Journal of Physiology
J Physiol (2003), 550.3, pp. 855–861
© The Physiological Society 2003
DOI: 10.1113/jphysiol.2003.040162
www.jphysiol.org
UCP3 protein regulation in human skeletal muscle fibre types
I, IIa and IIx is dependent on exercise intensity
Aaron P. Russell*†, Emmanuel Somm†, Manu Praz*, Antoinette Crettenand*, Oliver Hartley†,
Astrid Melotti†, Jean-Paul Giacobino†, Patrick Muzzin†, Charles Gobelet* and Olivier Dériaz *
*Clinique Romande de Réadaptation SUVA Care, Sion, Switzerland and †Département de Biochimie Médicale, Centre Médical Universitaire,
Université de Genève, Switzerland
It has been proposed that mitochondrial uncoupling protein 3 (UCP3) behaves as an uncoupler of
oxidative phosphorylation. In a cross-sectional study, UCP3 protein levels were found to be lower in
all fibre types of endurance-trained cyclists as compared to healthy controls. This decrease was
greatest in the type I oxidative fibres, and it was hypothesised that this may be due to the preferential
recruitment of these fibres during endurance training. To test this hypothesis, we compared the
effects of 6 weeks of endurance (ETr) and sprint (STr) running training on UCP3 mRNA expression
and fibre-type protein content using real-time PCR and immunofluorescence techniques,
respectively. UCP3 mRNA and protein levels were downregulated similarly in ETr and STr (UCP3
mRNA: by 65 and 50 %, respectively; protein: by 30 and 27 %, respectively). ETr significantly
reduced UCP3 protein content in type I, IIa and IIx muscle fibres by 54, 29 and 16 %, respectively.
STr significantly reduced UCP3 protein content in type I, IIa and IIx muscle fibres by 24, 31 and
26 %, respectively. The fibre-type reductions in UCP3 due to ETr, but not STr, were significantly
different from each other, with the effect being greater in type I than in type IIa, and in type IIa than
in type IIx fibres. As a result, compared to STr, ETr reduced UCP3 expression significantly more in
fibre type I and significantly less in fibre types IIx. This suggests that the more a fibre is recruited, the
more it adapts to training by a decrease in its UCP3 expression. In addition, the more a fibre type
depends on fatty acid b oxidation and oxidative phosphorylation, the more it responds to ETr by a
decrease in its UCP3 content.
(Resubmitted 30 January 2003; accepted after revision 1 May 2003; first published online 6 June 2003)
Corresponding author A. P. Russell: Clinique Romande de Réadaptation, Case Postale 352, Av. Gd-Champsec 90, 1951 Sion,
Switzerland. Email: [email protected]
Uncoupling protein 3 (UCP3) is a mitochondrial protein
that is expressed predominantly in skeletal muscle in both
rodents and humans (Boss et al. 1997). It is believed to play
a role in energy expenditure by uncoupling oxidative
phosphorylation, resulting in heat production without ATP
synthesis (Boss et al. 2000; Schrauwen et al. 2001). UCP3
mRNA exists as two isoforms, UCP3 long (UCP3L) and
short (UCP3S). UCP3S lacks the sixth transmembrane
domain and a purine nucleotide binding domain (Boss et
al. 1997), which are believed to be involved in the control
of UCP activity (Cannon & Nedergaard, 1985). Human
skeletal muscle consists of predominantly three muscle
fibre types: I, IIa and IIx (also known as IIb). The fibre
types are generally classified as slow or fast, depending on
their contractile characteristics (Schiaffino & Reggiani,
1996), which are a reflection of the expression of either the
slow or fast contractile protein isoforms of myosin heavy
chain (MHC), respectively. Type I fibres (slow) are recruited
at low stimulation frequencies and function oxidatively. In
contrast, type IIx fibres (fast) require high stimulation
frequencies and function glycolytically, while type IIa
fibres (fast) possess intermediate characteristics between
type I and IIx fibres. At the protein level, UCP3 is expressed
more in glycolytic type II and less in oxidative type I muscle
fibre types (Hesselink et al. 2001; Russell et al. 2003).
