrast to the situation with
cold-acclimation, the increase in relative ventricular mass that accompanied
anemia was accompanied by an increase in DNA content. While these observations
are consistent with cardiomyocyte hyperplasia, it is important to acknowledge
the other potential explanations for increase DNA content per ventricle.
Cardiomyocytes comprise the bulk of ventricular mass, but they are not the
most abundant type of cell within the heart. Fibroblasts, immune cells,
vascular smooth muscle, endothelial cells and other cell types collectively
account for more than 70% of the cells in a vertebrate heart (e.g. Alder et
al., 1996). Thus, proliferation of non-cardiomyocytes could account for the
increased DNA content of ventricle. Another potential explanation is
cardiomyocyte polyploidy. While most cardiomyocytes are generally thought to
be terminally differentiatied, mononucleated cells
(Zak, 1974), under some
conditions the cardiomyocytes can re-enter karyokinesis and become polyploid
(Kellerman et al., 1992
).
While we cannot discount these potential explanations for the increase in both
ventricular DNA content and ventricular growth, recent studies have
established that cardiomyocyte hyperplasia contributes to ventricular growth
under disease conditions. These cardiomyocyte precursor cells may be
pre-cardiomyocytes that proliferate and differentiate, or a pool of
circulating stem cells that invade cardiac tissue
(Anversa and Kajstura, 1998
;
Nadal-Ginard et al., 2003
).
Based on estimates of trout cardiomyocyte volume, Clark and Rodnick
(1998
) concluded that
hyperplasia was also necessary to account for the increase in relative
ventricle mass seen during fish growth.
The patterns seen in ventricle enzymes, in relation to mass and DNA can be interpreted in terms of both causes and consequences. The cause of the change in total enzyme content of the ventricle (specific activity x mass) reflects a genetic event that culminates in a change in synthesis or degradation of enzymes. Thus, the 4050% increase in total activity of COX and CS upon cold acclimation (Fig. 3) reflects a stimulation of mitochondrial proliferation.
The increase in mitochondrial enzyme content that accompanies the increase
in ventricular mass served to maintain nearly constant the enzyme specific
activity. Across each treatment (i.e. anemia, anemic history, temperature
acclimation) the specific activities of each enzyme varied less than 15%. The
specific activity of CPT, an index of the propensity for fatty acid oxidation,
was relatively unaffected by anemia (treated vs untreated at 4
weeks), cold acclimation (untreated at 4 vs 25 weeks), or anemic
history (treated vs untreated at 25 weeks). The same was true for
HOAD, another index of fatty acid oxidation
(Fig. 3). Changes in indices of
fatty acid oxidation often accompany cardiac hypertrophy. For example, HOAD
specific activities increase in the cardiac hypertrophy that accompanies
sexual maturation of trout (Clark and
Rodnick, 1998). In mammalian models, hypertensive hypertrophy is
accompanied by a change in fuel preference away from fatty acids and toward
carbohydrates (Barger and Kelly,
1999
).
In summary, we found little evidence that our treatments, which targeted erythrocyte properties (hematocrit, age profile), affected the mitochondrial enzyme profile in skeletal muscle. Our manipulation of erythrocyte age profile did not alter the seasonal response of skeletal muscle enzymes. We cannot rule of the effects of temperature-dependent effects on erythrocyte deformability, but even severe anemia failed to alter mitochondrial biogenesis. While the effects of anemia on COX activity were significant, the rapidity of the response suggests a post-translational route of enzyme activation, rather than induced expression. It is possible that elevating activity levels of the fish could exacerbate oxygen delivery limitations, and enhance the seasonal compensatory response.
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Acknowledgments |
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Footnotes |
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References |
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---|
Adler, C. P., Friedburg, H., Herget, G. W., Neuburger, M. and Schwalb, H. (1996). Variability of cardiomyocyte DNA content, ploidy level and nuclear number in mammalian hearts. Virchows Arch. 429,159 -164.[Medline]
Anversa, P. and Kajstura, J. (1998).
Ventricular myocytes are not terminally differentiated in the adult mammalian
heart. Circ. Res. 83,1
-14.
Aoshiba, K., Nakajima, Y., Yasui, S., Tamaoki, J. and Nagai,
A. (1999). Red blood cells inhibit apoptosis of human
neutrophils. Blood 93,4006
-4010.
