Department of Kinesiology, University of Waterloo, Waterloo, Ontario, N2L 3G1 Canada
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ABSTRACT |
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Insulin signaling
was examined in muscle made insulin resistant by short-term (24-h)
denervation. Insulin-stimulated glucose transport in vitro was reduced
by 28% (P < 0.05) in denervated muscle (DEN). In
control muscle (SHAM), insulin increased levels of surface-detectable
GLUT-4 (i.e., translocated GLUT-4) 1.8-fold (P < 0.05), whereas DEN surface GLUT-4 was not increased by insulin (P > 0.05). Insulin treatment in vivo induced a rapid
appearance of phospho[Ser473]Akt- in SHAM 3 min after
insulin injection. In DEN, phospho[Ser473]Akt-
also appeared at 3 min, but Ser473-phosphorylated Akt-
was 36% lower than in SHAM (P < 0.05). In addition,
total Akt-
protein in DEN was 37% lower than in SHAM (P < 0.05). Akt-
kinase activity was lower in DEN
at two insulin levels tested: 0.1 U insulin/rat (
22%,
P < 0.05) and 1 U insulin/rat (
26%,
P < 0.01). These data indicate that short-term (24-h)
denervation, which lowers insulin-stimulated glucose transport, is
associated with decreased Akt-
activation and impaired
insulin-stimulated GLUT-4 appearance at the muscle surface.
GLUT-4; soleus; tibialis anterior
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INTRODUCTION |
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SKELETAL MUSCLE IS A MAJOR SITE for insulin-dependent disposal of circulating glucose. In this tissue, insulin signaling to stimulate glucose transport occurs through a network of protein-protein interactions (26, 49) that promote GLUT-4 glucose transporter translocation from intracellular sites to T-tubules and plasma membranes (18). Insulin receptor substrate (IRS) proteins (IRS-1/IRS-2) couple insulin receptor (IR) activity to metabolic events controlled by phosphatidylinositol-3' kinase (PI 3-kinase) (2, 3). PI 3-kinase activation is a key signal that promotes GLUT-4 translocation (10, 40, 44). However, insulin-stimulated PI 3-kinase activation alone is insufficient to stimulate glucose transport (27), implying that additional signaling protein(s) beyond PI 3-kinase are involved in stimulating glucose transport.
One target of PI 3-kinase is a plecktrin homology domain containing
serine/threonine kinase Akt [protein kinase B, or related to A and C
(rac) protein kinase]. Akt lies downstream of PI 3-kinase in the
insulin-signaling pathway (9, 28) and becomes active when
phosphatidylinositol-dependent kinases PDK1 and PDK2 phosphorylate Akt
on specific kinase activation sites (14). Overexpression of constitutively active Akt protein increases GLUT-4 translocation independently of insulin stimulation in 3T3-L1 adipocytes
(31) and rat adipocytes (15). Insulin-induced
Akt- activation is thought to promote an increase in surface glucose
transporters in insulin-responsive cells and tissues (21, 31,
45). In the skeletal muscle from patients with
non-insulin-dependent diabetes mellitus, Akt-
kinase activity is
reported to be reduced in concert with a reduction in
insulin-stimulated glucose transport (33). Furthermore, in
insulin-resistant skeletal muscle of hyperglycemic Goto-Kakizaki rats,
insulin-stimulated Akt-
kinase activity is also reduced (32,
42). However, when the blood glucose concentrations in
Goto-Kakizaki rats were normalized with phlorizin treatment, Akt-
kinase activity was restored, and insulin-stimulated glucose transport
was improved (32, 42). Thus Akt-
may be a central component of insulin resistance that can develop in skeletal muscle.
We (23, 38, 39) and others (12, 19, 25, 46)
have shown that, when muscle activity is completely eliminated by severing the motor nerve (denervation), insulin-stimulated glucose transport is markedly reduced. The insulin resistance observed in
denervated muscle develops rapidly, because insulin-stimulated glucose
transport rates are decreased within a few hours after the muscles have
been denervated (~6 h) (48). After 3 days of denervation, the large reductions in the total GLUT-4 content (80%)
(23, 37, 38) and reduced insulin-stimulated PI 3-kinase activity (19) can account for a considerable fraction of
the reduced insulin-stimulated glucose transport. However, the
reduction in insulin-stimulated glucose transport observed after
24 h of denervation (19, 25) occurs before there is a
decrease in the total amount of GLUT-4 protein (4, 12, 25)
or PI 3-kinase activation (11, 19). To date, no mechanism
has been identified to account for insulin resistance in
24-h-denervated muscles.