Exercise training is often used as an intervention to
modulate energy expenditure and substrate oxidation.
Cross-sectional studies have reported that the UCP3
mRNA (Schrauwen et al. 1999; Russell et al. 2002) and
protein (Russell et al. 2003) levels are lower in trained
cyclists when compared to healthy untrained controls. The
lower UCP3 content observed after training has been
suggested to be an adaptation that assists with the
endurance-exercise-induced increase in the efficiency of
aerobic ATP production (Schrauwen et al. 2001).
We have recently observed, in a cross-sectional study, that
the UCP3 protein is lower in all fibre types of endurancetrained cyclists as compared to healthy controls, with a
greater difference in the oxidative type I than in the
glycolytic type II fibres (Russell et al. 2003). Fibre-type
changes in skeletal muscle are regulated, at least in part, by
the frequency of motor nerve stimulation (Pette & Vrbova,
1992). This may explain our previous observation of a greater
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A. P. Russell and others
Journal of Physiology
difference in UCP3 in the type I as compared to the type II
fibres in endurance-trained cyclists as compared to healthy
controls, as type I fibres are recruited preferentially by
endurance training (Gollnick et al. 1974).
In the present study, we therefore aimed to understand
better the effect of exercise on human skeletal muscle
UCP3 expression by performing an intervention study and
by comparing two models of exercise training, endurance
versus high-intensity sprint training (ETr and STr,
respectively). The different intensities employed by endurance
and sprint exercise are known to recruit predominantly
different fibre types (Sale, 1987). Two groups of healthy
male subjects performed 6 weeks of either supervised ETr
or STr. Whole-muscle UCP3L and UCP3S mRNA, as well
as UCP3 protein levels in the type I, IIa and IIx fibre types
were measured in the vastus lateralis muscle of each
subject pre- and post-training.
METHODS
Subjects
Thirteen healthy and physically active males (mean ± S.D. age
31 ± 6 years, body mass 78 ± 9 kg, maximum oxygen uptake
(◊J,max) 54 ± 6 ml kg_1 min_1) underwent a muscle biopsy procedure
followed by a ◊J,max test. On a separate day, a 40 m sprint test was
performed. The subjects were matched for weight and ◊J,max and
placed into a group that completed 6 weeks of either ETr (n = 7)
or STr (n = 6). Training was performed three times per week
under the supervision of a fitness instructor. A second muscle
biopsy procedure and the same exercise tests were completed
again in the same order, following the training programmes. Each
subject was informed as to the requirements of the study before
giving his written consent to participate. The study was approved
by the ethics committee of the local medical society and conformed
with the guidelines of the Declaration of Helsinki. These subjects
are different from those who participated in our previous work
(Russell et al. 2003).
Muscle sampling, treatment and analysis
Skeletal muscle samples were obtained under local anaesthesia
(xylocaine, 1 % plain) from the belly of the vastus lateralis muscle
using a percutaneous needle biopsy technique (Bergstrom, 1975)
that was modified to include suction. A single incision was made
in the skin and two muscle samples were taken from a single
insertion of the biopsy needle. After the first biopsy cut, the needle
was rotated and a second cut was performed. Each muscle sample
weighed between 50 and 80 mg. One muscle sample was mounted
in embedding medium and frozen in isopentane that had been
cooled to its freezing point. The other muscle sample was frozen
immediately in liquid nitrogen and used for RNA extraction.
Measurement of oxygen consumption
◊J,max was measured using a Quark B2 metabolic cart (Cosmed,
Rome, Italy) while subjects were running on a treadmill (Technogym
Runrace, Gambettola, Italy). The subjects began running at
7.2 km h_1 with a 1 % gradient. The speed was increased by
1.8 km h_1 every 3 min until the subject could not maintain the
speed. The duration of the tests was between 10 and 15 min. Heart
rate (Polar) and oxygen consumption were measured continually
throughout the test. ◊J,max was calculated as the highest average
value over a 30 s period.
