1 Department of Life Sciences (Sports Sciences), University of Tokyo, Tokyo 153, Japan; and Departments of 2 Kinesiology and 3 Biology, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
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ABSTRACT |
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We examined the
postnatal changes (days 10, 36, 84, 160, 365) of
monocarboxylate transporters (MCT)1 and MCT4 in rat heart and soleus
muscle. In the heart, MCT1 protein and mRNA remained unaltered from
day 10 until 1 yr of age. Both MCT4 protein and mRNA in the
heart were detected at 10 days of age, but the MCT4 protein and
transcript were not detected thereafter. In the soleus muscle, MCT1
protein (+38%) and mRNA (+136%) increased during the first 84 days
and remained stable until 1 yr of age. In contrast, soleus MCT4 protein
decreased by 90% over the course of 1 yr, with the most rapid decrease
(60%) occurring by day 84 (P < 0.05). At
the same time, MCT4 mRNA was increased by 74% from days 10 to 84 (P < 0.05), remaining stable
thereafter. In conclusion, developmental changes in MCT transport
proteins are tissue specific and isoform specific. Furthermore, it
appears that MCT1 expression in the heart and MCT1 and MCT4 expression
in the soleus are regulated by pretranslational processes, whereas
posttranscriptional processes regulate MCT4 expression in the soleus muscle.
monocarboxylate transporters; protein; messenger ribonucleic acid; phosphofructokinase; citrate synthase; glucose transporter 4
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INTRODUCTION |
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THE MOVEMENT OF LACTATE across the plasma membrane of heart and skeletal muscle occurs via a transport system involving carrier proteins (16, 19). There appears to be a family of seven monocarboxylate transporter (MCT) isoforms (MCT1-7) that can transport a variety of monocarboxylates (see Ref. 16 for review). Tissue-specific expression has been shown for some of these MCTs, although several are coexpressed in heart and skeletal muscle (27, 38). The transport kinetics of the various MCT proteins for different monocarboxylates as well as the regulation of MCT isoform expression remain to be clarified.
MCT1 is present in heart and skeletal muscles, as well as in other tissues (2, 18, 24, 25). In general, in adult rats, MCT1 is present in greater quantities in heart than in skeletal muscles (2, 4, 25), whereas among different types of rat skeletal muscles, the expression of MCT1 is highly correlated with their oxidative capacities (25). Increasing the oxidative capacities of muscles by chronic electrical stimulation increases their MCT1 content (4, 24). Exercise training increases MCT1 in both heart and muscle (2). In these studies, the changes in lactate uptake rates parallel the changes in MCT1 in heart and muscles (2, 24). Indeed, we have recently shown (5) that an increase in lactate uptake by muscle occurs when only MCT1, but not MCT4, protein levels are increased.
Thus far, much less is known about MCT4. In human heart, MCT4 is detectable, but in hearts obtained from rats it is not (38). Skeletal muscle expresses both MCT1 and MCT4 (4, 5, 38); however, MCT4 is present in very low concentrations in the slow-twitch oxidative soleus muscle from mature animals, whereas it is very abundant in fast-twitch oxidative glycolytic muscles (4, 38). MCT4 concentrations are also positively correlated with the content of fast-twitch glycolytic muscle fibers in different rat muscles (4), and among rat hindlimb muscles with different metabolic capacities there is an inverse relationship between the MCT1 and MCT4 content (4). Finally, MCT1 has a greater affinity for lactate [Michaelis-Menten constant (Km) ~4 mM] (6) than does MCT4 (Km ~30 mM) (11).
On the basis of the relationships between MCT1 and the oxidative capacity of muscle fibers, we have proposed that MCT1 expression may reflect the capability to oxidize lactate (24, 25). Along similar lines, we have proposed that the relationship between MCT4 and the glycolytic capacity of muscle fibers may reflect the muscle's requirement for lactate efflux (4, 38). This view is also supported by others (11).
During early postnatal life, marked alterations occur in substrate metabolism in heart and soleus muscle. In the rabbit and rat hearts, there is a marked reduction in the rates of glycolysis and a sharp increase in palmitate oxidation in the first 7-20 days of life (13, 22). In soleus muscle during the first 12 wk of life, there are changes in oxidative capacity, muscle fiber composition, muscle fiber area, and muscle capillarization (31, 32). However, all of these changes in muscle do not occur at the same time. For example, soleus muscle succinate dehydrogenase activity attains a maximum at 28 days of age, which is maintained at least up to 84 days of age, whereas muscle capillarization attains a maximum 2 wk later, at 6 wk, and soleus muscle fiber composition and the areas of type I and type IIa fibers increase for at least 12 wk, albeit at different rates (31, 32). Thus, clearly, muscle architecture, substrate delivery, and metabolic capacities do not change in a tightly coordinated pattern during the first 12 wk of life in the rat.
