Departments of 1 Physiology and Biophysics and 2 Anatomy and Cell Biology, University of Calgary Health Sciences Centre, Calgary, Alberta, Canada T2N 4N1
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A
sustained K+ current (Iss) is
attenuated in ventricular cells from streptozotocin (STZ)-induced
diabetic rats. The in vitro addition of insulin to isolated cells
augments Iss in a process that is blocked by
disrupting either actin microfilaments (with cytochalasin D) or
microtubules (with colchicine). When these agents are added at
progressively later times, the effect of insulin becomes evident in a
time-dependent manner. Iss is also augmented by
insulin in control cells in a cytoskeleton-dependent manner. However,
in contrast to diabetic cells, cytoskeleton-dependent augmentation of
Iss by insulin occurs at a considerably faster rate in control cells. Immunofluorescent labeling shows a reduced density of -tubulin in diabetic cells, particularly in perinuclear regions. In vitro insulin replacement or in vivo insulin injections given to STZ-treated rats enhances
-tubulin density. These results suggest an impairment of cytoskeleton function and structure under insulin-deficient conditions, which may have implications for cardiac function.
cardiac potassium channels; microtubules; actin microfilaments
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
CARDIAC CONTRACTION IS INITIATED by an electrical signal, the action potential. A number of ionic currents that underlie the action potential determine its configuration and duration (22). Several outward K+ currents are responsible for termination of the action potential plateau and repolarization of the membrane potential (2). It is now recognized that variations in action potential repolarization are a major source of cardiac arrhythmias (35). Furthermore, variations in action potential duration (such as those caused by changes in K+ currents) can indirectly affect the force of contraction by determining the duration of Ca2+ influx (5). Because only very small currents flow during the plateau phase of the action potential, even slight changes in current magnitude can have a dramatic impact on action potential duration (22). In the rat heart, there is a dynamic interplay of several conductances that contribute to the repolarization of the ventricular action potentials. Although the currents involved have been well characterized (2, 9), the exact contribution of each current to the repolarization process is unclear. Potentially, a reduction in any of the outward currents may prolong the action potential.
Diabetes mellitus is an increasingly common disease, with a >5% incidence in the adult population in Western countries (15). Cardiovascular complications are common and are the leading cause of diabetes-related mortality (15, 39). Among the common complications are changes in the electrocardiogram (1) and the development of cardiac arrhythmias (26). Underlying these are changes in the action potential and some of the ion currents associated with it (11, 16, 33).
We and others have reported (11, 16, 31-33) the attenuation of two cardiac K+ currents in ventricular myocytes from insulin-deficient (type 1) diabetic rats. This attenuation leads to a prolongation of the action potential (16, 33), which may underlie the prolongation of the Q-T interval observed in the electrocardiogram of humans with type 1 diabetes (1). These K+ currents can be restored to normal by in vitro incubation (>5 h) of isolated myocytes with insulin. The working hypothesis consistent with this and previous data by us and others (11, 16, 32) is that insulin has a tonic regulatory effect on the density of two Ca2+-independent K+ currents: a transient, inactivating current (It) and a sustained, noninactivating current (Iss) (2). Insulin deficiency leads to a decline in the density of these currents, which can be reversed by adding insulin to cells in vitro. This effect occurs after a lag period of >5 h and can be blocked by inhibiting protein synthesis with cycloheximide or by disrupting the actin microfilaments with cytochalasin or the microtubules with colchicine (32). This suggests that addition of insulin to isolated cardiac cells from insulin-deficient diabetic rats triggers the synthesis of new channels. These are then transported to the cell membrane with the aid of the actin and microtubular networks. These two networks are known to interact (8) with protein transport to the cell membrane requiring both components (7). This is consistent with data obtained by Nagaya and Papazian (19) indicating that channel assembly occurs in the endoplasmic reticulum before transport of the channel to the membrane.
Insulin has been suggested to play a key regulatory role in the functional organization of actin microfilaments (14, 37). The actin network is an essential mediator in the action of insulin, leading to recruitment of preformed glucose transporters and their translocation to the cell membrane (38).