J Physiol 550.3
Fat-free mass
Fat-free mass was determined by plethysmographic measurement
of body volume using the BOD POD Body Composition System
(LIM, Concord, USA; Dempster & Aitkens, 1995). This device uses
the relationship between pressure and volume to derive the body
volume of a subject seated inside a fibreglass chamber.
The 40 m sprint test
On a separate day, after a 15–20 min warm-up consisting of light
jogging, accelerations and stretching, subjects performed three
maximal 40 m sprints. Each test was separated by approximately
5 min of recovery. The times were recorded using photoelectric
cells. Subjects started from a standing position and commenced
each sprint voluntarily.
Training programme
Endurance. The ETr programme comprised three supervised
sessions per week, which included two interval sessions separated by
a constant-intensity session. Each session commenced with a warmup consisting of approximately 10 min of light running followed by
stretching. The interval sessions consisted of 5–6 intervals at an
individual intensity corresponding to 70–80 % of ◊J,max. For
example, during the 1st week, 5 w 70 % repetitions were performed,
during the 2nd week this was increased to 6 w 70 %, and during the
3rd week to 5 w 75 %. This pattern was followed so that during week
6 the subjects were completing 6 w 80 % repetitions. A 1 min
recovery was allowed between each test at an intensity of 50 % of
◊J,max. The duration of these intervals ranged between 1 and 3 min
for each subject. All intensities were controlled by individual heart
rates, which were measured throughout the sessions, using a Polar
heart-rate monitor. The constant-intensity session consisted of
running for 40 min at an intensity of 60 % of ◊J,max.
Sprint training. The STr programme consisted of three supervised
sessions per week. Each session comprised 4–8 repetitions covering a
distance of 40–80 m, referred to as one series (Dawson et al. 1998).
The warm-up for each session was the same as mentioned above.
The number of series completed during each session was between
four and six, so that each subject completed between 16 and 24
sprints per session during the 1st week. This was gradually increased
so that all subjects completed 40 sprints during week 6. A 4–6 min
rest was allowed between each series. The intensities for each sprint
were between 90 and 100 % of maximal speed. All intensities were
controlled by individual heart rates, which were measured
throughout each session using a Polar heart-rate monitor.
RNA extraction and quantitative RT-PCR
Total RNA was extracted from ~15 mg of frozen muscle using the
Trizol reagent and the protocol provided by the manufacturers
(Invitrogen, Basel, Switzerland). Oligo-dT primed first-strand
cDNA was synthesised from 2 mg of total RNA (SuperScript III
Reverse Transcriptase, Invitrogen). Real-time PCR was performed
using a Lightcycler rapid thermal cycler system and the LightcyclerDNA Master SYBR Green I mix, as per the manufacturer’s
instructions (Roche Diagnostics, Rotkreuz, Switzerland). The PCR
conditions for the amplification of the UCP3L and UCP3S isoforms
and b-actin mRNA consisted of 2 min of denaturing at 95 °C,
followed by 30 cycles with denaturing at 95 °C for less than 1 s. For
the genes mentioned above, annealing was performed at 56, 58 and
58 °C for 6 s, and extension at 72 °C for 14, 10 and 22 s. It has been
shown that the expression of b-actin mRNA does not change with
training (Schrauwen et al. 1999; Russell et al. 2002) and it was
therefore used as a control to account for any variations due to the
efficiency of the reverse transcription and PCR.
Journal of Physiology
J Physiol 550.3
UCP3 regulation by exercise
Immunofluorescence
An immunofluorescence technique was used to measure human
UCP3 (hUCP3) protein content in type I, IIa and IIx muscle
fibres, as reported previously (Hesselink et al. 2001; Russell et al.
2003). Muscle fibre composition was determined by counting the
number of positive fibres stained with antibodies, obtained from
the Development Studies Hybridoma Bank, the University of
Iowa, raised against the human slow type I (A4.84) and fast IIa
(N2.261) MHCs, respectively (Hesselink et al. 2001; Russell et al.