During the life span of the rat (25 mo), changes in the substrate
transporters in muscle and heart have been examined only for GLUT-1 and
GLUT-4. These studies have shown that, in the early postnatal period
(days 1-16), GLUT-1 decreased rapidly in skeletal muscle and heart (30), whereas GLUT-4 increased in both
tissues (30, 34). Importantly, the rates of change in
GLUT-1 and GLUT-4 differed, and the rates of change of each glucose
transporter isoform differed when these were compared in muscle and
heart (30, 34). In some skeletal muscles, but not all,
GLUT-4 content is reduced in old (24-25 mo) compared with young
(2-3 mo) rats (3, 8, 15, 20), although these
decreases, when observed, occurred somewhere between 1 and 10 mo of age
(15). Collectively, the foregoing studies indicate that
changes in substrate transporters such as GLUT-1 and GLUT-4 occur
rapidly in postnatal life, and the more gradual changes in GLUT-4, when
they are observed, are not closely related to changes in muscle
metabolism or architecture.
Whether there are age-dependent changes in the MCT1 and MCT4 in heart and/or muscle is not known. In view of the changes in the metabolic capacities of both the heart and soleus muscle during the early postnatal period, it can be expected that there may also be marked changes in MCT1 and MCT4 in these tissues. However, beyond this period, there may also be further changes in the expression of these MCTs that are not necessarily tightly associated with changes in the metabolic capacities of heart and soleus muscle, as has been shown for GLUT-4 (15). We hypothesized that, as the heart and soleus muscle become more dependent on oxidative metabolism, particularly early in life, MCT1 would be increased, whereas MCT4 would concomitantly be reduced. We also hypothesized that MCT4 in muscle might be reduced further after the early postnatal period, because lactate release from muscle is reduced during the first year of life (14). Therefore, in the present study we have examined, in rat soleus muscle and heart, the tissue-specific changes in MCT1 and MCT4 proteins, as well as their transcripts, over a 1-yr period (days 10-365). We also compared changes in GLUT-4 protein and mRNA in these studies with previous reports (10, 34, 36) as a positive control for the present studies.
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METHODS |
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Animals. Male Sprague-Dawley rats were used. Ethical approval was obtained for this work from the committee on animal care at the University of Waterloo. Animals were bred in the University of Waterloo animal care facilities. They were handled daily and were allowed free access to water and food ad libitum. Soleus muscles and the hearts of the rats were taken while they were anesthetized (Somnotol, ip). Tissues were obtained in neonatal rats (day 10) just after weaning at 28 days [i.e., days 33-40 (mean = 36)], after sexual maturity (>42 days) had occurred [i.e., days 80-88 (mean = 84)], and during adult life [i.e., days 143-170 (mean = 160) and at 1 yr of age].
Enzyme analyses. Activities of phosphofructokinase (PFK) and citrate synthase (CS) in heart and soleus muscles were analyzed using standard procedures (23).
Western blotting of MCT1 and MCT4. Proteins were isolated from soleus muscles and the heart and detected using Western blotting, as we have previously described in detail (4, 5, 24, 25, 38). MCT1 and MCT4 antibodies for these purposes were a gift from from Dr. A. P. Halestrap (Dept. of Biochemistry, University of Bristol, Bristol, UK). GLUT-4 antibodies were obtained from East-Acres Biologicals (Southbridge, MA). For each set of Western blots, data from hearts and soleus muscles at each time point were included, as well as a rat heart standard. This permitted normalization of the data to the rat heart standard across the different blots. MCT1, MCT4, and GLUT-4 protein band densities were obtained by scanning the blots on a densitometer connected to a Macintosh LC computer with appropriate software.
Northern blot analysis. mRNA determinations were made as we (4, 5) have described previously. Briefly, 3 µg of total RNA were used for electrophoresis on 1.2% formaldehyde agarose gels (29) and then transferred to positively charged nylon membrane (Boehringer Mannheim, Laval, QC, Canada). The Northern blots were ultraviolet cross-linked with a GS Gene linker (Bio-Rad, Mississauga, ON, Canada). Human GLUT-4 cDNA was obtained from American Type Culture Collection (Rockville, MD). MCT1 cDNA and MCT4 cDNA were a gift from from Dr. A. P. Halestrap.