Because Akt- has been implicated as a key insulin signaling protein
for regulating GLUT-4 translocation, we examined whether the loss of
insulin-stimulated glucose transport in short-term (24-h)-denervated
muscle, in which GLUT-4 content is not altered, is associated with
1) impaired insulin-stimulated Akt-
activation and
2) reduced GLUT-4 translocation.
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MATERIALS AND METHODS |
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Materials
Polyclonal sheep anti-rat Akt-Animals
Male Sprague-Dawley rats weighing 200-230 g were housed in a temperature-controlled environment and were maintained on a 12:12-h reverse light-dark cycle. The animals were provided with a rat chow diet ad libitum and tap water. All experimental procedures were approved by the Committee on Animal Care at the University of Waterloo.Hindlimb muscle denervations.
The hindlimb muscles in one limb were denervated as we have previously
described (38). Briefly, rats were anesthetized under halothane gas after a subcutaneous injection of buprenorphine (0.03 mg/kg) analgesic. A small superficial incision was made on one leg, the
sciatic nerve was located, and ~3 mm of the nerve were removed. A
sham operation was performed on the contralateral leg. Incisions in
both legs were closed with surgical clips, and a topical disinfectant
was applied to the skin. After rats had recovered (1 h), food and
water were provided. Experiments were performed 24 h later on
overnight-fasted rats.
Animal preparation.
Rats were anesthetized with 65 mg/kg pentobarbital sodium and placed on
a heating pad at a low temperature setting, and hindlimb muscles were
exposed by carefully cutting free the exterior skin. Soleus muscles
were removed for determination of glucose transport and surface GLUT-4
measurements. Approximately 15 min later, the descending aorta in rats
was injected with 0.1 ml saline (+0.1% BSA) plus insulin or the
equivalent volume of saline (+0.1% BSA) alone, followed by a rapid
dissection of the tibialis anterior (TA) muscle at two specific time
points (3 and 5 min) in different experiments. After the denervated and
sham TA muscles were dissected from hindlimbs, the red TA (RTA) portion
was quickly separated from the white TA compartment, immersed in liquid
N2, and kept at 80°C for later use.
Insulin-Stimulated Glucose Transport in Incubated Soleus Strips
Soleus muscles were cut into thin lengthwise strips suitable for in vitro incubations (5). Strips were preincubated for 1 h at 29°C in Krebs-Henseleit buffer (KHB) with 32 mM mannitol, 8 mM D-glucose, and 0.1% BSA. Porcine insulin was added to the incubation medium at a maximal stimulating concentration of 400 µU/ml for 30 min. Before glucose transport measurements, D-glucose was removed by washing strips twice for 5 min each in a glucose-free KHB with 38 mM mannitol and 2 mM pyruvate. The uptake of 2-deoxyglucose was determined with 2 mM pyruvate (1.5 µCi), 2-deoxy-D-[3H]glucose (1 mM and 0.1 µCi), and [14C]mannitiol (37 mM) for 10 min. Strips were removed rapidly, rinsed in 0.9% ice-cold saline, cut free of tendons, and snap frozen in liquid N2. Muscles were stored atGLUT-4 AND AKT- Determination by
Western Blotting
Total Akt- and total GLUT-4 protein.
For GLUT-4 determinations, soleus muscle was prepared as described
elsewhere (22, 29). For Akt-
determinations, RTA
muscles (50-80 mg) were homogenized in ice-cold homogenization
buffer (50 mM Tris, pH 7.5, 110 mM sodium tetrapyrophosphate, 11 mM
EDTA, 110 mM sodium fluoride, 10 mM sodium orthovanadate, 1% Triton X-100, 200 mM PMSF, 10 mg/ml aprotinin, 1 mg/ml leupeptin, and 1 mg/ml
pepstatin A). Western blotting was used to determine GLUT-4 and Akt-
content. Briefly, samples were separated by SDS-PAGE on a 12% gel and
transferred to an Immobilon membrane (Millipore) by electromembrane
transfer for 90 min. Membranes were blocked overnight in 5% nonfat dry
milk (NFDM) made in TBS (pH 7.6). Proteins were detected by incubation
of blocked membranes with an anti-GLUT-4 polyclonal immuno-A purified
antibody (1:7,000) or anti-rat Akt-
antibody (1:1,000) followed by
HRP-conjugated anti-rabbit IgG diluted (1:2,000) in TBS, pH 7.6, for
GLUT-4 detection or with HRP-labeled anti-sheep IgG diluted (1:2,000)
in 5% NFDM for Akt-
detection. GLUT-4 and Akt-
were visualized
with an enhanced chemiluminescence system (Amersham Life Science)
according to the manufacturer's instructions. Western blots were
quantified by a Macintosh LC with an Abaton scanner and appropriate
software (Scan Analysis, Biosoft, Cambridge, UK).
