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University of Western Ontario, London N6A 5B7; Wilfrid Laurier University, Waterloo N2L 3C5; and University of Waterloo, Waterloo N2L 3G1, Ontario, Canada
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
ACKNOWLEDGEMENTS
FOOTNOTES
REFERENCES
ABSTRACT 
Kelly, D. A., P. M. Tiidus, M. E. Houston, and E. G. Noble.
Effect of vitamin E deprivation and exercise training on induction
of HSP70. J. Appl. Physiol. 81(6):
2379-2385, 1996.
To investigate the effects of dietary vitamin E
deprivation and chronic exercise on the relative content of selected
isoforms of the heat-shock protein 70 (HSP70) family in rat hindlimb
muscle, vitamin E was withheld for 16 wk from female rats that
underwent treadmill run training during the final 8 wk. As indicated by
increased (P < 0.05) content of the
stress-inducible isoform (HSP72), training did stress the exercising
muscles. However, vitamin E deficiency did not alter HSP72 content in
nontrained rats and was associated with a lesser induction
(P < 0.01) in some muscles of
trained animals. The constitutive isoform, which exhibited similar
levels in muscles of varying fiber types, was demonstrated to be
largely refractory to exercise, with an equivocal response to vitamin E
deprivation. HSP72 content was correlated to type I myosin heavy chain
(MHC-I) content but only in muscles of sedentary normal-diet rats.
After training, HSP72 content in a muscle essentially devoid of MHC-I
(superficial vastus lateralis) reached levels comparable to those in a
muscle high in MHC-I (soleus).
antioxidant; heat-shock proteins; oxidative stress; rat; skeletal
muscle; type I myosin
INTRODUCTION A SINGLE BOUT of exhaustive exercise has previously
been demonstrated to enhance or induce the synthesis of the 70-kDa
family of heat-shock proteins (HSP72; Refs. 15, 17, 25), a
highly conserved group of proteins known to perform key roles in
cellular protein transport and stability (20). As in other systems
(20), exercise-induced increases in HSP72 in mammalian muscle appear to
follow increases in heat-shock transcription factor (17) and subsequent
elevation of HSP72 mRNA (17, 25). The exact factor(s) associated with
exercise that initiates this sequence of events, however, remains to be
determined.
Vitamin E is the principal intramembrane antioxidant and membrane
stabilizer. Vitamin E depletion has been demonstrated to disrupt
organelle membrane function (31). If the degree of membrane disruption
were sufficient to result in cell damage, particularly in combination
with exercise (1), initiation of the heat-shock response might occur
(20). Also, it has been suggested that oxidative stress may be a direct
initiator of the heat-shock response (25). Vitamin E both directly
quenches such oxyradicals as singlet oxygen and superoxide
and also interrupts the chain reaction of phospholipid peroxidation
initiated by reactive radicals (10). Oxyradical formation appears to be
an inevitable consequence of mitochondrial metabolism. Aerobic exercise
may increase production of such species due to increased oxygen flux
through oxidative energetic systems (11) and as a result of
mitochondrial uncoupling associated with elevated temperatures during
exercise (25). In both instances, intracellular oxidative stress would
be increased and could account for initiation of HSP synthesis (25).
Thus vitamin E depletion may affect HSP72 production via various
mechanisms.
Because exercise and vitamin E status may both impact on HSP72 content,
dietary vitamin E depletion and endurance exercise training alone and
in combination were used in the present study. Trained animals were
used because it was conjectured that compared with naive animals they
would have accommodated to many of the stresses associated with a
single bout of exercise. Posttraining accommodations would
include greater familiarity with the exercise protocol, reduced
temperature elevations, and lesser disruption of cellular homeostasis
(3). Hence, these studies sought to determine whether the increases in
HSP72 known to occur after acute exhaustive exercise (15, 25) are
maintained throughout chronic exercise training. It was further
hypothesized that vitamin E depletion would selectively enhance the
oxidative stress experienced by the exercising muscle. This paradigm
could hence be employed to investigate the possible involvement of
oxidative insult in the HSP72 response previously noted with a single
bout of exercise.