A 1.9-kb fragment containing the coding sequence of MCT1 cDNA was isolated from the full length (3.3 kb) MCT1 cDNA by digestion with the EcoRI restriction enzyme (17) and subcloned into the EcoRI restriction enzyme site of pBluescript (KS). The orientation was checked by digestion with HindIII restriction endonuclease. Template DNA was linearized with XbaI restriction enzyme, and digoxigenin (DIG)-labeled antisense MCT1 riboprobe was generated by in vitro transcription with T3 RNA polymerase. MCT4 cDNA was originally subcloned into BamHI/ApaI restriction enzyme sites of pBluescript (38). DIG-labeled antisense MCT4 riboprobe was generated by digestion of the template DNA with XbaI restriction enzyme and in vitro transcription with T7 RNA polymerase. GLUT-4 cDNA was subcloned into pGEM-4Z. A 2-kb-long DIG-labeled GLUT-4 antisense riboprobe was generated by digestion of the template DNA with BamHI restriction endonuclease and in vitro transcription with T7 RNA polymerase. The ingredients for RNA transcription included 1-2 µg of DNA template plus the NTP mix [in nM: 2.5 CTP, 2.5 GTP, 2.5 ATP, 1.625 UTP (Promega, Madison, WI) and 0.875 Dig-11 UTP (Boehringer Mannheim)], 20 dithiothreitol (Promega), and 1 U/µg template DNA of RNase Inhibitor (Promega) and 1× RNA polymerase buffer [5× buffer: 400 mM Tris · HCl pH 7.5, 60 mM MgCl2, and 20 mM spermidine-HCl (Promega)] maintained at room temperature. The appropriate RNA polymerase [T3 or T7 RNA polymerases (Boehringer Mannheim)] was added (Data analyses. The data were analyzed with analyses of variance. Significance was determined with Fischer's least significant differences post hoc test. All data are expressed as means ± SE.
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RESULTS |
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During the course of the study, body weight of the rats increased
progressively from 21.7 ± 0.8 g at 10 days of age to
515.5 ± 9.0 g at 1 yr of age (P < 0.05;
Fig. 1A). Soleus weights
(P < 0.05) and heart weight (P < 0.05) were also increased during this period (Fig. 1B).
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Enzyme activities.
In the heart, neither PFK nor CS activities were altered over the
course of 1 yr (P > 0.05; Fig.
2A). In soleus muscle, CS activity was increased ~40% from days 10 to 36 (P < 0.05; Fig. 2B). In contrast, there was
a marked decrease in PFK activity from days 10 to
36 (38% decrease, P < 0.05; Fig. 2A).
Thereafter, PFK activity was not further altered in this muscle.
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Age-related changes in MCTs.
Data in the present study were normalized to the results obtained on
day 10 (100%) in both soleus muscle and the heart.
Representative MCT1 and MCT4 Western and Northern blots obtained from
animals ranging in age from 10 to 365 days of age are shown in Figs.
3 and 4.
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Heart MCT1 and MCT4.
In the heart, the MCT1 protein content was not altered (<10% change)
from day 10 until 1 yr of age (P > 0.05;
Fig. 5A). Similarly, MCT1 mRNA
abundance in the rat heart was not altered (P > 0.05; Fig. 5B). In contrast, MCT4 protein was detectable only at
10 days of age, but not thereafter (Fig.
6A). Similarly, MCT4 mRNA transcripts were also detected only at 10 days of age (Fig.
6B).
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Soleus MCT1 and MCT4. In the soleus muscle, MCT1 increased 38% from day 10 until 84 days of age. (P < 0.05; Fig. 5A), with no changes thereafter. During this same 84-day period. MCT1 mRNA was also increased (136%; P < 0.05; Fig. 5B).
Soleus muscle MCT4 protein increased slightly (15%) from days 10 to 36 (P = 0.05). By 84 days, MCT4 protein was reduced by 60% from concentrations observed at day 10 (P < 0.05; Fig. 6A). There was then a further decrease until 1 yr of age when MCT4 fell to 10% of that observed on day 10 (P < 0.05). Thus, over the course of almost 1 yr (days 10-365), MCT4 concentrations were reduced by 90% (P < 0.05; Fig. 6A). Although MCT4 protein content was decreasing in soleus muscle, MCT4 mRNA increased. From day 10 until 84 days of age, MCT4 mRNA was increased by 74% (P < 0.05; Fig. 6B). Thereafter, the MCT4 mRNA abundance remained constant until 1 yr of age (Fig. 6B).Heart and soleus muscle GLUT-4.