The microtubules are also targets of insulin (3, 12, 24). Thus many cellular effects of insulin may depend on the functional integrity and organization of the cytoskeleton, as indeed has been suggested (32, 38). A chronic insulin deficiency could lead to impairment in the organization of the cytoskeleton, as has been suggested previously (17, 27, 28). This could entail a compromised or slower action of insulin in cells from chronically insulin-deficient animals on reexposure to insulin.
The present work was designed to test the hypothesis that cytoskeleton-dependent effects of insulin on K+ currents follow a different time course in cardiac myocytes from control and diabetic rats. Because in control myocytes insulin (added in vitro) was found (32) to enhance only Iss (but not It), the comparison between normal and diabetic conditions was done by measuring the timing of insulin effects on Iss. The time course of insulin action was measured by disrupting the cytoskeleton at progressively later times after the addition of insulin.
The results show that the cytoskeleton-dependent action of insulin
occurs much more rapidly in control myocytes. Immunofluorescent labeling of -tubulin, a major component of microtubules, indicates that insulin deficiency results in a marked reduction in its density and distribution. In combination, these results suggest that changes in
cytoskeleton structure and function occur during chronic insulin deficiency. This affects the expression and function of membrane ion
channels and may underlie some of the complications associated with
type 1 diabetes.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
All experiments were done in accordance with the guidelines of the Animal Care Committee of the University of Calgary.
Animals.
Sprague-Dawley rats (200-250 g) were used as controls or after a
single injection of streptozotocin (STZ, 100 mg/kg iv) 6-12 days
before the experiments. STZ destroys pancreatic -cells and leads to
insulin deficiency and hyperglycemia (31-33). Another group of rats received insulin replacement (8 U/kg sc daily, from day 1 of STZ injection). Measurements of plasma levels of
glucose and insulin verified the diabetic status of the rats.
Cell isolation. Single right ventricular myocytes were prepared by enzymatic dispersion in the following manner. Rats were heparinized (2,400 U/kg ip) and anesthetized by methoxyflurane inhalation. After cervical dislocation, the hearts were removed and cannulated on a Langendorff apparatus. Coronary perfusion was performed (at 37°C, 70 cmH2O pressure) initially with a solution consisting of (in mM) 121 NaCl, 5.4 KCl, 2.8 sodium acetate, 1 MgCl2, 1 CaCl2, 5 Na2HPO4, 24 NaHCO3, and 5 glucose bubbled with 95% O2-5% CO2. After 5 min, the solution was changed to a similar solution with Ca2+ omitted. This was followed after 10 min by the same Ca2+-free solution containing 20 mM taurine, 40 µM CaCl2, 10 U/ml collagenase (Yakult Honsha, Tokyo, Japan), and 0.01 mg/ml protease (type XIV, Sigma). After 7-8 min in the enzyme-containing solution, the free wall of the right ventricle was dissected and cut into smaller pieces for further incubation in the Ca2+-free solution, also containing collagenase (50 U/ml), protease (0.1 mg/ml), 0.1 mM CaCl2, and albumin (5 mg/ml). After incubation in a shaker bath at 37°C, cells were collected over the next 20-40 min and stored in the Ca2+-free solution, which contained 20 mM taurine, 0.1 mm CaCl2, and 5 mg/ml albumin (no enzymes). Cell viability was assessed by appearance (rod-shaped, striated, clear borders) and function (stability in normal physiological Ca2+: poorly functioning cells are leaky and contract in 1 mM Ca2+). The yield of viable cells was typically 60-80% of that of cells from control and diabetic rats.
Current recordings.
Aliquots of cells were placed in a 1-ml chamber on the stage of an
inverted microscope and superfused with a solution containing (in mM)
150 NaCl, 5.4 KCl, 1 CaCl2, 1 MgCl2, 5 HEPES,
and 5.5 glucose, with pH adjusted to 7.4 with NaOH. CdCl2
(0.3 mM) was added to inhibit the L-type Ca2+ current.