Surface detectable GLUT-4. The method for detection of surface GLUT-4 in skeletal muscle was adapted from a procedure used with rat adipocytes (16, 51). This method is based on the principle that exogenous trypsin cuts surface-accessible GLUT-4 at a predicted trypsin cleavage site in the exofacial loop of the GLUT-4 transporter. Trypsin-cleaved GLUT-4 appears on a blot at a lower molecular weight than native GLUT-4 protein when the fragmented GLUT-4 is detected with antibodies to the GLUT-4 carboxy terminus (16). GLUT-4 fragments migrate to 35 kDa instead of the 46-kDa position of nontrypsinized native GLUT-4. We have previously used this procedure to detect surface GLUT-4 in adipocytes (51).
To apply the method to skeletal muscle, soleus muscles were cut into strips and preincubated in vials with KHB for 45 min at 35°C. Insulin (400 µU/ml) was added to one-half of the vials for 10 min. All vials received 2 mM KCN for another 20 min to stop surface membrane proteins from recycling with internal protein pools. Strips were treated with 1 mg/ml trypsin and continued to incubate for an additional 30 min. Strips were washed (2 × 5 min) in a buffer free of exogenous trypsin with 1 mg/ml SBTI added; they were then quickly frozen in liquid N2 and stored atAkt-[Ser473] phosphorylation with in vivo
insulin treatment.
Saline- and insulin-injected rats were used to determine basal
(non-insulin-stimulated) and activated Akt-
[Ser473]
phosphorylation levels, respectively. Muscles were homogenized in ice-cold buffer 1 [150 mM NaCl, 50 mM TRIS, pH 7.5, 30 mM sodium pyrophosphate, 10 mM sodium fluoride, 1 mM dithiothreitol
(DTT), 10% (vol/vol) glycerol, 1% Triton X-100, 1 mg/ml bacitracin,
200 mM PMSF, 10 mg/ml aprotinin, 1 mg/ml leupeptin, 1 mg/ml pepstatin A, 1 µM microcystin]. Homogenates were spun at 15,000 rpm (70 Ti,
Sorvall) for 1 h at 4°C. Samples were resolved on a 6% gel by
SDS-PAGE and transferred to an Immobilon membrane (Millipore) by
electromembrane transfer for 90 min. Membranes were blocked in 5%
nonfat dry milk (1 h) and probed with
anti-phospho[Ser473]Akt-
antibody (1 h) followed by
HRP-labeled anti-sheep IgG secondary antibody (1 h).
Phospho[Ser473]Akt-
was visualized and quantified as
described above.
Measurements of Akt- Kinase Activity in Vivo
Protein Assay
All protein concentrations were determined in triplicate by bicinchoninic acid assay (Sigma), with BSA as a standard.Plasma Insulin
Insulin levels were determined with the use of an insulin radioimmunoassay kit (DPC, Los Angles, CA) according to the manufacturer's directions.Statistical Analysis
Data were analyzed by use of analysis of variance and t-test, as appropriate. All data are reported as means ± SE. ![]() |
RESULTS |
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Glucose Transport in Incubated Soleus Strips
Glucose transport was determined in soleus muscles in vitro. In addition, incubated control and denervated soleus muscles were also used to compare total GLUT-4 and the surface GLUT-4 in basal and insulin-stimulated muscles.In the absence of insulin (basal), 2-deoxyglucose transport was not
different between 24-h-denervated and control soleus muscle (P > 0.05) (Fig. 1).
Insulin treatment increased soleus muscle glucose transport 2.2-fold in
control (P < 0.01) but only 1.7-fold in denervated
soleus muscles (28% reduction, P < 0.01; Fig. 1). In
a separate experiment, when insulin-stimulated glucose transport was
determined by hindlimb perfusion, the denervated RTA muscle showed a
similar reduction (27%) in glucose transport (4.0 ± 0.28 vs.
2.92 ± 0.21 µmol · g
1 · 10 min
1, P < 0.05).
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Insulin Signaling through AKT-
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Insulin-stimulated Akt- kinase activity.
Plasma insulin concentrations were elevated to high physiological
levels or to supraphysiological levels after insulin injections (Table
1). In control muscle, 0.1-U insulin
injections increased Akt-
kinase activity (Fig. 2) 2.3-fold
(P < 0.05), whereas 1-U insulin injections increased
Akt-
kinase activity 3.4-fold (P < 0.01). In
denervated muscle, Akt-
kinase activity was found to be 22 (P < 0.05) and 26% lower (P < 0.01)
after 0.1-U and 1-U insulin injections, respectively.
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Akt-[Ser473] phosphorylation and total
immunoreactive Akt-
protein.
Insulin-stimulated Akt-
phosphorylation occurred in a time-dependent
manner (Fig. 3).