GLUT-4 protein increased rapidly from days 10 to
36 in heart (P < 0.05) and soleus muscle
(P < 0.05; Fig. 7). In
heart, a plateau was attained by day 36, whereas in soleus
this was not observed until day 84. Heart and soleus muscle
GLUT-4 transcripts also increased rapidly from days 10 to 36 (P < 0.05). In soleus muscle, a
plateau was attained by 160 days, but in the heart, GLUT-4 mRNA was
seen to increase from days 36 to 88 (P < 0.05) and from day 88 to 1 yr of age
(P < 0.05; Fig. 7).
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DISCUSSION |
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This is the first study to examine changes in MCT1 and MCT4 in
heart and soleus muscles over the course of a 1-yr period. This time
frame included the early postnatal period (day 10), the
immediate postweaning period (day 36), and the period of
sexual maturity and adult life (days 84, 160 and
365). In the early postnatal period (<36 days), profound changes
occur in substrate metabolism in the heart and muscle, whereas
thereafter (>36 days), changes continue to occur in muscle
architecture and capillarization (31, 32). We have
presented new data that indicate that postnatal MCT protein expression
is regulated in an isoform- and tissue-specific manner. Specifically,
1) over a 1-yr period, MCT1 protein content was not altered
in the heart, whereas 2) MCT1 was increased in soleus muscle
to adult levels by 36-84 days of age. In contrast, 3)
in the heart, MCT4 protein expression was completely repressed within
the first 36 days of life, and 4) MCT4 protein expression in
soleus muscle was rapidly repressed (60%) in the first 84 days of
life and was almost fully repressed (
90%) by 1 yr of age.
For comparison purposes, we also measured the changes in GLUT-4 protein and mRNA in heart and muscle. In agreement with other studies (30, 34, 36), we also observed that GLUT-4 protein and mRNA were increased in soleus muscle and in the heart (Fig. 7). Thus the data obtained on GLUT-4 protein and GLUT-4 mRNA provided a positive control for our studies.
In the present studies, MCT1 was not altered in the heart but was increased in soleus muscle, whereas MCT4 was reduced in both tissues. Tissue- and isoform-specific changes have previously been observed in the glucose transporter proteins GLUT-1 and GLUT-4. From birth until 16 days of age, GLUT-1 is repressed ~50-fold, whereas GLUT-4 is increased about sixfold during this same period in heart and muscle (30). Others have shown similar increases in heart and muscle GLUT-4 during postnatal development (days 0-41), whereas adipose tissue GLUT-4 is concomitantly decreased (34). Thus the tissue- and isoform-specific changes in MCT1 and MCT4 are consistent with observations made previously for GLUT-1 and GLUT-4 transport proteins.
The mechanisms for these tissue- and isoform-specific changes in MCT1 and MCT4 over the course of 1 yr are difficult to identify. It is known that GLUT-4 expression in perinatal life is regulated by thyroid hormone in the heart but not in brown adipose tissue (9), but whether this hormone also regulates MCT1 and MCT4 is not known. It has also been suggested that the dietary changes in the suckling-to-weaning transition period may account for differences in tissue-specific expression of GLUT-4 during development (see Ref. 34 for discussion). However, this is speculative, and to date, the regulation of MCT transporter expression by diet has not been examined.
In the heart, no changes were observed in PFK or CS activity, whereas
the activities of both of these enzymes were altered in the soleus
muscles from the same animals (i.e., CS was increased, whereas PFK was
decreased). The lack of changes in these enzymes in the heart seems to
be at odds with the known reductions in glycolysis and the concomitant
increase in fatty acid oxidation in the heart (13, 22).
For example, in rabbit hearts, from days 1 to 7 of life, rates of glycolysis and glucose oxidation were decreased 80 and 50%, respectively, whereas palmitate and lactate oxidation rates
were increased 1,200 and 170%, respectively (22). Fatty
acid metabolism in the rat heart is also increased during development
and attains adult oxidation rates 20 days after birth
(13). Thus it may be that measuring the maximal activities of PFK and CS does not provide a good index of changes in substrate metabolism in the heart. Perhaps other markers (e.g.,
-hydroxyacyl-CoA dehydrogenase or fatty acid transporters)
would have provided a better index of the changes in substrate
metabolism in the heart.