Barger, P. M. and Kelly, D. P. (1999). Fatty acid utilization in the hypertrophied and failing heart: Molecular regulatory mechanisms. Am. J. Med. Sci. 318, 36-42.[CrossRef][Medline]
Battersby, B. J. and Moyes, C. D. (1998). Influence of acclimation temperature on mitochondrial DNA, RNA, and enzymes in skeletal muscle. Am. J. Physiol. 275,R905 -R912.[Medline]
Clark, R. J. and Rodnick, K. J. (1998).
Morphometric and biochemical characteristics of ventricular hypertrophy in
male rainbow trout (Onchorhynchus mykiss). J. Exp.
Biol. 201,1541
-1552.
Davies, K. J., Maguire, J. J., Brooks, G. A., Dallman, P. R. and Packer, L. (1982). Muscle mitochondria bioenergetics, oxygen supply, and work capacity during dietary iron deficiency and repletion. Am. J. Physiol. 242,E418 -E427.[Medline]
Egginton, S. (2002). Temperature and angiogenesis: the possible role of mechanical factors in capillary growth. Comp Biochem Physiol A mol Integr Physiol. 132,773 -787.[CrossRef][Medline]
Egginton, S. and Sidell, B. D. (1989). Thermal acclimation induces adaptive changes in subcellular structure of fish skeletal muscle. Am. J. Physiol. 256, R1-R9.[Medline]
Egginton, S. and Cordiner, S. (1997).
Cold-induced angiogenesis in seasonally acclimatized rainbow trout
(Oncorhynchus mykiss). J. Exp. Biol.
200,2263
-2268.
Farrell, A. P., Johansen, J. A. and Suarez, R. K. (1991). Effects of exercise-training on cardiac performance and muscle enzymes in rainbow trout, Oncorhynchus mykiss. Fish Physiol. Biochem. 9,303 -312.
Farrell, A. P., Hammons, A. M., Graham, M. S. and Tibbits, G. (1988). Cardiac growth in rainbow trout, Salmo gairdneri. Can. J. Zool. 66,2368 -2373.
Fedeli, D., Tiano, L., Gabbianelli, R., Caulini, G. C., Wozniak, M. and Falcioni, G. (2001). Hemoglobin components from trout (Salmo irideus): determination of their peroxidative activity. Comp. Biochem. Physiol. B Biochem. Mol. Biol. 130,559 -564.[CrossRef][Medline]
Gabbianelli, R., Santroni, A. M., Fedeli, D., Kantar, A. and Falcioni, G. (1998). Antioxidant activities of different hemoglobin derivatives. Biochem. Biophys. Res. Comm. 242,560 -564.[CrossRef][Medline]
Gallaugher, P., Thorarensen, H. and Farrell, A. P. (1995). Hematocrit in oxygen transport and swimming in rainbow trout (Oncorhynchus mykiss). Respir. Physiol. 102,279 -292.[CrossRef][Medline]
Gilmour, K. M. and Perry, S. F. (1996). The effects of experimental anemia on CO2 excretion in vitro in rainbow trout, Oncorhynchus mykiss. Fish Physiol. Biochem. 15, 83-94.
Graham, M. S. and Farrell, A. P. (1990). Myocardial oxygen consumption in trout acclimated to 5°C and 15°C. Physiol. Zool. 63,536 -554.
Hood, D. A. (2001). Contractile
activity-induced mitochondrial biogenesis in skeletal muscle. J.
Appl. Physiol. 90,1137
-1157.
Hughes, G. M., Kikuchi, Y. and Watari. H. (1982). A study of the deformability of red blood cells of a teleost fish, the yellowtail (Seriola quinqueradiata), and a comparison with human erythrocytes. J. Exp. Biol. 96,209 -220.[Abstract]
Jackson, M. J. et al. (2002). Antioxidants, reactive oxygen and nitrogen species, gene induction and mitochondrial function. Mol. Aspects Med. 23,209 -285.[CrossRef][Medline]
Johnston, I. A. (1982). Capillarisation, oxygen diffusion distances and mitochondrial content of carp muscles following acclimation to summer and winter temperatures. Cell Tissue Res. 222,325 -337.[Medline]
Johnston, I. A. and Maitland, B. (1980). Temperature acclimation in crucian carp Carassius carrassius L., morphometric analyses of muscle fibre ultrastructure. J. Fish Biol. 17,113 -125.
Johnston, I. A., Manthri, S., Smart, A., Campbell, P., Nickell,
D. and Alderson, R. (2003). Plasticity of muscle fibre number
in seawater stages of Atlantic salmon in response to photoperiod manipulation.
J. Exp. Biol. 206,3425
-3435.