Phospho[Ser473]Akt-
protein level was significantly
higher in control muscle at 3 min (P < 0.05) than in
denervated muscle. In addition, the total Akt-
protein (Fig.
4) was decreased (
37%) in denervated muscle (P < 0.05).
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Total GLUT-4 and Translocated Surface GLUT-4
The level of total GLUT-4 was comparable in denervated and control soleus muscle (P > 0.05) (Fig. 5A). In a separate experiment, total GLUT-4 in RTA muscle was also not different in denervated muscle compared with control muscle (data not shown). The increased surface GLUT-4 availability after insulin stimulation (translocated GLUT-4) was determined by a trypsin cleavage method (Fig. 5B). Insulin increased surface GLUT-4 1.8-fold (P < 0.05) in control muscle, whereas no change in surface GLUT-4 was detected in denervated muscle (Fig. 5C).
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DISCUSSION |
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This study has shown that insulin-stimulated glucose transport is
decreased (Fig. 1) in short-term (24-h)-denervated muscle. Consistent
with previous work (4, 12), this decrease is not due to a
reduction in total GLUT-4; instead, we attribute denervation-induced insulin resistance to an impairment in Akt- activation that is associated with a concomitant reduction in insulin-stimulated GLUT-4 translocation.
Insulin activates Akt- through earlier signals that first activate
PI 3-kinase (9). Increasing Akt-
kinase activity in vivo is accomplished by the phosphatidylinositol-dependent kinases PDK1
and PDK2 (13). PDK1 and PDK2 are proposed to phosphorylate Thr308 and Ser473, respectively, on Akt-
(see review by Coffer et al., Ref. 13). Intravenous insulin injections
increase Akt-
kinase activity in rat muscle until maximum activity
is seen after 5 min (48). In our studies, maximal Akt-
kinase activity was observed after 3 min in control muscle (data not shown).
Recently, Akt- activation has been implicated as a key step in
insulin signaling in skeletal muscle (32, 33, 42). Two studies (32, 42) have shown that the decrease in
insulin-induced Akt-
activity and glucose transport was due to a
prevailing hyperglycemia, because both Akt-
activity and glucose
transport were restored to control levels once blood glucose was
normalized. Moreover, decreases in Akt activity and glucose transport
activation, reportedly caused by hyperglycemia (34), may
be due to changes in insulin-signaling events downstream from PI
3-kinase. Kurowski et al. (34) showed that, with
hyperglycemia, insulin-stimulated glucose transport is reduced in
skeletal muscle (
30%). In these muscles,
phosphotyrosine-immunoprecipitated PI 3-kinase activity and both IRS1-
and IRS2-associated PI 3-kinase activity were not altered, whereas
marked reductions in Akt activation (
60%) were observed. Therefore,
insulin resistance in skeletal muscle, in some instances (i.e., during
hyperglycemia), may be a consequence of reducing the signals from Akt.
Similar to hyperglycemia, the insulin resistance induced by denervation
may involve a defect beyond PI 3-kinase. In previous studies, there
appeared to be no defects in insulin signaling pathways (up to PI
3-kinase) in short-term (24-h)-denervated muscles (11, 19,
50). Our earlier data support the idea that PI 3-kinase
activation occurs normally in muscles denervated for 24 h, because
we found that the amount of insulin-stimulated PI 3-kinase regulatory
subunit (p85) immunoprecipitated by antiphosphotyrosine antibodies was
not decreased by denervation (50). However, our data here
show that muscle denervation decreased insulin-stimulated Akt-
kinase activity (Fig. 2). This decrease is attributable to an impaired
Akt-
activation. Denervation decreased the rate (
36%) of muscle
Akt-
phosphorylation (Fig. 3) and muscle Akt-
protein content
(
37%; Fig. 4). In contrast, Turinsky and Damrau-Abney (47) did not observe any changes in insulin-stimulated
Akt-
kinase activity in short-term (24-h)-denervated muscles. We
have no explanation for the discrepancy between our studies and their work. Nevertheless, based on our work, it may be that an inadequate insulin signaling response through Akt-
may contribute to the insulin resistance in 24-h-denervated muscles.
The lower insulin-stimulated Akt- kinase activity induced by
denervation could have occurred if impairments to the insulin signaling
mechanism, before Akt-
in the insulin signaling pathway, contributed
to impairments in Akt-
activation in denervated muscle. But because
IR bind insulin with a normal affinity (8), and denervation does not appear to affect insulin-activated IR tyrosine kinase activity 24 h after muscle denervation (19),
it is unlikely that the reduced Akt-
activation in 24-h-denervated
muscle was due to poor IR activation. Moreover, our data show that
supraphysiological plasma insulin concentrations did not further
increase Akt-
kinase activity in the denervated muscle (Fig. 2);
rather, the reductions in Akt-
kinase activity (~25% lower) were
similar at both high physiological and supraphysiological insulin
concentrations. Thus the lower insulin-stimulated Akt-
activation
response in the denervated muscle was more likely due to a signaling
change at a post-IR level rather than from insufficient IR tyrosine
kinase activation.
