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Department of Physiology and Cell Biology, Albany Medical College, Albany, New York 12208
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ABSTRACT |
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Top
Abstract
Introduction
Procedures
Results
Discussion
References
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Basal and insulin-stimulated activity of Akt1 kinase and uptake of 2-deoxy-D-glucose (2-DG) were measured in soleus (slow-twitch) and plantaris (fast-twitch) muscles of rats at 1 and 3 days after sectioning the sciatic nerve in one hindlimb of the animals. At 1 day after surgery, the insulin-stimulated activity of Akt1 kinase in denervated soleus and plantaris muscles remained unchanged, but the insulin-stimulated 2-DG uptake by these muscles was reduced by 71 and 61%, respectively, compared with the corresponding muscles of the contralateral sham (control) hindlimb. At 3 days, the insulin-stimulated activity of Akt1 kinase in the denervated soleus and plantaris muscles was 86 and 71% lower, respectively, than in their sham counterparts. At this time point, the denervated soleus muscles showed no increase in 2-DG uptake in response to insulin. In contrast, the denervated plantaris muscle exhibited the same absolute level of insulin-stimulated 2-DG uptake as the sham plantaris muscle; however, the insulin-induced increment in 2-DG uptake was reduced by 60%, whereas basal 2-DG uptake was increased by 251% compared with the sham plantaris muscle. None of the denervated muscles showed a decrease in the abundance of Akt1 kinase. The results demonstrate that the causes of insulin resistance in denervated muscles are dependent on time after surgery. Initially, they involve only mechanisms downstream of Akt1 kinase (day 1), whereas at day 3 they also involve mechanisms upstream of, and including, Akt1 kinase.
protein kinase B
; 2-deoxyglucose uptake; soleus muscle; plantaris muscle; slow-twitch and fast-twitch muscles
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INTRODUCTION |
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Top
Abstract
Introduction
Procedures
Results
Discussion
References
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STIMULATION OF GLUCOSE uptake by insulin is initiated
by insulin binding to its disulfide-linked heterotetrameric receptor consisting of two extracellular -subunits and two transmembrane 
-subunits. Insulin binding to the -subunit rapidly results in receptor autophosphorylation and activation of an intrinsic tyrosine kinase associated with the -subunit (7). The receptor tyrosine kinase phosphorylates insulin receptor substrates (IRS), which enables
the regulatory subunit (p85) of phosphatidylinositol 3-kinase to bind
to IRS. The binding of p85 to IRS then results in the activation of the
catalytic subunit (p110) of phosphatidylinositol 3-kinase (7). The
product of the phosphatidylinositol 3-kinase reaction,
phosphatidylinositol 3,4,5-trisphosphate, may serve as a link to the
activation of 3-phosphoinositide-dependent protein kinase-1 (9), which
in turn phosphorylates Akt1 kinase, also referred to as protein kinase
B or RAC kinase, at Thr-308 (2). The role of Akt1 kinase in mediating
the insulin-induced stimulation of glucose uptake is suggested by the
observation that transfection of a constitutively active Akt1 kinase
into 3T3-L1 adipocytes has an insulin-like effect on the translocation
of GLUT-4 transporter to the plasma membrane and glucose uptake (13).
The regulation of Akt1 kinase activity is incompletely understood. The
full activation of Akt1 kinase requires phosphorylation of both Thr-308
and Ser-473 (1). Because phosphoinositide-dependent protein kinase-1
phosphorylates Akt1 kinase only on Thr-308 (2), an additional, so far
unknown, serine kinase is believed to participate in the regulation of Akt1 kinase activity.
A single hindlimb denervation in the rat is a useful and highly reproducible model of insulin resistance. In this model, muscles of the denervated hindlimb develop insulin resistance, whereas muscles of the contralateral sham hindlimb respond to insulin in a normal fashion and serve as an internal control (16). Interruption of nerve supply to skeletal muscle results in the development of insulin resistance characterized by a decreased ability or inability of insulin to stimulate the transport of sugars (4, 6, 16), glycogen synthesis (4), or amino acid transport (16) in the affected muscles. The signs of insulin resistance in the denervated rat muscles in vivo can be observed as early as 3 h after sectioning the nerve (the earliest time tested) (16). We have previously demonstrated that both slow-twitch and fast-twitch muscles exhibit a progressive lowering of insulin-induced glucose uptake in vivo during the first 24 h after sectioning the sciatic nerve but that the two kinds of muscles differ in the manifestations of insulin resistance at 3-17 days after denervation (16). During the latter period, the slow-twitch muscles become completely unresponsive to stimulation with insulin, whereas the fast-twitch muscles show a normal glucose uptake when stimulated by insulin. However, the insulin-induced increment in glucose uptake is reduced because it is superimposed on already elevated basal glucose uptake.