Kellerman, S., Moore, J. A., Zierhut, W., Zimmer, H. G., Campbell, J. and Gerdes, A. M. (1992). Nuclear DNA content and nucleation patterns in rat cardiac myocytes from different models of cardiac hypertrophy. J. Mol. Cell. Cardiol. 24,497 -505.[CrossRef][Medline]
Kieffer, J. D., Alsop, D. and Wood, C. M.
(1998). A respirometric analysis of fuel use during aerobic
swimming at different temperatures in rainbow trout (Oncorhynchus
mykiss). J. Exp. Biol.
201,3123
-3133.
Kikuchi, Y., Hughes, G. M. and Albers, C. (1982). Temperature dependence of the deformability of carp (Cyprinus carpio) red blood cells. Experientia. 38,822 -824.[Medline]
Korshunov, S. S., Skulachev, V. P. and Starkov, A. A. (1997). High protonic potential actuates a mechanism of production of reactive oxygen species in mitochondria. FEBS Lett. 416,15 -18.[CrossRef][Medline]
Leary, S. C., Battersby, B. J. and Moyes, C. D.
(1998). Inter-tissue differences in mitochondrial enzyme
activity, RNA and DNA in rainbow trout (Oncorhynchus mykiss).
J. Exp. Biol. 201,3377
-3384.
Leary, S. C. and Moyes, C. D. (2000). The effects of bioenergetic stress and redox balance on the expression of genes critical to mitochondrial function. In Cell and Molecular Responses to Stress, vol. 1, Environmental Stressors and Gene Repressors (ed. K. B. Storey and J. Storey), pp.209 -229. Amsterdam, The Netherlands: Elsevier Press.
Linderkamp, O. and Meiselman, H. J. (1982). Geometric, osmotic, and membrane mechanical properties of density-separated human red cells. Blood 59,1121 -1127.[Abstract]
Maxwell, P. H. and Ratcliffe, P. J. (2002). Oxygen sensors and angiogenesis. Semin. Cell Dev. Biol. 13,29 -37.[CrossRef][Medline]
Meerson, F. Z. and Evsevieva, M. E. (1985). Disturbances of the heart structure and function in chronic hemolytic anemia, their compensation with increased coronary flow, and their prevention with ionol, an inhibitor of lipid peroxidation. Adv. Myocardiol. 5,201 -211.[Medline]
Moyes, C. D., Sharma, M. L., Lyons, C. N., Leary, S. C., Leon, M., Petri, A., Lund, S. and Tufts, B. L. (2002). Origins and consequences of mitochondrial decline in nucleated erythrocytes. Biochim. Biophys. Acta. 1591,11 -20.[CrossRef][Medline]
Moyes, C. D. and Hood, D. A. (2003). Origins and consequences of mitochondrial variation in vertebrate muscle. Annu. Rev. Physiol. 65,177 -201.[CrossRef][Medline]
Nadal-Ginard, B., Kajstura, J., Leri, A. and Anversa, P.
(2003). Myocyte death, growth, and regeneration in cardiac
hypertrophy and failure. Circ. Res.
92,139
-150.
Nikinmaa, M. (1990). Vertebrate Red Blood Cells. Berlin, Heidelberg, Germany: Springer-Verlag.
Norman, T. D. and McBroom, R. D. (1958). Cardiac hypertrophy in rats with phenylhydrazine anemia. Circ. Res. 6,765 -770.[Medline]
Pearlstein, D. P., Ali, M. H., Mungai, P. T., Hynes, K. L.,
Gewertz, B. L. and Schumacker, P. T. (2002). Role of
mitochondrial oxidant generation in endothelial cell responses to hypoxia.
Arterioscler. Thromb. Vasc. Biol.
22,566
-573.
Scarpulla, R. C. (2002). Nuclear activators and coactivators in mammalian mitochondrial biogenesis. Biochim. Biophys. Acta 1576,1 -14.[Medline]
Taylor, S. E., Egginton, S. and Taylor E. W.
(1996). Seasonal temperature acclimatization of rainbow trout:
cardiovascular and morphometric influences on maximal sustainable exercise
level. J. Exp. Biol.
199,835
-845.
Turner, C. and Schapira, A. H. (2001). Mitochondrial dysfunction in neurodegenerative disorders and ageing. Adv. Exp. Med. Biol. 487,229 -251.[Medline]
Zak, R. (1974). Development and proliferative capacity of cardiac muscle cells. Circ. Res. 35 (Suppl. 2),17 -26.[Medline]