Another possibility is that denervations had uncoupled upstream signals
from Akt- that would impair the ability of insulin to activate
Akt-
in vivo. Because insulin-stimulated PI 3-kinase activity is not
reported to be affected in muscle denervated for 24 h (11,
19, 50), PI 3-kinase-activated signals required to activate
Akt-
in vivo were likely sufficient in denervated muscles.
Furthermore, PDK2 was unlikely to be affected by denervation, because
Akt-
[Ser473] phosphorylation still occurred in
denervated muscle, albeit at a slower rate (Fig. 3). It is more likely
that reductions in insulin-stimulated Akt-
kinase activity observed
in 24-h-denervated muscle were a consequence of lower Akt-
protein
availability in these muscles (Fig. 4). Interestingly,
Akt-
[Ser473] phosphorylation in denervated
muscle reached control levels by 5 min. Because phosphorylation on
Thr308 also contributes to Akt-
activation
(1), and both the Ser473 and
Thr308 sites require phosphorylation to obtain full Akt-
kinase activation (1), our data suggest that a diminished
Thr308 phosphorylation on Akt-
may account for the
reduced Akt-
kinase activation in 24-h-denervated muscles.
Conceivably, an impairment in Akt- activation in denervated muscles
may attenuate signals that normally induce GLUT-4 translocation. Notably, there was a discrepancy in the percent reduction between insulin-induced Akt-
activation (
25%) and GLUT-4 translocation. It is possible that additional insulin-activated mechanisms, such as
GLUT-4 trafficking or GLUT-4 membrane insertion steps, were also
affected by denervation.
The reduction in glucose transport in denervated muscle was less than would have been expected, given that GLUT-4 at the surface was not increased by insulin. Undoubtedly, reduced GLUT-4 translocation contributed to insulin resistance in our studies. A number of studies have shown that glucose transport into the cell occurs in direct proportion to the surface GLUT-4 (35, 36). However, insulin may also stimulate glucose transport without necessarily increasing the number of surface GLUT-4 transporters (43). A variety of more recent studies have revitalized the idea that the intrinsic activity of surface GLUT-4 can be increased or decreased (17, 20, 22, 24, 40, 43). We have published work (22) showing that epinephrine can markedly lower glucose transport despite an insulin-induced increase in plasma membrane GLUT-4.
We believe that the results obtained in the soleus and RTA muscles with different insulin administration procedures can be integrated. It has previously been shown that the soleus and plantaris muscles, with markedly different fiber types, respond similarly to denervation (48). Two highly oxidative muscles such as the soleus and RTA would therefore be expected to respond similarly to denervation. Moreover, both muscles here were exposed to maximally stimulating concentrations of insulin either in vitro (soleus) or in vivo (RTA). Nevertheless, it is recognized that the delivery of insulin differs in vivo and in vitro. Therefore, the extent of GLUT-4 translocation or signaling per gram of muscle may be different between these two means of providing insulin.
In summary, our data demonstrate that there is a partial reduction in
insulin-stimulated glucose transport along with a similar partial
reduction in insulin-stimulated Akt- activity in denervated muscle.
These data indicate that short-term (24-h) denervation decreased
Akt-
activation and impaired insulin-stimulated GLUT-4 appearance at
the muscle cell surface.
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ACKNOWLEDGEMENTS |
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These studies were supported by the Canadian Diabetes Association in honor of George Goodwin and by the Natural Sciences and Engineering Research Council of Canada.
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FOOTNOTES |
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Address for reprint requests and other correspondence: A.Bonen, Dept. of Kinesiology, Univ. of Waterloo, Waterloo, Ontario 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 13 December 1999; accepted in final form 16 May 2000.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Alessi, DR,
Andjelkovic M,
Caudwell FB,
Cron P,
Morrice N,
Cohen P,
and
Hemmings BA.
Mechanisms of activation of protein kinase B by insulin and IGF-1.
EMBO J
15:
6541-6551,
1996[Abstract].
2.
Backer, JM,
Myers MG, Jr,
Shoelson SE,
Chin DJ,
Sun XI,
Miralpeix M,
Hu P,
Margolis B,
Skolnik EY,
and
Schlessinger J.
Phosphatidylinositol 3'-kinase is activated by association with IRS-1 during insulin stimulation.
EMBO J
11:
3469-3479,
1992[Abstract].