The present study was undertaken to investigate how closely the insulin-stimulated activity of Akt1 kinase parallels the insulin-stimulated glucose uptake in hindlimb muscles of rats after a single hindlimb denervation. This study extends observations on insulin receptor tyrosine kinase and phosphatidylinositol 3-kinase activities in denervated soleus and plantaris muscles reported recently (11).
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EXPERIMENTAL PROCEDURES |
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Top
Abstract
Introduction
Procedures
Results
Discussion
References
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Materials.
Anti-human Akt1/PKB plekstrin homology domain sheep polyclonal
antibody, horseradish peroxidase (HRP)-conjugated rabbit anti-sheep antibody, cAMP-dependent protein kinase inhibitor peptide, and Akt/PKB
specific substrate peptide were purchased from Upstate Biotechnology
(Lake Placid, NY). Protein G-Sepharose (GammaBind G-Sepharose) was from
Pharmacia (Piscataway, NJ).
[
-32P]ATP and
2-deoxy-D-[1,2-3H(N)]glucose
were from New England Nuclear (Boston, MA).
[U-14C]sucrose was
obtained from ICN Pharmaceuticals (Costa Mesa, CA). Microcystin was
from Calbiochem (San Diego, CA). Leupeptin, pepstatin, as well as other
chemicals were from Sigma (St. Louis, MO).
Animals. The experiments were performed on adult male Sprague-Dawley rats weighing 225-240 g. All experimental procedures were approved by the Institutional Animal Care and Use Committee and the institutional veterinarian and strictly adhered to the National Institutes of Health Guide for the Care and Use of Laboratory Animals [Department of Health and Human Services Publication No. (NIH) 85-23, Revised 1985]. The right hindlimb of each rat was denervated under ether anesthesia, as previously described (11, 16-19). Briefly, the thigh muscles were bluntly separated from the lateral side, and a 5-mm segment of the sciatic nerve was excised. On the contralateral (sham) hindlimb, the sciatic nerve was visualized in the same way, but not touched. The skin wounds were closed with surgical clips and coated with disinfectant (Betadine). No bleeding was associated with the surgery, and no infection was observed during the subsequent recovery period. The denervation had no effect on daily food intake during the experimental period. The rats were studied at 1 and 3 days after surgery. At these test times, muscles from the denervated hindlimb display minimal, if any, changes in muscle mass or extracellular fluid volume (16). All animals were fasted overnight (18 h) before the experiment and were anesthetized with 50 mg/kg body wt pentobarbital sodium given intraperitoneally at the time of the experiment.
Cellular uptake of 2-deoxy-D-glucose. Glucose uptake by individual hindlimb muscles in vivo was assessed by cellular accumulation of labeled 2-deoxy-D-glucose as described previously (11, 16, 17). Pentobarbital sodium-anesthetized animals were injected with 10 µCi 2-deoxy-D-[1,2-3H(N)]glucose and 2 µCi [U-14C]sucrose with or without 0.1 U bovine insulin in 0.4 ml of 0.1% defatted bovine serum albumin/rat via the dorsal vein of the penis. The animals were killed by rapid exsanguination 25 min after the injection of labeled substances. Blood was collected, and soleus and plantaris muscles were excised from both hindlimbs. The muscles and serum were digested separately in tissue solubilizer (Solvable, New England Nuclear), and the 3H and 14C radioactivities were determined by liquid scintillation counting. Cellular uptake of 2-deoxy-D-glucose was calculated as the difference between the total tissue 3H radioactivity (in dpm) and the amount of 3H radioactivity present in the tissue extracellular ([14C]sucrose) space.
Activity and abundance of Akt1 kinase.