MATERIALS AND METHODS Animals. This study was approved by
the University of Waterloo Committee on Animal Care and performed in
accordance to the guiding principles of the Canadian Council on Animal
Care. This experiment employed muscle tissue derived from female Wistar
rats obtained from Charles River Laboratories. Previous reports have detailed other aspects of the response of these animals to exercise training and vitamin E deficiency (27-29). At ~6 wk of age,
animals were assigned randomly to either the vitamin E-deprived
( Training procedures. After 8 wk of
diet, animals chosen randomly from both +E and Tissue collection
procedures. Animals in exercise-trained +E
(+ET) and Sodium dodecyl sulfate (SDS)-polyacrylamide gel
electrophoresis. Frozen samples of ~100-mg mass were
homogenized in 1 ml of 600 mM NaCl, 15 mM tris(hydroxymethyl)
aminomethane (Tris) · HCl (pH 7.5). Equal amounts of
protein from homogenized samples were separated by mass via
one-dimensional (1-D) SDS polyacrylamide gel electrophoresis by using a
1.5-mm-thick 10% polyacrylamide gel (15). Amersham Rainbow Protein
molecular weight markers (RPN.756) were co-electrophoresed to help
identify both the inducible (HSP72) and constitutive (HSC73) isoforms
of the 70-kDa family of HSPs. Additionally, as a positive control,
samples were run against standards containing a high constitutive
concentration of HSP70s and MHC-I (Sprague-Dawley rat Sol muscle
homogenates).
Protein transfer and immunoblotting.
After electrophoretic separation, proteins were transferred to
nitrocellulose membranes (0.2 µm thick; Bio-Rad) by using Bio-Rad
mini-protean II gel system at 15 V for 12 h in 20% methanol-1.44%
glycine buffer (pH 8.3) containing 0.1% SDS and 0.3%
Tris · HCl. Gels were then stained for 4 h with 0.5%
Coomassie brilliant blue G in 20% methanol-10% glacial acetic acid
solution and destained overnight with 20% methanol-10% glacial acetic
acid solution to check for completeness of transfer. Nitrocellulose
membranes containing protein were blocked for a minimum of 5 h by using
5% skim milk powder in Tris-buffered saline (TBS; 500 mM NaCl, 20 mM
Tris · HCl pH 7.5), washed twice (5 min each) in TBS
containing 0.5% Tween 20 (TTBS), and reacted with primary antibody
(StressGen SPA-810 monoclonal anti-HSP72 diluted 1:750; StressGen
SPA-815 monoclonal anti-HSC73 diluted 1:750; or 10D10 monoclonal
anti-MHC-I, a gift from P. Merrifield, diluted 1:750) in TTBS
containing 2% skim milk powder for 16 h. After two washes of 5 min
each in TTBS, membranes were reacted with goat-anti-mouse
immunoglobulin G-conjugated alkaline phosphatase (Bio-Rad; 1:1,000
dilution in TTBS containing 2% skim milk powder), washed twice again
in TTBS, and washed once in TBS (5 min each). Blots were then developed
in bicarbonate buffer (100 mM
NaCO3, 1 mM
MgCl2, pH 9.8) containing 0.03%
p-nitro blue tetrazolium chloride
p-toluidine salt, dissolved in 70%
N, N-dimethylformamide and 0.015% 5-bromo-4-chloro-3-indolyl phosphate, dissolved in 100%
N, N-dimethylformamide.
Development was halted by immersion of membranes in distilled water.
Quantification of protein concentration was made by using a model 2202 LKB laser ultrascan densitometer equipped with an LKB 2220 recording integrator. Sample band concentrations were tabulated as a
percentage of the concentration recorded for a Sprague-Dawley rat Sol
sample (equal in protein content to the test sample) run on the same
blot.
Statistical analysis. Levels of HSP72,
HSC73, and MHC-I concentrations were reported as means ± SE and
compared by using a two-way analysis of variance test. On determination
of significant main effects or interaction, pairwise comparisons
employing a Student-Newman-Keuls post hoc test were conducted.
Differences were considered significant at
P < 0.05.
RESULTS It has been reported previously that tissue vitamin E concentrations
were reduced by over 90% in the animals on the Table 1.
Effects of 16 wk of vitamin E-free or normal diets and 8 wk of training
on muscle vitamin E concentration and succinate dehydrogenase activities
E) or normal diet (+E) group. The +E group was fed ad libitum
with AIN-76 semipurified rodent diet that included vitamin
E (50 IU/kg). The E group was fed a vitamin E-free AIN-76 diet.