2003). The muscle fibres that were not stained were deemed to be
type IIx fibres. Optimal serum dilution of the hUCP3 antibody
was determined and used at 1:200. For each subject, four muscle
sections obtained from the pre-training biopsy procedure and
four muscle sections obtained from the post-training biopsy
procedure were placed on the same glass slide. Two sections from
the pre- and two sections from the post-training biopsy procedures
were incubated without the primary antibody and were used as
negative controls. The other two sections from the pre- and posttraining biopsy procedures were incubated with both the primary
and secondary antibodies and used as the experimental samples.
This procedure was performed in duplicate. All muscle sections
were analysed at the same time. Sections were viewed and
photographed using a Zeiss Axiophot I microscope mounted with
an Axiocam colour CCD camera. The specific fluorescence within
each fibre was quantified using the Zeiss KS400 V3.0 program.
857
testing was performed in the stratified analysis (Stanton & Slinker,
1990; Selvin, 1995). The statistical power was > 0.75 for all analyses,
indicating that any non-significant results were signs of no
differences rather than a consequence of the small sample size. All
values are reported as means ± S.D.
RESULTS
Neither ETr nor STr significantly changed body fat-free mass
(ETr: pre = 66 ± 6 kg, post = 67 ± 7 kg; STr: pre = 64 ±
4 kg, post = 64 ± 3 kg) or fat mass (ETr: pre = 11 ± 6 kg,
post = 11 ± 6 kg; STr: pre = 14 ± 8 kg, post = 13 ± 8 kg).
Table 1 presents pre- and post-training results for ◊J,max
(ml kg_1 min_1) and 40 m sprint time for both the ETr and
STr groups. There was no difference in either of the variables
between the ETr and STr groups before training (P > 0.05).
Both ETr and STr increased ◊J,max, by 9 and 7 %, respectively
(P < 0.05). While ETr did not change 40 m sprint time
(P > 0.05), STr resulted in a 2.6 % decrease (P < 0.05).
Figure 1 presents pre- and post-training results for fibretype composition. After ETr, the percentage of type I muscle
fibres increased by 18 % (P < 0.01), while that of IIa and
Validation of the hUCP3 antibody
A hUCP3 antibody (Sigma) was validated for the immunofluorescence technique using L6 cells transduced with hUCP3
using a lentivirus-based vector (Naldini et al. 1996). The three
plasmids required for vector production were kindly provided by
Dr Didier Trono, University of Geneva (Zufferey et al. 1997).
Using the immunofluorescence technique described above, a
fluorescent signal was observed in the hUCP3-transduced L6 cells.
No signal was observed in the wild-type cells.
Statistical analysis
Student’s two-tailed unpaired t tests were used to compare subject
characteristics and total muscle UCP3 mRNA and protein
expression between the ETr and STr groups before training. Paired
t tests were used to compare the subject characteristics and total
muscle UCP3 expression pre- and post-training for both the ETr
and STr groups, respectively. A two- (training status (pre vs. post)
between-factor) w three (fibre types-within factor)-factor ANOVA
was used to compare the influence of training status and fibre type
on UCP3 protein expression for both the ETr and STr groups.
Also, a two- (training group (ETr vs. STr) between-factor) w three
(fibre types-within factor)-factor ANOVA was used to compare
the influence of training intensity and fibre type on UCP3. For this
analysis, the pre-training UCP3 values were used to normalise the
post-training values. When the ANOVAs revealed significant
interactions, stratified analyses were used to locate the significant
differences. While the overall a level for the ANOVA was set at
0.05, the Sharpened Bonferroni method was used to adjust the
individual a level to significance of P < 0.0167 when multiple
Figure 1. Muscle fibre-type composition expressed as the
change in the percentage of skeletal muscle MHC
isoforms with ETr (Endurance) and STr (Sprint)
Black bars, pre-training values; open bars, post-training values;
†significantly different from the same fibre in the respective
training group (P < 0.01); *significantly different from the same
fibre in the respective training groups (P < 0.05); ‡significantly
different from the same fibre in the ETr group post-training
(P < 0.05).