Currents were recorded (at 20-22°C) using the whole cell suction
electrode method. Pipettes were filled with a solution containing (in
mM) 110 potassium aspartate, 30 KCl, 4 Na2ATP, 1 MgCl2, 10 EGTA, 1 CaCl2, and 5 HEPES, with pH
adjusted to 7.2 with KOH. Electrode resistance was 2-4 M.
Correction was made for the liquid junction potential created in these
conditions (~10 mV). Series resistance was kept to a minimum by using
low-resistance electrodes and by electronic compensation. The focus of
these experiments was the sustained, quasi-steady-state
(noninactivating) current Iss, which was
characterized in detail by Apkon and Nerbonne (2).
Iss was measured at the end of 500-ms pulses,
given from a holding potential of
80 mV, to potentials ranging from
30 to +50 mV. These pulses also elicited the transient outward
current It. These two currents are carried
through different ion channels (21). However, whereas the
exact molecular nature of It has been
established, the molecular nature of Iss remains
elusive (21). A third K+ current, elicited by
pulses to potentials ranging from
110 to
40 mV, is the background
inwardly rectifying current (IK1), which was
also measured at the end of 500-ms pulses. Because insulin does not
affect this current, it can be used as a monitor of changes in series
resistance during recordings. An increase in series resistance during
recording will reduce the amplitude of this current. When the change
was >10%, the cell was discarded.
Indirect immunohistochemistry.
Cells were deposited on coverslips by aliquoting a small volume of
solution into a Plexiglas chamber mounted with wax on the coverslip.
The chamber-coverslip unit was then placed in a tabletop centrifuge
operated at 3,003 g for 1 min. Subsequently, the chamber was
removed, and the coverslip containing the sample was fixed in methanol
for 10 min and air-dried. The samples were then rehydrated in
phosphate-buffered saline (PBS) and incubated for 30 min at 37°C with
primary antibody (-tubulin; Sigma). The samples were then washed in
PBS and incubated for an additional 30 min at 37°C with a
Cy3-conjugated donkey anti-mouse IgG (H + L) secondary antibody
(Jackson Labs, Mississauga, ON, Canada). Specimens were counterstained
with 4',6-diamidino-2-phenylindole, mounted in 90% glycerol containing
paraphenylenediamine, and observed using a Zeiss Axiophot fluorescence
microscope. Images were recorded on Ilford HP-5 film, using an FX-35A
camera (×40 objective). Exposure times were set automatically by a
Nikon HFX-II exposure meter. Differences in fluorescence between cells
are thus a function of reactivity with the antibody and not
experimental artifacts. This method did not enable a precise
quantification of
-tubulin content. However, a large number of cells
were visually divided into three categories on the basis of the amount
of
-tubulin surrounding the nucleus, which was easily identifiable
with the 4',6-diamidino-2-phenylindole staining. The three categories
included cells in which the nuclei were completely surrounded by
tubulin, cells in which the nuclei were partially surrounded, or cells with nuclei without surrounding tubulin. These categories allowed a
clear distinction among cells from the different groups (see RESULTS).
Drugs. Drugs were prepared as stock solutions and frozen until the final dilution before use. Cytochalasin D, STZ, and insulin (from bovine pancreas) were purchased from Sigma. Novolin ultralente insulin (Novo Nordisk, Bagsvaerd, Denmark) was used for in vivo insulin injections.
Statistics. A two-tailed t-test was used for comparison of two experimental groups. P < 0.05 was considered statistically significant. When three groups were compared, one-way ANOVA was done, using a Bonferroni multiple comparisons test.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Experimental protocols.
In all experiments, cells were divided into untreated and treated
groups, with insulin added to the appropriate groups soon after cell
isolation. In these experiments we used 100 nM insulin, although we
have reported that current augmentation occurs with 1 and 10 nM insulin
as well (32). Current magnitudes from individual cells are
variable. Thus, for every treatment group, recordings must be made from
many cells, and the current magnitudes must be averaged. Current
amplitudes are normalized for cell size by dividing by cell
capacitance, so that current densities are used for comparison. The
augmentation of K+ currents by insulin can be measured in
individual cells only 5 h (or more) subsequent to its addition.