E groups were
trained on a motorized treadmill by using a protocol detailed in the
study of Tiidus and Houston (28). After a 2-wk adaptation period during
which the speed and duration of treadmill running were continuously
increased, rats were trained for 6 wk, 5 days/wk, at a treadmill speed
of 40 m/min, 15% grade, for up to 60 min/day or until exhaustion, whichever came first. All rats continued to be fed on the
above-specified diets for the duration of the 8-wk training period.
Control +E and E diet animals did not participate in the
training procedures.
E (ET) groups
(n = 8 each) were killed 48 h after completion of the training program along with untrained +E
(n = 8) and E
(n = 8) control animals. Although some
tissue differences exist, studies employing heat stress demonstrated
increases in HSP72 content in skeletal muscle (7) and heart (12) that persisted for at least 2 days poststress. Animals were anesthetized with a 4% halothane/medical air mixture. Soleus (Sol), plantaris (Plant), and red (deep) (RV) and white (superficial) (WV) portions of
vastus muscles [muscles exhibiting a wide range of type I myosin heavy chain (MHC-I) content; Ref. 16] were rapidly removed, immediately frozen in liquid nitrogen, and stored at 80°C
for subsequent analysis. For the muscle samples employed in this study, vitamin E content, markers of lipid peroxidation [thiobarbituric acid reactive substances (TBARS) and malondialdehyde], and
succinate dehydrogenase (SDH) levels have been reported previously and
were determined as outlined (27, 28).
E diet (Table
1). Determination of muscle TBARS suggested
that vitamin E deprivation increased accumulation of lipid peroxides in
all muscles examined, whereas training elevated TBARS in Sol (+E and E groups) and Plant (+E group) muscles only.
Vitamin E, µmol
-tocopherol/g wet wt TBARS, nmol/g wet wt
Succinate Dehydrogenase, µmol · g wet
wt
1 · min1
Control
Trained
Control
Trained
Control
Trained
Soleus
+E
47.6 ± 12.3
31.1 ± 9.9*
100 ± 6
294 ± 10*
14.3 ± 3.1
19.9 ± 2.8*
E 0.2 ± 0.6
0.0 ± 0.0
294 ± 16
431 ± 35*
15.8 ± 2.7
20.7 ± 1.6*
Plantaris
+E
40.4 ± 6.0
29.7 ± 5.3*
117 ± 13
202 ± 10*
11.3 ± 1.9
16.2 ± 3.8*
E 0.9 ± 1.6
0.5 ± 0.7
225 ± 15
285 ± 25
9.9 ± 2.1
14.9 ± 2.3*
Red vastus
+E
25.6 ± 4.2
34.6 ± 9.9
143 ± 21
177 ± 14
14.2 ± 2.2
23.6 ± 3.2*
E
2.5 ± 1.4
2.7 ± 0.2
252 ± 27
293 ± 10
12.5 ± 2.1
20.9 ± 2.0*
White vastus
+E
43.6 ± 5.1
49.4 ± 15.8
62 ± 8
173 ± 21
4.9 ± 2.2
9.7 ± 3.6*
E
2.1 ± 2.0
1.6 ± 2.5
212 ± 14
298 ± 84
4.9 ± 1.6
10.1 ± 4.3*
Values are means ± SD; n = 6-7 animals/group.
TBARS, thiobarbituric acid reactive substances; +E, normal diet;
E,
vitamin E-free diet.
*
Significantly different from corresponding
control values at P < 0.05.
Significantly different
from corresponding +E values at P < 0.05. (Adapted from Refs.
27-29.)
In contrast, except for elevated levels in WV of ET animals,
high-performance liquid chromatography detection of malondialdehyde showed only trace accumulations in the muscles examined (see Refs. 27
and 29). No overt differences were observed in these animals with
regard to viability, training ability, or weight gain among the studied
groups (28).
No differences were reported in activity of the mitochondrial marker
enzyme SDH between +E and E specimens in any of the muscles in
either the trained or untrained groups (reported in Ref. 29). However,
SDH activity was enhanced in trained rats compared with untrained
specimens in all of the skeletal muscles examined
(P < 0.05; see Table 1).
Sample Western blots for HSP72 and HSC73 are presented in Fig.
1.
, vitamin E deprived; +, vitamin E fed; Std, 50 or
100 µg of standard Sol sample, depending on weights of subject muscle samples used.
Levels of HSP72 in +E untrained rats were found to be highest in Sol
muscle samples, with lower amounts found in Plant and RV and
undetectable amounts found in WV muscle samples. Levels of
HSP72 in E untrained rats followed this pattern (Figs. 1 and 2).