3.
Backer, JM,
Myers MG, Jr,
Sun X,
Chin DJ,
Shoelson SE,
Miralpeix M,
and
White MF.
Association of IRS-1 with the insulin receptor and the phosphatidylinositol 3'-kinase: formation of binary and ternary signalling complexes in intact cells.
J Biol Chem
268:
8204-8212,
1993
4.
Block, NE,
Menick DR,
Robinson KA,
and
Buse MG.
Effect of denervation on the expression of two glucose transporter isoforms in rat hindlimb muscle.
J Clin Invest
88:
1546-1552,
1991[ISI][Medline].
5.
Bonen, A,
Clark MG,
and
Henriksen EJ.
Experimental approaches to the study of skeletal muscle metabolism: comparison of hindlimb perfusion and isolated muscle incubations.
Am J Physiol Endocrinol Metab
266:
E1-E16,
1994
6.
Bonen, A,
McDermott JC,
and
Tan MH.
Glycogenesis and glyconeogenesis in skeletal muscle: effects of pH and hormones.
Am J Physiol Endocrinol Metab
258:
E693-E700,
1990
7.
Bonen, A,
Tan MH,
Megeney LA,
and
McDermott JC.
Persistence of glucose metabolism after exercise in trained and untrained soleus muscle.
Diabetes Care
15:
1694-1700,
1992[Abstract].
8.
Burant, CF,
Lemmon SK,
Treutelaar MK,
and
Buse MG.
Insulin resistance of denervated rat muscle: a model for impaired receptor-function coupling.
Am J Physiol Endocrinol Metab
247:
E657-E666,
1984
9.
Burgering, BM,
and
Coffer PJ.
Protein kinase B (c-Akt) in phosphatidylinositol-3-OH kinase signal transduction.
Nature
376:
599-602,
1995[ISI][Medline].
10.
Cheatham, B,
Vlahos CJ,
Cheatham L,
Wang L,
Blenis J,
and
Kahn CR.
Phosphatidylinositol 3'-kinase activation is required for insulin stimulation of pp70S6 kinase, DNA synthesis, and glucose transporter translocation.
Mol Cell Biol
14:
4902-4911,
1994[Abstract].
11.
Chen, KS,
Friel JC,
and
Ruderman NB.
Regulation of phosphatidylinositol 3'-kinase by insulin in rat skeletal muscle.
Am J Physiol Endocrinol Metab
265:
E736-E742,
1993
12.
Coderre, L,
Monfar MM,
Chen KS,
Heydrick SJ,
Kurowski TG,
Ruderman NB,
and
Pilch PF.
Alteration in expression of GLUT-1 and GLUT-4 protein and messenger RNA levels in denervated rat muscles.
Endocrinology
131:
1821-1825,
1992[Abstract].
13.
Coffer, PJ,
Jin J,
and
Woodgett JR.
Protein kinase B (c-Akt): a multifunctional mediator of phosphatidylinositol 3'-kinase activation.
Biochem J
335:
1-13,
1998[ISI][Medline].
14.
Cohen, P,
Alessi DR,
and
Cross DA.
PDK1, one of the missing links in insulin signal transduction?
FEBS Lett
410:
3-10,
1997[ISI][Medline].
15.
Cong, LN,
Chen H,
Li Y,
Zhou L,
McGibbon MA,
Taylor SI,
and
Quon MJ.
Physiological role of Akt in insulin- stimulated translocation of GLUT-4 in transfected rat adipose cells.
Mol Endocrinol
11:
1881-1890,
1997
16.
Czech, MP,
and
Buxton JM.
Insulin action on the internalization of the GLUT-4 glucose transporter in isolated rat adipocytes.
J Biol Chem
268:
9187-9190,
1993
17.
Dauterive, R,
Laroux S,
Bunn RC,
Chaisson A,
Sanson T,
and
Reed BC.
C-terminal mutations that alter the turnover number for 3-O-methylglucose transport by GLUT-1 and GLUT-4.
J Biol Chem
271:
11414-11421,
1996
18.
Dombrowski, L,
Roy D,
Marcotte B,
and
Marette A.
A new procedure for the isolation of plasma membranes, T tubules, and internal membranes from skeletal muscle.
Am J Physiol Endocrinol Metab
270:
E667-E676,
1996
19.
Elmendorf, JS,
Damrau-Abney A,
Smith TE,
David TS,
and
Turinsky J.
Phosphatidylinositol 3'-kinase and dynamics of insulin resistance in denervated slow and fast muscles in vivo.
Am J Physiol Endocrinol Metab
272:
E661-E670,
1997
20.
Fisher, MD,
and
Frost SC.
Translocation of GLUT-1 does not account for elevated glucose transport in glucose-deprived 3T3-L1 adipocytes.