A. P. Russell and others
Journal of Physiology
858
Figure 2. Effect of ETr and STr on muscle total UCP3 mRNA and protein content
Total UCP3 mRNA (A) and protein content (B) before (Pre) and after (Post) ETr and STr. The values are
expressed as means ± S.E.M. *Significantly different from pre-training value within the same training group
(P < 0.05).
Figure 3. Effect of ETr and STr on UCP3L and UCP3S mRNA isoform expression
UCP3L (A) and UCP3S (B) mRNA isoform expression before and after ETr and STr. The values are expressed
as means ± S.E.M. *Significantly different from pre-training value, within the same training group (P < 0.05).
J Physiol 550.3
Journal of Physiology
J Physiol 550.3
UCP3 regulation by exercise
IIx fibres decreased by 12 % and 6 %, respectively (P < 0.05).
For each subject, a total of 350 ± 40 fibres were counted
both pre- and post-training: type I, 174 ± 50 and 238 ± 55,
respectively; type IIa, 111 ± 36 and 74 ± 38, respectively;
type IIx, 64 ± 53 and 35 ± 29, respectively. After STr, the
percentage of type I and IIx fibres decreased by 7 % and
3 %, respectively (P < 0.05), while the percentage of type
IIa fibres increased by 10 % (P < 0.05). For each subject, a
total of 377 ± 32 fibres were counted both pre- and posttraining: type I, 226 ± 22 and 194 ± 22, respectively; type
IIa, 121 ± 45 and 158 ± 44, respectively; type IIx, 32 ± 28
and 22 ± 18, respectively.
Total UCP3 mRNA and protein expression were not
different in the two pre-trained groups (P > 0.05). The ETr
and STr programmes exhibited a reduction in UCP3 mRNA
expression, by 65 and 50 %, respectively (P < 0.001; Fig. 2A).
The reduction in total UCP3 mRNA by ETr and STr was
also followed by a reduction in total UCP3 protein content,
by 30 and 27 %, respectively (Fig. 2B).
859
therefore upon the frequency of muscle contraction and
the fibre type recruited.
One of the adaptations to ETr is an increase in ◊J,max (Jones
& Carter, 2000). Consistent with previous reports (Jones &
Carter, 2000), our ETr programme increased ◊J,max by 9 %.
Endurance training at an exercise intensity of approximately
40–50 % of ◊J,max induces a low rate of repeated muscle
contraction, which recruits predominantly the slow-twitch
type I muscle fibres. Type IIa fibres start to be recruited
when exercise intensities increase to between 40 and 75 %
of ◊J,max. In the present study, consistent with previous
reports (Fitts & Widrick, 1996), ETr increased the percentage
number of type I muscle fibres and decreased the percentage
number of type IIa and IIx fibres, as measured by MHC
isoform expression.
UCP3L and UCP3S mRNA expression were not different in
the two groups pre-training (P > 0.05). ETr reduced UCP3L
and UCP3 s mRNA by 54 and 75 %, respectively (P < 0.01).
STr reduced UCP3L and UCP3S mRNA by 37 and 77 %,
respectively (P < 0.01; Fig. 3). There was no difference in
UCP3L and UCP3S mRNA expression between the ETr and
STr groups post-training (P > 0.05). ETr and STr reduced
UCP3S mRNA significantly more than UCP3L mRNA
(P < 0.01).