Vitamin E deprivation did not significantly alter HSP72 content in Sol, Plant, RV, or WV muscles compared with the same muscles in +E specimens.
After 8 wk of endurance training, trained animals exhibited increased
content of HSP72 compared with their untrained counterparts in all
muscles examined (Figs. 1 and 2). Of particular interest, however, was
the finding that HSP72 levels in samples from +ET animals were
significantly higher than those in samples from ET specimens in
both RV and WV muscles (Fig. 2).
The degree of increase in HSP72 levels after exercise training varied
between muscles; for the most part, HSP72 content appeared to rise in
inverse proportion to the level of HSP72 present in the nontrained
muscle. Hence, Sol had the highest HSP72 levels in both the +E and
E conditions but exhibited less than a twofold increase in HSP72
levels with training. In contrast, in WV, which had undetectable levels
of HSP72 without training, HSP72 rose dramatically after training in
both +ET and ET groups (Figs. 1 and 2). Results for RV
paralleled those of WV, showing at least fivefold increases in HSP72
levels with training over respective untrained specimens of similar
vitamin E status. Plant, despite having HSP72 levels similar to those
of RV under the nonexercised condition, showed only two- to threefold
increases in HSP72 content after exercise.
In contrast to HSP72, the constitutive isoform in this stress protein
family, HSC73, appeared for the most part to be refractory to the
effects of both vitamin E deprivation and exercise training (Figs. 1
and 3). HSC73 content did not vary
significantly in Plant and RV regardless of dietary or training status.
HSC73 content rose significantly in Sol in response to both vitamin E
deprivation (E > +E; ET > +ET) and training (+ET > +E). WV samples from E specimens showed lower HSC73 levels than
did WV samples of +E animals. After training, HSC73 content in WV of
ET animals remained significantly depressed despite having risen
to levels nearly comparable to those of +E and +ET. HSC73 content in WV of normal diet specimens did not differ between the control and trained
groups.
MHC-I content in WV was too low to measure in any of the four treatment
groups. In Sol, RV, and Plant, neither vitamin E deprivation nor
treadmill training appeared to alter MHC-I content in a statistically significant manner (Fig. 4).
A significant positive correlation between MHC-I content and HSP72
content (r = 0.51, P < 0.05) was found among muscle
samples of +E control animals when all muscles were considered together (Fig. 5). However, no such correlation was
found between MHC-I content and HSP72 content in any of the other
treatment groups. No correlation between MHC-I content and HSC73 in
muscle samples was found for any of the four treatment groups.
DISCUSSION
Previous studies have demonstrated that acute exercise is capable of
activating the heat-shock response (15, 17, 25), although the
exercise-associated mechanisms that initiate this response are unknown.
Some current interest is focused on the potential role of oxidant
stress as an initiator of the heat-shock response (25). Ushakova et al.
(30), for instance, found a reduced HSP70 heat-shock response in liver,
lung, brain, and spleen of antioxidant-supplemented mice; they suggest
this finding as evidence that heat shock is actually mediated by
oxyradical action. In the present study, a combination of vitamin E
deprivation and exercise training was employed in an effort to increase
intramuscular oxyradical action and to observe resultant changes in
HSP70 content. The dietary restriction used in this study reduced
vitamin E content to a magnitude (<10% of original content) that is
generally associated with increased lipid peroxidation and elevated
oxyradical levels (8). However, vitamin E deprivation alone was not a
sufficient stimulus to increase HSP72 content. In fact, HSP72 content
did not increase in response to exercise training to the same extent in
RV and WV of ET animals as it had in +ET animals.
If oxidative stress is a key initiator of HSP72 induction, it could be
argued that the reason vitamin E deprivation did not induce HSP72
content to rise was that it simply did not generate a sufficiently
oxidatively stressed environment. Such a finding was suggested by
measurements of malondialdehyde, a direct product of lipid
peroxidation, which was not found to increase in Sol, Plant, or RV
after either vitamin E deprivation or exercise (reported in Ref. 27).