J Biol Chem
271:
11806-11809,
1996
21.
Hajduch, E,
Alessi DR,
Hemmings BA,
and
Hundal HS.
Constitutive activation of protein kinase B-alpha by membrane targeting promotes glucose and system A amino acid transport, protein synthesis, and inactivation of glycogen synthase kinase 3 in L6 muscle cells.
Diabetes
47:
1006-1013,
1998[Abstract].
22.
Han, X,
and
Bonen A.
Epinephrine translocates GLUT-4 but inhibits insulin-stimulated glucose transport in rat muscle.
Am J Physiol Endocrinol Metab
274:
E700-E707,
1998
23.
Handberg, A,
Megeney LA,
McCullagh KJA,
Kayser L,
Han XX,
and
Bonen A.
Reciprocal GLUT-1 and GLUT-4 expression and glucose transport in denervated muscles.
Am J Physiol Endocrinol Metab
271:
E50-E57,
1996
24.
Hansen, PA,
Wang W,
Marshall BA,
Holloszy JO,
and
Mueckler M.
Dissociation of GLUT-4 translocation and insulin- stimulated glucose transport in transgenic mice overexpressing GLUT-1 in skeletal muscle.
J Biol Chem
273:
18173-18179,
1998
25.
Henriksen, EJ,
Rodnick KJ,
Mondon CE,
James DE,
and
Holloszy JO.
Effect of denervation or unweighting on GLUT-4 protein in rat soleus muscle.
J Appl Physiol
70:
2322-2327,
1991
26.
Holman, GD,
and
Kasuga M.
From receptor to transporter: insulin signalling to glucose transport.
Diabetologia
40:
991-1003,
1997[ISI][Medline].
27.
Isakoff, SJ,
Taha C,
Rose E,
Marcusohn J,
Klip A,
and
Skolnik EY.
The inability of phosphatidylinositol 3'-kinase activation to stimulate GLUT-4 translocation indicates additional signaling pathways are required for insulin-stimulated glucose uptake.
Proc Natl Acad Sci USA
92:
10247-10251,
1995[Abstract].
28.
James, SR,
Downes CP,
Gigg R,
Grove SJA,
Holmes AB,
and
Alessi DR.
Specific binding of the Akt-1 protein kinase to phosphatidylinositol 3,4,5-triphosphate without subsequent activation.
Biochem J
315:
709-713,
1996[ISI][Medline].
29.
Johannsson, E,
Jensen K,
Gunderson K,
Dahl HA,
and
Bonen A.
Effect of electrical stimulation patterns on glucose transport in rat muscle.
Am J Physiol Regulatory Integrative Comp Physiol
271:
R426-R431,
1996
30.
Kohn, AD,
Kovacina KS,
and
Roth RA.
Insulin stimulates the kinase activity of RAC-PK, a pleckstrin homology domain containing serine/threonine kinase.
EMBO J
14:
4288-4295,
1995[Abstract].
31.
Kohn, AD,
Summers SA,
Birnbaum MJ,
and
Roth RA.
Expression of a constitutively active Akt Ser/Thr kinase in 3T3-L1 adipocytes stimulates glucose uptake and glucose transporter 4 translocation.
J Biol Chem
49:
31372-31378,
1996.
32.
Krook, A,
Kawano Y,
Song XM,
Efendic S,
Roth RA,
Wallberg-Henriksson H,
and
Zierath JR.
Improved glucose tolerance restores insulin-stimulated Akt kinase activity and glucose transport in skeletal muscle from diabetic Goto-Kakizaki (GK) rats.
Diabetes
46:
2110-2114,
1997[Abstract].
33.
Krook, A,
Roth RA,
Jiang XJ,
Zierath JR,
and
Wallberg-Henriksson H.
Insulin-stimulated Akt kinase activity is reduced in skeletal muscle from NIDDM subjects.
Diabetes
47:
1281-1286,
1998[Abstract].
34.
Kurowski, TG,
Lin Y,
Luo Z,
Tsichlis PN,
Buse MG,
Heydrick SJ,
and
Ruderman NB.
Hyperglycemia inhibits insulin activation of Akt/protein kinase B but not phosphatidylinositol 3'-kinase in rat skeletal muscle.
Diabetes
48:
658-663,
1999[Abstract].
35.
Lund, S,
Holman GD,
Schmitz O,
and
Pedersen O.
GLUT-4 content in the plasma membrane of rat skeletal muscle: comparative studies of the subcellular fractionation method and the exofacial photolabeling technique using ATB-BMPA.
FEBS Lett
30:
312-318,
1993.
36.
Lund, S,
Holman GD,
Schmitz O,
and
Pedersen O.