Pentobarbital sodium-anesthetized animals were injected with 0.4 ml of
0.1% bovine serum albumin with 0 or 0.1 U bovine insulin/rat via the
dorsal vein of the penis. A preliminary study indicated that the
insulin-stimulated activity of Akt1 kinase peaked in both soleus and
plantaris muscles at 5 min and remained above control level for at
least 15 min (data not shown). This time course is in agreement with
studies by Cross et al. (10). Therefore, soleus and plantaris muscles
were quickly excised at 5 min after the intravenous injection. In each
rat, the muscles were excised only from one hindlimb, either the
denervated hindlimb or the contralateral sham hindlimb, to ensure that
the muscles were removed exactly at the 5-min interval. Each excised
muscle was immediately frozen in liquid nitrogen and subsequently kept
at 
85°C until further use. Each muscle was powdered under
liquid nitrogen within 24 h. The powder was transferred into a 6-ml
polypropylene tube containing 0.5 ml of ice-cold
buffer A/100 mg muscle. The
composition of buffer A was 50 mM
Tris, pH 7.5, 1 mM EDTA, 1 mM EGTA, 0.5 mM
Na3VO4,
0.1% 2-mercaptoethanol, 1% Triton X-100, 50 mM NaF, 5 mM sodium
pyrophosphate, 10 mM sodium -glycerol phosphate, 0.1 mM
phenylmethylsulfonyl fluoride, 1 µg/ml aprotinin, 1 µg/ml pepstatin, 1 µg/ml leupeptin, and 1 µM microcystin. The suspension was homogenized using three 10-s bursts of a Polytron homogenizer set
at 75% of maximum power. The test tube with the homogenate was kept in
an ice bath during the homogenization. After centrifugation at 13,000 g and 4°C for 15 min, the
supernatant of muscle homogenate was separated, frozen in liquid
nitrogen, and kept at 85°C until further use.
pleckstrin homology domain sheep polyclonal
antibody overnight at 4°C. The antibody-protein G-Sepharose complex
was washed three times with buffer A
and then allowed to react with 500 µg muscle homogenate supernatant
protein (Bradford protein assay) under constant agitation at 4°C
for 90 min. The enzyme-antibody-protein G-Sepharose complex was washed
three times with buffer A containing
0.5 M NaCl, two times with buffer B
[50 mM Tris · HCl, pH 7.5, 0.03% (wt/vol) Brij-35, 0.1 mM EGTA, and 0.1% 2-mercaptoethanol], and twice
with assay dilution buffer (20 mM MOPS, pH 7.2, 25 mM -glycerol
phosphate, 5 mM EGTA, 1 mM sodium orthovanadate, and 1 mM
dithiothreitol). The enzyme-antibody-protein G-Sepharose
complex was subsequently incubated with 40 µl of assay dilution
buffer containing 10 µM cAMP-dependent protein kinase inhibitor
peptide, 100 µM Akt/PKB specific substrate peptide, 125 µM ATP
(with 10 µCi
[-32P]ATP per
reaction mixture), and 19 mM MgCl2
for 10 min at 30°C with continuous shaking. The 40-µl supernatant
was then transferred into another tube, mixed with 20 µl of 40% TCA,
and incubated at room temperature for 5 min. After mixing, 40 µl of
TCA mixture were applied onto a 2 cm × 2 cm P81 phosphocellulose
paper and allowed to bind to it for 30 s before immersing the square in 0.75% phosphoric acid. The collected phosphocellulose squares were
washed three times with 0.75% phosphoric acid and once with acetone
for 5 min per wash under continuous mixing. The radioactivity of each
square was determined by scintillation counting. Radioactivity of
samples that did not contain Akt1 kinase (enzyme blank) was subtracted
from measured radioactivities.
To determine the abundance of Akt1 kinase, aliquots of supernatants of
muscle homogenates were prepared for SDS-PAGE by diluting them in
electrophoresis-reducing sample buffer and heating them at 98°C for
4 min. Aliquots corresponding to 10 µg protein were subjected to
SDS-PAGE using 4% stacking gels and 8% resolving gels and transferred
electrophoretically to pure nitrocellulose membranes (Bio-Rad,
Hercules, CA). The membranes were washed twice with water and blocked
under constant agitation in freshly prepared Tris-buffered saline, pH
7.4, containing 0.05% Tween 20 and 3% nonfat dry milk (TBS-T-MILK) at
21°C for 30 min. The membranes were then agitated overnight at
4°C in TBS-T-MILK containing 0.75 µg/ml anti-human Akt1/PKB
pleckstrin homology domain sheep IgG. After being washed twice with
water, the membranes were agitated at 21°C for 90 min in PBS, pH
7.4, with 3% nonfat dry milk containing a rabbit anti-sheep
HRP-conjugated IgG at a dilution of 1:1,500. The nitrocellulose
membranes were subsequently washed in water (twice) then in PBS-0.05%
Tween 20 for 3-5 min, and finally in four or five changes of
water. Blots were detected by enhanced chemiluminescence (Amersham,
Arlington Heights, IL). Bands corresponding to Akt1 kinase were
quantified by video densitometry (Bioimage 60S; Millipore, Bedford,
MA).