Because of current amplitude variability, recordings must be made for
several hours (>5 h) to collect data from a sufficient number of
cells. Typically, these measurements were made between 5 and 11 h
after insulin addition. The protocols described below involved
recordings from cells exposed to insulin (as well as other agents) over
prolonged periods. Current magnitudes in some cells were measured at
shorter times of exposure to insulin than others. Thus it was important to ensure that once insulin augmented Iss (after
>5 h), the current amplitudes reached a plateau and were stable
thereafter. Figure 1 shows that cells
exposed to insulin for 5-7 or 7.5-11 h exhibited a similar
degree of current augmentation by insulin. This was true for diabetic
and control cells, although the currents (with and without insulin)
were smaller under diabetic conditions.
|
Diabetic conditions.
In earlier experiments, we showed (32) that, under
insulin-deficient diabetic conditions, addition of 1 µM cytochalasin D 1 h after insulin (100 nM) completely abolishes the enhancement of It and Iss by insulin.
The present experiments showed that the addition of cytochalasin D at
increasingly later times after insulin enabled the cells to develop
insulin effects (augmentation of Iss and
It) in a time-dependent manner. Figure
2A shows that, whereas at
1 h after insulin cytochalasin D is completely effective in
preventing any current augmentation by insulin, addition of cytochalasin D 5 h after insulin results in an enhancement of It and Iss by insulin to
the same extent as with insulin alone. Figure 2B shows the
current densities for Iss before insulin
addition and with insulin in the presence of cytochalasin D added 2, 4, and 5 h after insulin (in all cases, insulin was present for
5-11 h and cytochalasin D for 1 h). A clear progression of the
increase in current density by insulin can be seen for later additions of cytochalasin D.
|
Control cells. Insulin is an important regulator of cytoskeleton organization and function. We therefore postulated that a chronic deficiency in insulin would alter the function of cytoskeleton components. Because insulin augments cardiac K+ currents in a cytoskeleton-dependent manner, we tested whether the kinetics of insulin action differ in cells from control animals, which have normal insulin levels. The following experiments compared the effects of insulin in control cells with those described above in diabetic cells. In previous work, we found that, in control cells, insulin augments Iss but not It. Presumably, It saturates at lower concentrations of insulin than Iss, so that, in myocytes from normal rats, insulin can still augment Iss, but not It. Thus the comparison of control and diabetic conditions focused on Iss.
The cycloheximide dependence of the effect of insulin on Iss (implying induction of channel protein synthesis) was previously shown only in STZ-diabetic rats but had not been established in control cells. In the present experiments, the effects of cycloheximide on insulin action were also tested in control cells. Cycloheximide (2 µM) was added 30 min before insulin, and Iss was measured
|
|
|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Summary of findings.
The results presented here demonstrate several novel findings. First,
it is shown that, by timed intervention with agents that disrupt
different elements of the cytoskeleton, it is possible to follow the
progression of insulin action on the functional expression of a protein
(K+ channel) at the cell membrane. Thus Figs. 2-5 show
that, under control and insulin-deficient diabetic conditions, the
augmentation of a K+ current by insulin is blocked by
cytochalasin D or colchicine but that this inhibition can be relieved
by adding these agents at increasingly later times after insulin.
Second, this approach enabled the distinction of differences between
normal and pathological (diabetic) conditions. As shown in Figs. 4 and
5, the enhancement of Iss by insulin occurs much
more rapidly in normal myocytes. This is true for the effects of
insulin with cytochalasin D and colchicine. The slower effects of
insulin in cells from insulin-deficient rats may be linked to the
reduced density of microtubules, as illustrated by -tubulin labeling
(Figs. 6-8).