Contraction stimulates translocation of glucose transporter GLUT-4 in skeletal muscle through a mechanism distinct from that of insulin.
Proc Natl Acad Sci USA
92:
5817-5821,
1995
37.
Megeney, LA,
Michel RN,
Boudreau CS,
Fernando PK,
Prasad M,
Tan MH,
and
Bonen A.
Regulation of muscle glucose transport and GLUT-4 by nerve-derived factors and activity-related processes.
Am J Physiol Regulatory Integrative Comp Physiol
269:
R1148-R1153,
1995
38.
Megeney, LA,
Neufer PD,
Dohm GL,
Tan MH,
Blewett CA,
Elder GCB,
and
Bonen A.
Effects of muscle activity and fiber composition on glucose transport and GLUT-4.
Am J Physiol Endocrinol Metab
264:
E583-E593,
1993
39.
Megeney, LA,
Prasad M,
Tan MH,
and
Bonen A.
Expression of the insulin-regulatable transporter GLUT-4 is influenced by neurogenic factors.
Am J Physiol Endocrinol Metab
266:
E813-E816,
1994
40.
Quon, MJ,
Chen H,
Ing BL,
Liu ML,
Zarnowski MJ,
Yonezawa K,
Kasuga M,
Cushman SW,
and
Taylor SI.
Roles of 1-phosphatidylinositol 3'-kinase and ras in regulating translocation of GLUT-4 in transfected rat adipose cells.
Mol Cell Biol
15:
5403-5411,
1995[Abstract].
41.
Shimizu, Y,
Satoh S,
Yano H,
Minokoshi Y,
Cushman SW,
and
Shimazu T.
Effects of noradrenaline on the cell-surface glucose transporters in cultured brown adipocytes: novel mechanism for selective activation of GLUT-1 glucose transporters.
Biochem J
330:
397-403,
1998[ISI][Medline].
42.
Song, XM,
Kawano Y,
Krook A,
Ryder JW,
Efendic S,
Roth RA,
Wallberg-Henriksson H,
and
Zierath JR.
Muscle fibre-type specific defects in insulin signal transduction to glucose transport in diabetic GK rats.
Diabetes
48:
664-670,
1999[Abstract].
43.
Sweeney, G,
Somwar R,
Ramlal T,
Volchuk A,
Ueyama A,
and
Klip A.
An inhibitor of p38 mitogen-activated protein kinase prevents insulin-stimulated glucose transport but not glucose transporter translocation in 3T3-L1 adipocytes and L6 myotubes.
J Biol Chem
274:
10071-10078,
1999
44.
Tanti, J,
Gremeaux T,
Grillo S,
Calleja V,
Klippel A,
Williams LT,
Van Obberghen E,
and
Le Marchand-Brustel Y.
Overexpression of a constitutively active form of phosphatidylinositol 3'-kinase is sufficient to promote GLUT-4 translocation in adipocytes.
J Biol Chem
271:
25227-25232,
1996
45.
Tanti, JF,
Grillo S,
Gremeaux T,
Coffer PJ,
Van Obberghen E,
and
Le Marchand-Brustel Y.
Potential role of protein kinase B in glucose transporter 4 translocation in adipocytes.
Endocrinology
138:
2005-2010,
1997
46.
Turinsky, J.
Dynamics of insulin resistance in denervated slow and fast muscles in vivo.
Am J Physiol Regulatory Integrative Comp Physiol
252:
R531-R537,
1987
47.
Turinsky, J,
and
Damrau-Abney A.
Akt-1 kinase and dynamics of insulin resistance in denervated muscles in vivo.
Am J Physiol Regulatory Integrative Comp Physiol
275:
R1425-R1430,
1998
48.
Walker, KS,
Deak M,
Paterson A,
Hudson K,
Cohen P,
and
Alessi DR.
Activation of protein kinase B isoforms by insulin in vivo and by 3-phosphoinositide-dependent protein kinase-1 in vitro: comparison with protein kinase B-alpha.
Biochem J
331:
299-308,
1998[ISI][Medline].
49.
White, MF.
The insulin signaling system and the IRS proteins.
Diabetologia
40:
s2-s17,
1997[ISI][Medline].
50.
Wilkes, JJ,
and
Bonen A.
Denervation impairs GLUT-4 arrival in the plasma membrane which is associated with lower total Akt- quantity but not phosphotyrosine immunoprecipitated IRS-1 (Abstract).
FASEB J
12:
355,
1998.
51.
Wilkes, JJ,
DeForrest LL,
and
Nagy LE.
Chronic ethanol feeding in a high fat diet decreases insulin-stimulated glucose transport in rat adipocytes.
Am J Physiol Endocrinol Metab
271:
E477-E484,
1996