Despite the lack of changes in PFK and CS activities in the heart, the reduction in glycolysis, along with a concomitant increase in fatty acid oxidation in the developing heart (13, 22), would seem to provide a partial explanation for the reduction in MCT4 in this tissue, because we (4, 38) and others (11) have previously suggested that the MCT4 isoform may have a specialized role to facilitate the extrusion of lactate from the tissue. Thus, as the heart becomes more reliant on fatty acid metabolism and glycolysis is reduced (13, 22), the need for lactate extrusion is also reduced. Consequently, the need for MCT4, a low-affinity lactate transporter (Km ~30 mM) (11) that exports lactate out of the tissue (4, 11, 38), is also reduced.
MCT1 levels were not altered in the heart despite the changes in fuel metabolism that occur in the early postnatal period. We did not observe any changes in the activity of the mitochondrial marker enzyme CS over the course of 1 yr. The recent reports that MCT1 in heart is present in the plasma membrane (18) and mitochondria (7) support our suggestions (2, 5, 24, 25, 38) that the MCT1 transporter is located to favor the uptake of lactate and to facilitate the oxidative disposal of lactate. The lack of change in MCT1 suggests that the lactate uptake and oxidation capacities in the rat heart are not altered during the first year of life (days 10-365). However, in the rabbit heart, lactate oxidation is increased (+170%) in the 1st wk of life (22). Our first measurements in rat hearts were obtained at 10 days of age. There is some kinetic evidence to suggest that rat hearts express another MCT protein (37), which has not yet been cloned. It may well be that this MCT is more closely linked to changes in the substrate metabolism in the neonatal heart.
In contrast to the heart MCT1, soleus muscle MCT1 was increased during the early postnatal period (<36 days). This increase in MCT1 parallels the increase in oxidative metabolism in the soleus muscle during the same time period (32). This is likely due to the increased postural work being performed by the soleus muscle in the rapidly growing neonate (12). In the first few weeks of life (days 10-36) there was a 40% increase in CS activity, which is similar to the increase in succinate dehydrogenase activity observed in the 7- to 30-day postnatal period in rat soleus muscle (32). Previously, we have shown, in adult muscle, that MCT1 expression is closely correlated with the muscles' oxidative capacities (24, 25); therefore, we (24, 25) have proposed that MCT1 expression may reflect the ability of muscle to oxidize lactate. Recently, MCT1 has been localized to the plasma membrane (4) and mitochondrion in skeletal muscle (7). This subcellular distribution of MCT1 would favor the uptake and oxidative disposal of lactate. When we (5) increased the oxidative capacity of muscle via chronic electrical stimulation, MCT1, but not MCT4, was increased, and at the same time, lactate uptake was also increased. In addition, in similar studies, we found that lactate uptake in control and experimental muscles was highly correlated with the MCT1 content of these muscles (r = 0.93) (24). Thus our studies (5, 24) indicated that an increase in MCT1 alone is sufficient to increase lactate uptake by muscle. Consequently, we can surmise that the increase in soleus muscle MCT1 in the present study enhanced the capacity for lactate uptake by this muscle.
The decrement in soleus muscle MCT4 is likely attributable to the reduction in fast-twitch muscle fibers in the soleus muscle (12, 32), because MCT4 is expressed primarily in these fast-twitch muscle fibers (4, 38). Along with the reduction in fast-twitch fibers is a reduced capacity for glycolytic metabolism in this muscle. We (4, 38) have previously suggested that the MCT4 isoform may have a specialized role in muscle, namely, to facilitate the extrusion of lactate from the tissue. This suggestion is given further credence in the present study, because the greatest reduction in MCT4 protein roughly parallels the reduced glycolytic capacity of the soleus muscle, as indicated by the reduction in PFK activity. Given that MCT4 is confined to the fast-twitch muscle fibers (4, 38), the MCT4 in the 1-yr-old soleus muscle is presumably attributable to the few remaining fast-twitch oxidative fibers (1, 25).
There is good reason to believe that skeletal muscle activity is one factor regulating the expression of MCT1 and MCT4, although the type of muscle activity may be critical. When muscles are denervated, both MCT1 and MCT4 are decreased (38). However, when muscle activity is increased and the oxidative capacity of the muscles is enhanced, then MCT1 is also increased [i.e., 1) with increased postural work by soleus (present study), 2) with treadmill training (2), or 3) with increased contractile activity induced with chronic electrical stimulation (24)]. However, these types of aerobic muscle activity patterns can either reduce MCT4 in young animals (present study) or fail to alter MCT4 in mature animals [i.e., chronic muscle stimulation (5)]. With more intense contractile activity, both MCT1 (+70%) and MCT4 (+30%) have been shown to be increased (26). Thus the intensity of muscle contractile activity may be a critical determinant regulating the expression of MCT1 and MCT4.