Significance and implications. These results greatly support earlier suggestions that insulin plays a major role in maintaining the structure and function of the microtubule system (12, 13, 24). Insulin deficiency has been suggested to reduce levels of tubulin mRNA and reduce tubulin density in axons (17, 18, 28). Because a major function of the microtubules is to facilitate intracellular trafficking, an insulin deficiency is expected to impair translocation between cellular compartments. This was indeed shown to occur in diabetic neuropathy, in which axonal transport is impaired (34). This effect, which is reversible and preventable by insulin treatment (34), has been linked to a reduction in the amount and density of microtubules (28). The present results show a reduction in microtubule density in cardiac myocytes as well and suggest that the translocation of newly synthesized ion channels to the cell membrane is also impaired in insulin-deficient conditions. Addition of insulin (in vivo or in vitro) restores current magnitude as well as microtubule density.
The enhancement of K+ currents by insulin was suggested earlier to involve the synthesis of new channel protein and its translocation to the membrane in a process dependent on elements of the cytoskeleton (but see Limitations). The present results are in agreement with recent work by Nagaya and Papazian (19), who showed that K+ channelLimitations.
We do not yet have direct evidence for an increase in channel protein
by insulin. The effects of insulin are blocked by cycloheximide, which
inhibits all protein synthesis: it is possible that it is accessory
proteins that are stimulated by insulin, or cytoskeleton components,
rather than channel proteins. The fact that 6 h are required before
current augmentation is seen suggests that transcription and
translation are involved, but this is not yet proven. One limitation in
addressing this issue in regard to Iss is that
this current is complex, consisting of several components
(9), and not very amenable to pharmacological manipulation
(2). It is also not yet known which Kv channel
isoforms contribute to the macroscopic current (21). This
impedes the investigation of detailed mechanisms involved in insulin
effects on the individual channel components that underlie
Iss. Another possible interpretation for the
difference in the rate of insulin action is that colchicine and
cytochalasin D permeate control and diabetic cells at a different rate,
giving different rates of insulin action on the basis of the different
timing of cytoskeleton disruption. However, the different
-tubulin
fluorescence in control and diabetic cells suggests that there are
major structural differences and that differences in permeability of
disrupting agents do not play a major role.
![]() |
ACKNOWLEDGEMENTS |
---|
This work was supported by a grant from the Canadian Diabetes Association in honor of Mary Selina Jamieson.
![]() |
FOOTNOTES |
---|
Address for reprint requests and other correspondence: Y. Shimoni, Dept. of Physiology and Biophysics, Health Sciences Centre, University of Calgary, 3330 Hospital Dr. NW, Calgary, AB, Canada T2N 4N1 (E-mail: shimoni{at}ucalgary.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 8 December 2000; accepted in final form 16 April 2001.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Airaksinen, KEJ
Electrocardiogram of young diabetic patients.
Ann Clin Res
17:
135-138,
1985[ISI][Medline].
2.
Apkon, M,
and
Nerbonne JM.
Characterization of two distinct depolarization-activated K+ currents in isolated adult rat ventricular myocytes.
J Gen Physiol
97:
973-1011,
1991[Abstract].
3.
Caron, JM.
Alteration of microtubule physiology in hepatocytes by insulin.
J Cell Physiol
138:
603-610,
1989[ISI][Medline].
4.
Chen-Zion, M,
Livnat T,
and
Beitner R.
Effects of long-term streptozotocin diabetes on cytoskeletal and cytosolic phosphofructokinase and the levels of glucose 1,6-biphosphate and fructose 2,6-biphosphate in different rat muscles.
Biochem Med Metab Biol
53:
137-144,
1994[ISI][Medline].
5.
Clark, RB,
Bouchard RA,
and
Giles WR.
Action potential duration modulates calcium influx, Na+-Ca2+ exchange, and intracellular calcium release in rat ventricular myocytes.
Ann NY Acad Sci
779:
417-429,
1996[Abstract].
6.
Eaker, EY,
Angelastro JM,
Purich DL,
and
Sninsky CA.
Evidence against impaired brain microtubule protein polymerization at high glucose concentration or during diabetes mellitus.