UCP3 protein expression in the different fibre types was
similar in the two groups pre-training (P > 0.05). ETr
reduced UCP3 protein content in type I, IIa and IIx muscle
fibres by 54 (P = 0.005), 29 (P = 0.008) and 16 % (P = 0.002),
respectively. STr reduced UCP3 protein content in type I,
IIa and IIx muscle fibres by 24 (P = 0.002), 31{ (P = 0.002)
and 26 % (P = 0.006), respectively (Fig. 4A). Figure 4B
shows the reduction in UCP3 in all fibre types of the ETr
and STr groups, with the values expressed as the posttraining:pre-training UCP3 ratio. The fibre-type reductions
in UCP3 due to ETr, but not STr, were significantly
different from each other, with effects being greater in type
I than in type IIa (P = 0.001) and in type IIa than in type IIx
fibres (P = 0.015). In addition, UCP3 was reduced more in
the type I fibres of ETr compared to STr (P = 0.009) and
less in the type IIx fibres (P = 0.002).
DISCUSSION
Exercise promotes motor nerve stimulation and consecutive
contraction of skeletal muscle. The intensity of exercise
controls the frequency of motor nerve stimulation and
therefore determines which muscle fibres are recruited
(Sale, 1987). The present findings show that the changes in
UCP3 protein content in the different skeletal muscle fibre
types are dependent upon the intensity of exercise and
Figure 4. Effect of ETr and STr on UCP3 protein content in
the different muscle fibre types
A, UCP3 protein content in the different fibre types before and
after ETr and STr. Black bars, pre-training values; open bars, posttraining values. *Significantly different from the same fibre, pretraining, in the respective training group (P < 0.05). B, changes in
the levels of UCP3 in the different fibre types, expressed as a posttraining:pre-training ratio. Black bars, ETr group; open bars, STr
group. ‡Significantly different from each other within the ETr
group (P < 0.05). §Significantly different from the same fibre type
in the ETr group (P < 0.05). The values are expressed as
means ± S.E.M.
Journal of Physiology
860
A. P. Russell and others
High-intensity sprint exercise performed at intensities
above 90 % of ◊J,max induces a high rate of repeated muscle
contractions, which recruits all fibre types (Sale, 1987).
During such high-intensity exercise and high power
output, the rate of ATP hydrolysis is correspondingly high.
This is provided predominantly by the contraction of the
fast-twitch type II muscle fibres, which contain the fast
isoform of the MHC; however, at these intensities the type
I fibres are also recruited (Sale, 1987). The STr programme
used in this study is that described by Dawson et al. (1998).
Consistent with previous reports, STr (Dawson et al.
1998), but not ETr, decreased 40 m sprint time. This
enhanced physical performance may be, at least in part,
attributed to the adaptation of the skeletal muscle fibres to
the STr; however, neurological adaptations may also have
contributed to the increase in power (MacDougall et al.
1991). As already shown (Jansson et al. 1990; Esbjornsson
et al. 1993; Andersen et al. 1994), STr induced a decrease in
the percentage of type I and IIx muscle fibres and an
increase in IIa muscle fibres. The changes in performance
variables such as ◊J,max and 40 m sprint time, as well as
changes in the percentage of the type I, IIa and IIx MHC
isoform contents, demonstrate that the ETr and STr
programmes implemented in the present study induced
the expected specific effects of recruitment of the three
muscle fibre types.
The main objective of the present study was to investigate
the effect of muscle fibre recruitment frequency, as
stimulated by ETr and STr, on the regulation of UCP3
expression. During endurance exercise, UCP3 activity
should decrease performance by uncoupling oxidative
phosphorylation. This would then require an increase in
mitochondrial respiration to maintain a high ATP:ADP
ratio and therefore induce early fatigue. After endurance
exercise, a greater UCP3 activity may reduce the rate of
phosphocreatine resynthesis, lactate removal and the
restoration of muscle and blood oxygen stores. Theoretically,
UCP3 activity should not affect performance during sprint
exercise, as sprint exercise depends mostly on phosphocreatine degradation and anaerobic glycolysis. After sprint
exercise, an increased UCP3 activity may reduce the rate of
phosphocreatine resynthesis.