Data evaluation. The results are expressed as means ± SE. Statistical significance was assessed using ANOVA followed by the Student-Newman-Keuls multiple-comparison test.
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RESULTS |
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Top
Abstract
Introduction
Procedures
Results
Discussion
References
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Soleus muscle 1 day after denervation. In agreement with previous studies (11, 16), the denervated soleus muscle exhibited a 49% (P < 0.005) lower basal 2-deoxy-D-glucose uptake and a 71% (P < 0.002) lower insulin-stimulated 2-deoxy-D-glucose uptake in vivo compared with the contralateral sham soleus muscle (Fig. 1A). Our previous studies have shown that these changes occur in the absence of any alteration in insulin binding, basal and insulin-stimulated tyrosine kinase activity of the insulin receptor, basal and insulin-stimulated activity of phosphatidylinositol 3-kinase, and the abundance of GLUT-1 and GLUT-4 in the denervated soleus muscle (11). The present study extends these observations by assessing the activity of Akt1 kinase (Fig. 1B). Basal activity of Akt1 kinase in muscles was very low and was not statistically different from background phosphorylation (enzyme blank). Administration of insulin resulted in pronounced increases in the activities of Akt1 kinase in both sham and denervated soleus muscles, and there was no difference in the magnitude of the insulin-stimulated Akt1 kinase activity between the sham and denervated soleus muscles. Despite this similarity, the denervated soleus muscle exhibited a 29% (P < 0.04) greater abundance of Akt1 kinase than the contralateral sham soleus muscle (Fig. 1C).
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Plantaris muscle 1 day after denervation. Basal 2-deoxy-D-glucose uptake by the sham plantaris muscle did not differ from that in sham soleus muscle, but the insulin-induced uptake by the sham plantaris muscle was 50% (P < 0.02) lower than that in the sham soleus muscle (Fig. 1A). The denervated plantaris muscle exhibited no change in basal 2-deoxy-D-glucose uptake, but its insulin-stimulated uptake was reduced by 61% (P < 0.001) compared with the contralateral sham plantaris muscle (Fig. 1A). Our previous studies have demonstrated that the insulin resistance of the denervated plantaris muscle at this time point is associated with unchanged insulin binding, unchanged basal and insulin-stimulated activities of tyrosine kinase of the insulin receptor and of phosphatidylinositol 3-kinase, and unchanged abundance of GLUT-1 and GLUT-4 (11). Figure 1, B and C, also shows that the insulin resistance of the denervated plantaris muscle occurs in the absence of any alteration in the insulin-induced activity of Akt1 kinase or its abundance in the denervated plantaris muscle.
Aside from the absence of effects of denervation, it is noteworthy that insulin-stimulated activities of Akt1 kinase in sham and denervated plantaris muscles were 39 and 44% (P < 0.05) lower, respectively, than those of sham and denervated soleus muscles (Fig. 1B). Also, the abundance of Akt1 kinase in sham and denervated plantaris muscles was 43 and 58% (P < 0.006) lower, respectively, than those of sham and denervated soleus muscles (Fig. 1C).Soleus muscle 3 days after denervation. At this time point, the denervated soleus muscle exhibited a 60% (P < 0.03) lower basal 2-deoxy-D-glucose uptake than the contralateral sham soleus muscle and was completely unresponsive to stimulation with insulin (Fig. 2A). Our previous findings have shown that insulin binding was not significantly altered at this interval, but the denervated soleus muscle exhibited a 35% decrease in insulin-induced tyrosine kinase activity of the insulin receptor, a 63% decrease in insulin-stimulated activity of phosphatidylinositol 3-kinase, and a pronounced decrease in the tissue abundance of GLUT-4 transporter compared with the contralateral sham soleus muscle (11). As depicted in Fig. 2, B and C, the denervated soleus muscle also shows an 86% (P < 0.001) decrease in insulin-stimulated Akt1 kinase activity compared with the contralateral sham counterpart, whereas the abundance of Akt1 kinase in the denervated soleus muscle appears to be, in fact, increased 43% (P = 0.06) compared with the sham soleus muscle.