J Neurochem
56:
208-2093,
1991.
7.
Fath, KR,
Mamajiwalla SN,
and
Burgess DR.
The cytoskeleton in development of epithelial cell polarity.
J Cell Sci
S17:
65-73,
1993.
8.
Goode, BL,
Drubin DG,
and
Barnes G.
Functional cooperation between the microtubule and actin cytoskeletons.
Curr Opin Cell Biol
12:
63-71,
2000[ISI][Medline].
9.
Himmel, H,
Wettwer E,
Li Q,
and
Ravens U.
Four different components contribute to outward current in rat ventricular myocytes.
Am J Physiol Heart Circ Physiol
277:
H107-H118,
1999
10.
Janmey, PA.
The cytoskeleton and cell signaling: component localization and mechanical coupling.
Physiol Rev
78:
763-781,
1998
11.
Jourdon, P,
and
Feuvray D.
Calcium and potassium currents in ventricular myocytes from diabetic rats.
J Physiol (Lond)
470:
411-429,
1993[Abstract].
12.
Kadowakai, T,
Fujita-Yamaguchi Y,
Nishida E,
Takaku F,
Akiyama T,
Kathuria S,
Akanuma Y,
and
Kasuga M.
Phosphorylation of tubulin and microtubule-associated proteins by the purified insulin receptor kinase.
J Biol Chem
260:
4016-4020,
1985[Abstract].
13.
Kapeller, R,
Toker A,
Cantley LC,
and
Carpenter CL.
Phosphoinositide 3-kinase binds constitutively to /
-tubulin and binds to
-tubulin in response to insulin.
J Biol Chem
270:
25985-25991,
1995
14.
Khayat, ZA,
Tong P,
Yaworsky K,
Bloch RJ,
and
Klip A.
Insulin-induced actin filament remodeling colocalizes actin with phosphatidylinositol 3-kinase and GLUT4 in L6 myotubes.
J Cell Sci
113:
279-290,
2000
15.
Laakso, M.
Hyperglycemia and cardiovascular disease in type 2 diabetes.
Diabetes
48:
937-942,
1999[Abstract].
16.
Magyar, J,
Rusznak Z,
Szentesi P,
Szucs G,
and
Kovacz L.
Action potentials and potassium currents in rat ventricular muscle during experimental diabetes.
J Mol Cell Cardiol
24:
841-853,
1992[ISI][Medline].
17.
McLean, WG.
The role of axonal cytoskeleton in diabetic neuropathy.
Neurochem Res
22:
951-956,
1997[ISI][Medline].
18.
McLean, WG,
Pekiner C,
Cullum NA,
and
Casson IF.
Posttranslational modifications of nerve cytoskeletal proteins in experimental diabetes.
Mol Neurobiol
6:
225-237,
1992[ISI][Medline].
19.
Nagaya, N,
and
Papazian D.
Potassium channel and
subunits assemble in the endoplasmic reticulum.
J Biol Chem
272:
3022-3027,
1997
20.
Nakahira, K,
Mathos MF,
and
Trimmer JS.
Differential interaction of voltage-gated K+ channel -subunits with cytoskeleton is mediated by unique amino terminal domains.
J Mol Neurosci
11:
199-208,
1998[ISI][Medline].
21.
Nerbonne, JM.
Molecular basis of functional voltage-gated K+ channel diversity in the mammalian myocardium.
J Physiol (Lond)
525:
285-298,
2000
22.
Noble, D.
The surprising heart: a review of recent progress in cardiac electrophysiology.
J Physiol (Lond)
353:
1-50,
1984[ISI][Medline].
23.
Ramanadham, S,
Decker P,
and
Tenner TE.
Effect of insulin replacement on streptozotocin-induced effects in the rat heart.
Life Sci
33:
289-296,
1983[ISI][Medline].
24.
Ray, LB,
and
Sturgill TW.
Insulin-stimulated microtubule associated protein kinase is detectable by analytical gel chromatography as a 35-kDa protein in myocytes, adipocytes and hepatocytes.