In addition, in the present study, female rats were used, and their
higher levels of circulating estradiol may yield enhanced membrane
stability in vitamin E-deprived cells (1). However, the TBARS test, a
nonspecific indicator of lipid peroxidation, indicated lipid
peroxidation increased with vitamin E deprivation in all muscles other
than trained WV. In addition, with exercise training, TBARS increased
in Sol and +E Plant. It is notable that vitamin E mobilization appeared
to occur after exercise in +E Sol and +E Plant; during intensive
exercise, vitamin E has been shown to be mobilized and delivered to
blood plasma (22) putatively to counter increased oxidant stress on
blood cells by extruded reactive oxygen species (24). Such vitamin E
mobilization in these particular muscles, associated with increased TBARS levels, supports the possibility that oxidative stress did become
elevated with vitamin E deprivation and exercise. Whether vitamin E
deprivation directly increased oxyradical action is, unfortunately, a
difficult issue to resolve. Nevertheless, dietary manipulation of
antioxidant status can influence the HSP70 response to stress (30). The
fact that +ET specimens synthesized more HSP72 than their ET
counterparts also suggests some significant impact of nutritional
antioxidant status on intracellular function. Had vitamin E depletion
caused no effect, the pattern of HSP72 induction with exercise should
not have varied significantly between the two diet groups.
It is unlikely that this difference resulted from reduced exercise load
in the E animals; as each diet group underwent the same training
protocol, the body weights of both groups were similar after training
and both groups exhibited similar significant increases in muscle SDH
activity. Had the oxidative stress been sufficient to
activate heat-shock transcription factor, yet failed to alter actual
levels of the protein, as has been found in recent work (6), this would
merely explain the lack of HSP72 response to vitamin E deprivation
alone and not account for the difference observed with the +ET and
ET groups.
HSP72 has been argued to function in conjunction with its constitutive isoform, HSC73, to interact with nascent polypeptides in such a manner as to facilitate proper protein folding, transport, and assembly (5). Exercise training is accompanied by both mitochondrial proliferation and increased protein turnover as the muscle undergoing training is remodeled (3). Although such remodeling may be associated with increased HSP 72 content as evidenced in the rat undergoing compensatory hypertrophy (14), it is unlikely that HSP 72 is directly associated with the oxidative capacity of skeletal muscle (14, 16). HSP72 may act in the cytoplasm as an intracellular chaperone for components required for mitochondrial biogenesis (20); however, it is unclear from the present results whether increased HSP72 content is obligatory for mitochondrial proliferation.
In agreement with previously reported findings (14, 16), HSP72 expression in hindlimb muscle of +E untrained control animals correlated with MHC-I content (r = 0.51, P < 0.05; see Fig. 5); it was highest in MHC-I-rich Sol muscle, lower in Plant and RV, and undetectable in WV. Hence, under nonstressed or control conditions there appears to be a relationship between muscle fiber composition and HSP72 content. This might demonstrate that HSP72 plays a specific routine role in muscles rich in type I fibers. With regard to exercise training, however, the present results suggest either that this specific role is expanded to muscles composed of other fiber types or that HSP72 induction represents a more general adaptive response to the training program and hence muscle use. Although intensive training has been demonstrated to alter type I fiber proportion within some rat hindlimb muscles (9), the muscles examined in this study failed to show significant shifts in MHC-I content between sedentary and trained groups. Although this may reflect a reduced exercise intensity/duration in this study compared with that noted previously (9) or difficulty in resolving small shifts in MHC-I content, it would nevertheless be speculative to conclude that HSP72 induction with exercise training is responding primarily to shifts in MHC expression. Ornatsky et al. (21) reported a similar uncoupling of the relationship between MHC-I and HSP72 that exists in the skeletal muscle of sedentary animals after 10 days of chronic electrical stimulation of tibialis anterior. They noted a tenfold increase in the content of HSP72 with no concommitant change in the trace amounts of MHC-I found in tibialis anterior.
Waste metabolic heat generated during exercise will raise the
temperature of exercising muscles significantly; muscle temperatures of
44°C have been observed in trained rats run to exhaustion (4). Heat
is also a potent stimulus for HSP72 induction. Although heat alone may
explain some of the differences in HSP72 content between exercising and
nonexercising specimens (26), it is not a likely explanation for the
lower HSP72 content in the ET group compared with the +ET group.
Although core and muscle temperatures were not taken, it seems
reasonable that significant differences in heat generation did not
exist between these two groups, since they underwent identical training
protocols.