Surprisingly, ETr and STr downregulated similarly UCP3
mRNA and protein levels as well as the two UCP3 isoform
levels. It is noteworthy that both ETr and STr downregulated the expression of UCP3 mRNA twofold more
than the UCP3 protein, supporting the suggestion of posttranscriptional regulation (Giacobino, 2001). Furthermore,
ETr and STr downregulated UCP3S more than UCP3L. At
present it is unknown if the two UCP3 isoforms have
different physiological functions. However, it has been
postulated that the absence of the sixth transmembrane
domain in UCP3S may render this isoform inactive (Boss et
al. 1997). The mechanism and the biological consequence
J Physiol 550.3
of the greater downregulation of UCP3S as compared to
UCP3L with exercise training is unknown. Additional work
must be carried out to clarify whether these two isoforms
are active and, if so, what are their respective roles.
The only differential effect of ETr as compared to STr was
observed at the level of UCP3 expression in the different
fibre types. Indeed, as summarised in Fig. 4B, in which the
results are expressed as training-induced percentage changes
in UCP3 expression, ETr effects are associated with the
fibre-type oxidative capacity, whereas STr affects similarly
all three fibre types. As a result, STr reduces UCP3
expression significantly less in fibre type I and significantly
more in fibre type IIx, than ETr. An explanation for this
observation would be that the more a fibre is recruited, the
more it adapts to training by a decrease in its UCP3
expression. Indeed, ETr recruits predominantly type I
fibres, whereas STr recruits similarly all fibre types. It is
noteworthy that the more a fibre type depends on fattyacid b oxidation and oxidative phosphorylation, the more
it responds to ETr by a decrease in its UCP3 content.
Indeed, this type of training has larger effects on type I than
on type II fibres. Furthermore, the smaller effects of STr, as
compared to ETr, on the expression of UCP3 in type I
fibres may be due to the fact that STr increases the glycolytic
capacity of these fibres.
A reduced UCP3 content after training may be an adaptation
that assists, at least in part, with an improvement in
performance. For the endurance athlete, a reduced mitochondrial uncoupling would increase the efficiency of
oxidative phosphorylation, which would enable performance
at a higher intensity, while for the sprint athlete it would
increase the rate of phosphocreatine resynthesis after an
intensive exercise bout (Bogdanis et al. 1996) for the same
oxygen consumption.
Conclusions
Both ETr and STr downregulated UCP3L and UCP3S
mRNA expression and protein content. Irrespective of
training intensity, UCP3S was reduced more than UCPL.
ETr and STr reduced the UCP3 protein content in all
fibres. The ETr group exhibited a preferential fibre-type
downregulation of UCP3 protein, with the greatest reduction
occurring in the type I, less in the type IIa and the least in
the type IIx muscle fibres. In contrast, this was not
observed after STr, as the relative UCP3 downregulation
was similar in all fibre types. Fibre-type regulation of the
UCP3 protein after ETr and STr reflects the fibre-type
recruitment pattern stimulated by the recruitment frequency
of the respective training intensities.
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Acknowledgements
The monoclonal antibodies directed against adult human and
MHC isoforms (referred to as A4.84 and N2.261, respectively)
used in the present study were developed by Dr Blau and were
obtained from the Development Studies Hybridoma Bank, under
the auspices of the NICHD and maintained by the University of
Iowa, Department of Biological Sciences, Iowa City, IA 52242,
USA. Dr Russell was supported by grants from the Helen M.
Schutt Trust, Office Féderal du Sport Macolin, Fonds Eugène
Rapin, the Fondation du Centenaire de la Société Suisse
d’Assurances Générales sur la Vie Humaine Pour la Santé
Publique et les Recherches Médicales. This work was also
supported by the Swiss National Science Foundation grant no.
31–54306.98 and the Fondation Suisse de Recherche sur les
Maladies Musculaires. We thank Sigma for providing us with the
hUCP3 antibody. We would also like to thank the volunteers for
their commitment and enthusiasm, Ingrid Tofor and Chantal
Ansiaux for their assistance with the muscle biopsy sampling and
Patrick Crettenand for his expertise in supervising all of the
training sessions.