The changes in the relative levels of MCT1 mRNA in heart and soleus muscle over the course of 1 yr paralleled the pattern observed for the MCT1 protein. This suggests that MCT1 gene expression is regulated at the transcriptional and/or posttranscriptional level. Similar processes may regulate MCT4 gene expression in heart, because both MCT4 mRNA and MCT4 protein were rapidly reduced in the heart (<36 days). More complex regulation of MCT4 gene expression may occur in the soleus muscle, because MCT4 mRNA levels were elevated at the same time that MCT4 protein was decreased. This suggests that MCT4 gene expression in the soleus muscle may be controlled at the posttranscriptional and/or translational level. It is possible that MCT4 mRNA may be masked and unavailable for translation, as found for the developmental expression of the small subunit of ribonucleotide reductase, cyclin A, and fibroblast growth factor receptor-1 (28, 33, 35). Alternatively, MCT4 mRNA may bind an inhibitory protein that prevents translation, as has been shown for the regulation of ferritin gene expression (21). At present, we have no data that can provide an explanation for the regulation of MCT4. Interestingly, in previous studies, we found that the relative levels of MCT1 protein and mRNA are correlated in different muscle types, whereas MCT4 protein and mRNA are not correlated (4). Elucidation of the mechanisms regulating MCT4 gene expression will require additional experiments.
In summary, we have shown that MCT protein expression over the course of 1 yr, in soleus muscle and the heart, is regulated in 1) an isoform-specific manner and 2) a tissue-specific manner. It appears, therefore, that in both the heart and soleus muscle, MCT4 expression is repressed at the same time that glycolysis is reduced in these tissues. Thus, in muscle and heart, MCT4 expression conforms to our suggestions that this MCT isoform may have a specialized role to facilitate the extrusion of lactate from the tissue (4, 38). Conversely, the increase in MCT1 in the soleus muscle parallels the increase in slow-twitch oxidative muscle fibers in this muscle in the first few months of life (12, 32). This is consistent with our suggestions (4, 24, 25, 38) that MCT1 expression may reflect the ability of muscle to oxidize lactate. In contrast to soleus muscle, in the heart, MCT1 expression is not coordinated with known changes in substrate metabolism. There may be an as-yet-undiscovered MCT in the heart that is more closely regulated with changes in cardiac substrate metabolism. Although the mechanisms regulating MCT1 and MCT4 expression are not known, the present study suggests that MCT1 expression in the heart and MCT1 and MCT4 expression in the soleus are regulated by pretranslational processes, whereas posttranscriptional processes regulate MCT4 expression in the soleus muscle.
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ACKNOWLEDGEMENTS |
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We thank Dr. A. P. Halestrap, Dept. of Biochemistry, University of Bristol, Bristol, UK, for providing the MCT1 and MCT4 antibody and the MCT1 cDNA and MCT4 cDNA for our studies.
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FOOTNOTES |
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These studies were supported by the Heart and Stroke Foundation of Ontario and by the Natural Sciences and Engineering Research Council of Canada.
Address for reprint requests and other correspondence: A. Bonen, Dept. of Kinesiology, Univ. of Waterloo, Waterloo, ON N2L 3G1, Canada (E-mail: abonen{at}healthy.uwaterloo.ca).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 10 October 2000; accepted in final form 3 May 2001.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Armstrong, RB,
and
Phelps RO.
Muscle fiber type composition of the rat hindlimb.
Am J Anat
171:
259-272,
1984[ISI][Medline].
2.
Baker, SK,
McCullagh KJA,
and
Bonen A.
Training intensity- dependent and tissue-specific increases in lactate uptake and MCT-1 in heart and muscle.
J Appl Physiol
84:
987-994,
1998
3.
Barnard, RJ,
Lawani LO,
Martin DA,
Youngren JF,
Singh R,
and
Scheck SH.
Effects of maturation and aging on the skeletal muscle glucose transport system.
Am J Physiol Endocrinol Metab
262:
E619-E626,
1992
4.
Bonen, A,
Miskovic D,
Tonouchi M,
Lemieux K,
Wilson MC,
Marette A,
and
Halestrap AP.