Impairment of cellular activities, such as overall protein synthesis,
has been associated with the products of membrane peroxidation (10) and
also with aging (31). In view of our finding of lesser HSP72 response
to training in E rats, a recent observation that aging blunts
HSP72 accumulation in tissues of heat-stressed rats (13) is
interesting. It has been reported that chronic vitamin E deficiency
that started early in the life of rodents can accelerate the onset of
aging phenomena and shorten life span (reviewed in Ref. 31). This
suggests the possibility that the lesser induction observed in the
ET group could occur simply as a consequence of premature aging
of the ET rats compared with the +ET rats. The explanation for
the lower HSP72 induction in muscle samples from the ET group
compared with the +ET group may alternatively lie in postexercise
protein handling within the muscle cells themselves. For instance,
inhibition of protein synthesis to spare cysteine for maintenance of
glutathione homeostasis has been demonstrated as a survival adaptation
in oxidatively stressed neurons (23). Indeed, a mechanism proposed by
Menon et al. (18), which suggests a role for HSP72 in inactivating
heme-regulated inhibitor, points to a potentially lower rate of protein
synthesis initiation in ET muscles compared with +ET muscles. A
smaller HSP72 pool in ET muscles would make more unbound
(active) heme-regulated inhibitor available than in +ET muscles,
leading to greater inhibition of initiation of protein synthesis.
Hence, one could speculate that a decreased rate of protein production,
accompanying oxidative damage, may diminish the need for stress
proteins in their chaperoning role in the ET group compared with
the +ET group. Increases in total protein turnover rate that accompany
training, in short, may be greater in the +ET group than in the
ET group, thus creating a greater demand for HSP72, since
protein synthesis would likely be less compromised (by membrane
instability, premature aging, or other means) in the vitamin E-rich
muscle cells compared with vitamin E-depleted ones.
In addition, in moments of intracellular stress, HSP72 appears to associate with ribosomes, perhaps transiently to await emergence of elongated polypeptides. This permits elongation to continue without a "backing up effect" that might decrease translation initiation (2). Thus if the total number of ribosomes actively translating protein is diminished as a consequence of lipid peroxidation, the need for synthesizing HSP72 in moments of stress decreases as well, even if the per ribosome rate of protein translation is itself undiminished. At this stage, however, such possibilities remain speculative, barring direct evidence of impairment of protein synthesis by these dietary and exercise stresses.
One finding that deserves closer examination is the observation that
those muscles with the highest control levels of HSP72 tended to
respond with the lowest increase after exercise training. Under in
vitro conditions, the heat-shock response to stress is diminished when
HSP levels have previously been elevated by a preconditioning stimulus
(19). A similar effect appears to occur in vivo in rat muscles
undergoing repetitive exercise stress. Hence WV and RV exhibited
greater than tenfold increases in most subjects, whereas Plant
exhibited a threefold increase in the +E specimens (none in the
E group) and the muscle with the highest initial levels, Sol,
demonstrated only a twofold increase. Nonetheless, an increase to a
similar final content of HSP72 across all examined muscles was
sustained throughout the 8-wk training period. This suggests that the
increased synthesis of HSP72 in skeletal muscle previously observed
after a single bout of acute exercise (15, 17, 25) may be part of some
more long-term adaptive process. Because increases in HSP72 after
exercise training appeared to be blunted in RV and WV under the
condition of vitamin E deprivation, we examined the content of HSC73 to
determine whether changes in the amount of this isoform could
compensate for the lack of response in HSP72 such that the total
chaperone content did not differ between the two diet groups. Clearly a
compensation did not occur; in RV, the skeletal muscle content of HSC73
was relatively constant regardless of the treatment group, whereas
HSC73 was actually reduced in WV under the condition of vitamin E
deficiency. Of the muscles that did not demonstrate a blunted response
for HSP72 to exercise training with vitamin E deprivation, Plant
exhibited no effect of training or diet on HSC73 content and HSC73
increased in Sol with training, vitamin E deficiency, and the
combination of these factors. The reasons for such differential
responses are unclear; however, observations of this nature may
eventually lead to further insight into the specific roles of these
proteins within the cell.
In contrast to HSP72, HSC73 was generally refractory to a training stimulus. This suggests that HSC73 probably plays a conserved and general role as a chaperone in mammalian skeletal muscle and tends to confirm that its role in the cell, although important, may not be an adaptive one.
ACKNOWLEDGEMENTS
This study was sponsored by grants from National Sciences and Engineering Research Council Canada to M. E. Houston and E. G. Noble.
FOOTNOTES
Address for reprint requests: E. G. Noble, Faculty of Kinesiology, Univ. of Western Ontario, London, Ontario N6A 5B7, Canada.
Received 5 June 1996; accepted in final form 17 July 1996.
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