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Plantaris muscle 3 days after denervation. In agreement with studies on rats 1 day after a single hindlimb denervation, sham plantaris muscle from 3-day postsurgery rats (Fig. 2A) showed a 38% lower basal 2-deoxy-D-glucose uptake and a 44% lower insulin-stimulated uptake compared with the adjacent sham soleus muscle (P < 0.05).
The denervated plantaris muscle exhibited a 251% (P < 0.001) elevation in basal 2-deoxy-D-glucose uptake and an unchanged absolute level of insulin-induced 2-deoxy-D-glucose uptake compared with the contralateral sham plantaris muscle. It should be noted, however, that the insulin-induced increment in uptake in the denervated plantaris muscle, although statistically significant (P < 0.03), was reduced by 60% (P < 0.007) compared with the contralateral sham plantaris muscle. Although insulin binding is not altered in the plantaris muscle 3 days after denervation (11), we have previously observed a 44% lower insulin-stimulated tyrosine kinase activity of the insulin receptor, a 41% lower insulin-stimulated activity of phosphatidylinositol 3-kinase, diminished abundance of GLUT-4, and increased abundance of GLUT-1 in the denervated plantaris muscle compared with its sham counterpart (11). As shown in Fig. 2B, the insulin-stimulated activity of Akt1 kinase in the denervated plantaris muscle is 71% (P < 0.002) lower than that in the contralateral sham plantaris muscle. The abundance of Akt1 kinase in the denervated plantaris muscle appeared to be 63% higher than in its sham counterpart, but the difference was not statistically significant (Fig. 2C). It should be noted that sham muscles of rats 3 days after a single hindlimb denervation (Fig. 2, B and C) exhibited the same difference in insulin-stimulated activity and abundance of Akt1 kinase as slow-twitch and fast-twitch muscles of rats studied 1 day after surgery (Fig. 1, B and C). As shown in Fig. 2, B and C, the insulin-stimulated activity of Akt1 kinase and the abundance of this enzyme in the sham plantaris muscle were 50% (P < 0.001) and 60% (P < 0.04) lower, respectively, than those in the sham soleus muscle.| |
DISCUSSION |
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Top
Abstract
Introduction
Procedures
Results
Discussion
References
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The present study has been focused on Akt1 kinase, which is believed to act distal to phosphatidylinositol 3-kinase (2) and which has been reported to induce the translocation of GLUT-4 to the plasma membrane with the resulting increase in glucose uptake in 3T3-L1 adipocytes (13). The results of the present study represent the first information on the abundance and activity of Akt1 kinase in the denervated, insulin-resistant skeletal muscles. This new information and our previous observations on denervated muscles (11, 16) are summarized in Table 1. At 1 day after denervation, both soleus and plantaris muscles exhibit a pronounced decrease in the ability of insulin to stimulate 2-deoxy-D-glucose uptake. This insulin resistance occurs without any alteration in insulin binding and insulin-stimulated activity of the insulin receptor tyrosine kinase (11). This agrees with observations of others (5). There is also no alteration in the insulin-stimulated activity of phosphatidylinositol 3-kinase (11). The present study demonstrates that there is also no change in the ability of insulin to stimulate the activity of Akt1 kinase. These data indicate that 1 day after denervation there is a clear dissociation between the markedly diminished 2-deoxy-D-glucose uptake in response to insulin and the upstream events involved in the stimulation of glucose uptake by insulin. It is unclear how many signaling steps exist between the activation of Akt1 kinase and the appearance of GLUT-4 at the plasma membrane. Because the abundance of GLUT-1 and GLUT-4 in 1-day postdenervation muscles is not different from control muscles (11), the site of the defect(s) underlying the insulin resistance at this interval is in signaling steps downstream from Akt1 kinase.