Arch Biochem Biophys
262:
307-313,
1988[ISI][Medline].
25.
Reinila, A,
and
Akerblom HK.
Ultrastructure of heart muscle in short-term diabetic rats: influence of insulin treatment.
Diabetologia
27:
397-402,
1984[ISI][Medline].
26.
Robillon, JF,
Sadoul JL,
Benmerabet S,
Joly-Lemoine L,
Fredenrich A,
and
Canivet B.
Assessment of cardiac arrhythmic risk in diabetic patients using QT dispersion abnormalities.
Diabetes Metab
25:
419-423,
1999[ISI][Medline].
27.
Sanai, T,
Sobka T,
Johnson T,
el-Essawy M,
Muchaneta-Kubara EC,
Ben Gharbia O,
el Oldroyd S,
and
Nahas AM.
Expression of cytoskeletal proteins during the course of experimental diabetic neuropathy.
Diabetologia
43:
91-100,
2000[ISI][Medline].
28.
Scott, JN,
Clark AW,
and
Zochodne DW.
Neurofilament and tubulin gene expression in progressive experimental diabetes: failure of synthesis and export by sensory neurons.
Brain
122:
2109-2118,
1999
29.
Shi, G,
Nakahira K,
Hammond S,
Rhodes KJ,
Schechter LE,
and
Trimmer JS.
-Subunits promote K+ channel surface expression through effects early in biosynthesis.
Neuron
16:
843-852,
1996[ISI][Medline].
30.
Shields, D,
and
Arvan P.
Disease models provide insights into post-Golgi protein trafficking, localization and processing.
Curr Opin Cell Biol
11:
489-494,
1999[ISI][Medline].
31.
Shimoni, Y,
Ewart HS,
and
Severson D.
Type I and II models of diabetes produce different modifications of K currents in rat heart: role of insulin.
J Physiol (Lond)
507:
485-496,
1998
32.
Shimoni, Y,
Ewart HS,
and
Severson D.
Insulin stimulation of rat ventricular K+ currents depends on the integrity of the cytoskeleton.
J Physiol (Lond)
514:
735-745,
1999
33.
Shimoni, Y,
Firek L,
Severson D,
and
Giles W.
Short-term diabetes alters K+ currents in rat ventricular myocytes.
Circ Res
74:
620-628,
1994[Abstract].
34.
Sidenius, P,
and
Jakobsen J.
Reversibility and preventability of the decrease in slow axonal transport velocity in experimental diabetes.
Diabetes
31:
689-693,
1982[ISI][Medline].
35.
Surawicz, B.
Ventricular fibrillation and dispersion of repolarization.
J Cardiovasc Electrophysiol
8:
1009-1012,
1997[ISI][Medline].
36.
Towbin, JA.
The role of cytoskeletal proteins in cardiomyopathies.
Curr Opin Cell Biol
10:
131-139,
1998[ISI][Medline].
37.
Tsakiridis, T,
Tong P,
Matthews B,
Tsiani E,
Bilan PJ,
Klip A,
and
Downey GP.
Role of the actin cytoskeleton in insulin action.
Microsc Res Tech
47:
79-92,
1999[ISI][Medline].
38.
Tsakiridis, T,
Vranic M,
and
Klip A.
Disassembly of the actin network inhibits insulin-dependent stimulation of glucose transport and prevents recruitment of glucose transporters to the plasma membrane.
J Biol Chem
47:
29934-29942,
1994.
39.
Veglio, M,
Borra M,
Stevens LK,
Fuller JH,
and
Perin PC.
The relation between QTc interval prolongation and diabetic complications: the EUROPDIAB IDDM complication study group.
Diabetologia
42:
68-75,
1999[ISI][Medline].
40.
Watanabe, T,
Ashikaga T,
Nishizaki M,
Yamawake N,
and
Arita M.
Association of insulin with QTc dispersion.
Lancet
350:
1821-1822,
1997[ISI][Medline].