Abundance and subcellular distribution of MCT1 and MCT4 in heart and fast-twitch skeletal muscles.
Am J Physiol Endocrinol Metab
278:
E1067-E1077,
2000
5.
Bonen, A,
Tonuchi M,
Miskovic D,
Heddle C,
Heikkila JJ,
and
Halestrap AP.
Isoform-specific regulation of the lactate transporters MCT1 and MCT4 by contractile activity.
Am J Physiol Endocrinol Metab
279:
E1131-E1138,
2000
6.
Broer, S,
Schneider HP,
Broer A,
Rahman B,
Hamprecht B,
and
Deitmer JW.
Characterization of the monocarboxylate transporter 1 expressed in Xenopus laevis oocytes by changes in cytosolic pH.
Biochem J
333:
167-174,
1998[ISI][Medline].
7.
Brooks, GA,
Brown MA,
Butz CE,
Sicurello JP,
and
Dubouchaud H.
Cardiac and skeletal muscle mitochondria have a monocarboxylate transporter MCT1.
J Appl Physiol
87:
1713-1718,
1999
8.
Cartee, GD,
Briggs-Tung C,
and
Kietzke EW.
Persistent effects of exercise on skeletal muscle glucose transport across the life-span of rats.
J Appl Physiol
75:
972-978,
1993[Abstract].
9.
Castello, A,
Cadefau J,
Cusso R,
Testar X,
Hesketh JE,
Palacin M,
and
Zorzano A.
GLUT4 and GLUT1 glucose transporter expression is differentially regulated by contractile activity in skeletal muscle.
J Biol Chem
268:
14998-15003,
1993
10.
Castello, A,
Rodriguez-Manzaneque JC,
Camps M,
Perez-Castillo A,
Testar X,
Palacin M,
Santos A,
and
Zorzano A.
Perinatal hypothyroidism impairs the normal transition of GLUT4 and GLUT1 glucose transporters from fetal to neonatal levels in heart and brown adipose tissue. Evidence for the tissue specific regulation of GLUT4 expression by thyroid hormone.
J Biol Chem
296:
5905-5912,
1994.
11.
Dimmer, KS,
Friedrich B,
Lang F,
Deitmer JW,
and
Broer S.
The low affinity monocarboxylate transporter MCT4 is adapted to the export of lactate in highly glycolytic cells.
Biochem J
350:
219-227,
2000[ISI][Medline].
12.
Elder, GCB,
and
McComas AJ.
Development of rat muscle short- and long-term hindlimb suspension.
J Appl Physiol
62:
1917-1923,
1987
13.
Glatz, JFC,
and
Veerkamp JH.
Postnatal development of palmitate oxidation and mitochondrial enzyme activities in rat cardiac and skeletal muscles.
Biochim Biophys Acta
711:
327-335,
1982[ISI][Medline].
14.
Goodman, MN,
Dluz SM,
McElaney MA,
Belur E,
and
Ruderman NB.
Glucose uptake and insulin sensitivity in rat muscle: changes during 3-96 weeks of age.
Am J Physiol Endocrinol Metab
244:
E93-E100,
1983
15.
Gulve, EA,
Henriksen EJ,
Rodnick KJ,
Youn JH,
and
Holloszy JO.
Glucose transporters and glucose transport in skeletal muscles of 1- to 25-mo-old rats.
Am J Physiol Endocrinol Metab
264:
E319-E327,
1993
16.
Halestrap, AP,
and
Price NT.
The proton-linked monocarboxylate transporter family: structure, function and regulation.
Biochem J
343:
281-299,
1999[ISI][Medline].
17.
Jackson, VN,
Price NT,
and
Halestrap AP.
cDNA cloning of MCT1, a monocarboxylate transporter from rat skeletal muscle.
Biochim Biophys Acta
1238:
193-196,
1995[ISI][Medline].
18.
Johannsson, E,
Nagelhus EA,
McCullagh KJA,
Sejersted OM,
Blackstad TW,
Bonen A,
and
Ottersen OP.
Cellular and subcellular expression of the monocarboxylate transporter MCT1 in rat heart. A high resolution immunogold analysis.
Circ Res
80:
400-407,
1997[ISI][Medline].
19.
Juel, C.
Lactate-proton cotransport in skeletal muscle.
Physiol Rev
77:
321-358,
1997
20.
Kern, M,
Dolan PL,
Mazzeo RS,
Wells JA,
and
Dohm GL.
Effect of aging and exercise on GLUT-4 glucose transporters in muscle.