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At 3 days after denervation, the parameters relevant to insulin
signaling in muscles differ from day
1, and there is also a difference in manifestations of
insulin resistance between soleus and plantaris muscles (Table
1). At 3 days after denervation, soleus muscle is unresponsive to
insulin and does not show any increase in
2-deoxy-D-glucose uptake after
the administration of the hormone. In contrast, plantaris muscle
exhibits a pronounced increase in basal 2-deoxy-D-glucose
uptake and a reduced increment in uptake in response to insulin. The
sum of these two components results in uptake that does not differ from
the absolute level of insulin-stimulated
2-deoxy-D-glucose uptake in
control muscles. Despite the different manifestations of insulin
resistance in denervated soleus and plantaris muscles at the 3-day
interval, both soleus and plantaris muscles exhibit comparable
decreases in insulin-stimulated activities of insulin receptor tyrosine kinase (35 and 44%, respectively) and
phosphatidylinositol 3-kinase (65 and 41%, respectively)
(11). The present study demonstrates that these muscles also show
comparable decreases in insulin-stimulated activity of Akt1 kinase
(87 and 71%, respectively). Even though the degree of
inhibition of insulin-stimulated activity of Akt1 kinase in denervated
soleus and plantaris muscles could virtually account for the degree of
reduction in the insulin-induced increment in
2-deoxy-D-glucose uptake in
these respective muscles, there is another level of regulation
contributing to the observed changes. Studies by this laboratory have
shown a pronounced decrease in the content of GLUT-4 in soleus and
plantaris muscles 3 days after denervation (11). In addition, an
increase in GLUT-1 abundance in plantaris muscle has been observed at
this interval (11). These findings agree with observations by Henriksen
et al. (12), Block et al. (3), and Coderre et al. (8). The increase in GLUT-1 abundance is consistent with the augmented basal
2-deoxy-D-glucose uptake in
plantaris muscle at 3 days after denervation.
The present study also demonstrates that insulin-stimulated 2-deoxy-D-glucose uptake by slow-twitch and fast-twitch muscles is directly proportional to the abundance and insulin-stimulated activity of Akt1 kinase in the given muscle. Thus soleus muscle, a slow-twitch muscle, which exhibits a high abundance and insulin-stimulated activity of Akt1 kinase, also shows a high insulin-stimulated 2-deoxy-D-glucose uptake. In contrast, plantaris muscle, a fast-twitch muscle, which has, on the average, 52% lower abundance of Akt1 kinase and 45% lower insulin-stimulated activity of Akt1 kinase compared with soleus, also exhibits 47% lower insulin-stimulated 2-deoxy-D-glucose uptake than soleus muscle. This close, direct correlation between the magnitude of insulin-stimulated activity of Akt1 kinase and the level of glucose uptake in muscles with different fiber populations provides indirect support for the role of Akt1 kinase in insulin-stimulated glucose uptake by skeletal muscles in vivo.
Because decreased availability of energy diminishes cellular responsiveness to insulin (20), we have previously measured ATP and related substances in calf muscles of rats 3 days after a single hindlimb denervation (16). The denervated calf muscles, frozen in situ, exhibited slightly higher ATP and creatine phosphate levels and unchanged ADP and AMP levels compared with the contralateral sham muscles, demonstrating that denervated muscles are not energy deficient (16). It is also noteworthy that insulin fails to stimulate 2-deoxy-D-glucose uptake and glycogen synthesis in soleus muscles of hindlimbs immobilized for 1 day (14). This suggests that denervation-induced insulin resistance in muscle may be because of muscle inactivity rather than denervation per se.
Perspectives
The single hindlimb denervation model has several important advantages for studying the mechanisms of insulin resistance. The development of insulin resistance is rapid and highly reproducible. The presence, in the same animal, of muscles that exhibit insulin resistance (denervated hindlimb) and muscles that respond to insulin in a normal fashion (contralateral sham, control hindlimb) provides an internal control and decreases variability of results. Perfusion of both hindlimbs with the same blood in vivo eliminates differences in plasma concentrations of metabolic substrates, hormones, and cytokines as potential causal or contributing factors in the development of insulin resistance. This creates "cleaner" conditions for investigating cellular mechanisms underlying the denervation-induced insulin resistance in muscle. To date, there is no scientific explanation for insulin resistance in muscles at 1 day after denervation. Consequently, further studies on denervated muscles have a potential to provide qualitatively new information on the mechanism of insulin action.| |
FOOTNOTES |
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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. §1734 solely to indicate this fact.
Address for reprint requests: J. Turinsky, Dept. of Physiology and Cell Biology, Mail Code 134, Albany Medical College, 47 New Scotland Ave., Albany, NY 12208.
Received 24 March 1998; accepted in final form 14 July 1998.
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Top
Abstract
Introduction
Procedures
Results
Discussion
References
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