Am J Physiol Endocrinol Metab
263:
E362-E367,
1992
21.
Klausner, RD,
Rouault TA,
and
Harford JB.
Regulating the fate of mRNA: the control of cellular iron metabolism.
Cell
72:
19-28,
1993[ISI][Medline].
22.
Lopaschuk, GD,
Spafford MA,
and
Marsh DR.
Glycolysis is predominant source of myocardial ATP production immediately after birth.
Am J Physiol Heart Circ Physiol
261:
H1698-H1705,
1991
23.
Lowry, OH,
and
Passonneau JV.
A Flexible System of Enzymatic Analysis. New York: Academic, 1972.
24.
McCullagh, KJA,
Poole RC,
Halestrap AP,
O'Brien M,
and
Bonen A.
Chronic electrical stimulation increases MCT1 and lactate uptake in red and white skeletal muscle.
Am J Physiol Endocrinol Metab
273:
E239-E246,
1997
25.
McCullagh, KJA,
Poole RC,
Halestrap AP,
O'Brien M,
and
Bonen A.
Role of the lactate transporter (MCT1) in skeletal muscles.
Am J Physiol Endocrinol Metab
271:
E143-E150,
1996
26.
Pilegaard, H,
Domino K,
Noland T,
Juel C,
Hellsten Y,
Halestrap AP,
and
Bangsbo J.
Effect of high-intensity exercise training on lactate/H+ transport capacity in human skeletal muscle.
Am J Physiol Endocrinol Metab
276:
E255-E261,
1999
27.
Price, NT,
Jackson VN,
and
Halestrap AP.
Cloning and sequencing of four new mammalian monocarboxylate transporter (MCT) homologues confirms the existence of a transporter family with an ancient past.
Biochem J
329:
321-328,
1998[ISI][Medline].
28.
Robbie, EP,
Peterson M,
Amaya E,
and
Musci TJ.
Temporal regulation of the Xenopus FGF receptor in development: a translation inhibiting element in the 3' untranslated region.
Development
121:
1775-1785,
1995
29.
Sambrook, J,
Fritisch EF,
and
Maniatis T.
Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, NY: Cold Spring Harbor, 1989.
30.
Santalucia, PS,
Camps M,
Castello A,
Munoz P,
Nuel A,
Testar X,
Palacin M,
and
Zorzano A.
Developmental regulation of GLUT-1 (erythroid/Hep G2) and GLUT4 (muscle/fat) glucose transporter expression in rat heart, skeletal muscle, and brown adipose tissue.
Endocrinology
130:
837-846,
1992[Abstract].
31.
Smith, D,
Green H,
Thomson J,
and
Sharratt M.
Capillary and size interrelationships in the developing rat diaphragm, EDL, and soleus muscle fiber types.
Am J Physiol Cell Physiol
256:
C50-C58,
1989
32.
Smith, D,
Green H,
Thomson J,
and
Sharratt M.
Oxidative potential in developing rat diaphragm, EDL, and soleus muscle fibers.
Am J Physiol Cell Physiol
254:
C661-C668,
1988
33.
Standart, N.
Masking and unmasking of maternal mRNAs.
Semin Dev Biol
3:
367-379,
1992.
34.
Studelska, DR,
Campbell C,
Pang S,
Rodnick KJ,
and
James DE.
Developmental expression of the insulin-regulatable glucose transporter GLUT-4.
Am J Physiol Endocrinol Metab
263:
E102-E106,
1992
35.
Walker, J,
Dale M,
and
Standart N.
Unmasking messenger RNA in clam oocytes: role of phosphorylation of a 3' UTR masking element-binding protein at fertilization.
Dev Biol
173:
292-305,
1996[ISI][Medline].
36.
Wang, C,
and
Hu SM.
Developmental regulation in the expression of heart glucose transporters.
Biochem Biophys Res Commun
177:
1095-1100,
1991[ISI][Medline].
37.
Wang, X,
Levi AJ,
and
Halestrap AP.
Substrate and inhibitor specificity of monocarboxylate transporters of single rat heart cells.
Am J Physiol Heart Circ Physiol
270:
H476-H484,
1996
38.
Wilson, MC,
Jackson VN,
Hedle C,
Price NT,
Pilegaard H,
Juel C,
Bonen A,
Montgomery I,
Hutter OF,
and
Halestrap AP.
Lactic acid efflux from white skeletal muscle is catalyzed by the monocarboxylate transporter MCT3.
J Biol Chem
273:
15920-15926,
1998