Mechanisms of Vasorelaxation Induced by Troglitazone, a Novel Antidiabetic Drug, in the Porcine Coronary Artery
From the Division of Molecular Cardiology, Research Institute of Angiocardiology and Second Department of Internal Medicine (M.F.), Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Correspondence to Professor Hideo Kanaide, MD, PhD, Division of Molecular Cardiology, Research Institute of Angiocardiology, Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan. E-mail kanaide{at}molcar.med.kyushu-u.ac.jp
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Abstract |
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Background—Troglitazone (TRO), a novel antidiabetic drug, has been reported to decrease blood pressure and relax vascular strips. The mechanism of relaxation induced by TRO was determined in terms of Ca2+ signaling in smooth muscle cells.
Methods and Results—Front-surface fluorometry and fura 2–loaded medial strips of porcine coronary artery were used to examine the effects of TRO on cytosolic Ca2+ concentrations ([Ca2+]i) and contractions. The sustained contraction induced by 100 nmol/L U46619 was similar to that induced by 60 mmol/L K+ depolarization (60K+). TRO concentration dependently decreased [Ca2+]i and the force of these contractions. The concentration of TRO required to induce 50% inhibition of U46619-induced force (2.9 µmol/L) was significantly lower than that required in the case of 60K+-induced force (7.3 µmol/L). Replacing extracellular Ca2+ with Mn2+ gradually quenched fluorescence at 360 nm excitation. This decline was accelerated by 100 nmol/L U46619 and 30K+ to a similar extent, indicating a similar activation of Ca2+ influx. TRO completely inhibited U46619-activated influx but partly inhibited depolarization-activated influx. Cumulative applications of extracellular Ca2+ during stimulations with U46619 or 118K+ induced stepwise increases in [Ca2+]i and force. TRO shifted the [Ca2+]i-force relation to the right during both stimulations.
Conclusions—TRO relaxes coronary artery by decreasing [Ca2+]i and Ca2+ sensitivity of contractile apparatus. Inhibition of Ca2+ influx was important in decreasing [Ca2+]i. TRO more effectively inhibits receptor-operated Ca2+ influx than voltage-operated Ca2+ channels.
Key Words: vasodilation • calcium channels • diabetes mellitus • fura 2
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Introduction |
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Troglitazone (TRO), (±)-5-[4-(6-hydroxy-2,5,7,8-tetramethylchroman-2-ylmethoxy) benzyl]-2,4-thiazolidinedione, one of the thiazolidinediones, is a newly developed antidiabetic drug.1 Kellerer et al2 reported that TRO improves the response of fibroblasts to insulin impaired by high glucose and restores autophosphorylation of insulin receptors. Besides its antidiabetic effects, TRO was found to decrease blood pressure.3 4 It was reported that TRO inhibited L-type Ca2+ channels of smooth muscle and induced relaxation of arterial strips without endothelium.5 Pioglitazone, another member of the thiazolidinediones, was shown to have similar vasorelaxing effects.6 However, the mechanism of vasorelaxation induced by the thiazolidinediones has yet to be determined, especially in terms of Ca2+ signal transduction in smooth muscle.
In the present study, the mechanisms of vasorelaxation induced by TRO was elucidated by measuring the effects of TRO on cytosolic Ca2+ concentration ([Ca2+]i) and force in fura 2–loaded porcine coronary arterial medial strips. A Mn2+ quenching technique was used to directly evaluate the inhibitory effects of TRO on Ca2+ influx.
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Methods |
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Preparation of Strips of Porcine Coronary Artery and Fura 2 Loading
Left circumflex coronary arteries (20 to 30 mm from the origin) were isolated from fresh porcine hearts at a local slaughterhouse. The adventitia was trimmed away, and the endothelium was removed by rubbing it with a cotton swab. Then, the segments were cut into strips (1x5x0.1 mm). The functional loss of the endothelium was confirmed by the lack of relaxation by 1 µmol/L bradykinin.
The strips were incubated with 25 µmol/L fura 2 acetoxymethyl ester (fura 2-AM) in Dulbecco's modified Eagle medium containing 5% fetal bovine serum for 4 hours at 37°C. After loading with fura 2, the strips were equilibrated in normal physiological salt solution (PSS) for at least 1 hour at 37°C. Loading the strips with fura 2, per se, did not affect contractility.7 8
Simultaneous Measurement of [Ca2+]i
and Force
The fura 2–loaded strips were mounted vertically in a quartz
organ bath, and the isometric tension was measured as
described.9 The resting load was adjusted to 300
mg. The responsiveness of each strip to 118 mmol/L
K+ PSS was recorded as reference. The values
of developed force in 5.9 mmol/L K+ PSS (at
rest) and at steady state of contraction induced by 118 mmol/L
K+ were assigned to be 0% and 100%,
respectively.
Changes in the fluorescence intensity of the fura 2–loaded strips were monitored with a front-surface fluorometer (CAM-OF3, Japan Spectroscopic Co), as previously described.9 The fluorescence ratio was monitored as an indicator of [Ca2+]i and was expressed as a percentage, assigning the values obtained in 5.9 mmol/L K+ and in 118 mmol/L K+ PSS to be 0% and 100%, respectively. The absolute values of [Ca2+]i for 0% and 100% levels were estimated in separate measurements to be 108±27 and 715±103 nmol/L (n=10), respectively.8 10 These [Ca2+]i values are considered to be an approximation of the true [Ca2+]i value.11 Therefore, a statistical analysis of the [Ca2+]i signal was performed with the percent values.
Mn2+ Quenching Protocol
To examine the effect of TRO on the Ca2+
influx, Mn2+ quenching protocol was
used.12 In the protocol, the fluorescence
intensity at 360 nm excitation (F360) was monitored. After exposing
strips to Ca2+-free PSS, 0.3 mmol/L
Mn2+ was added, which induced a gradual decline
of F360 (Mn2+ quenching). The declines of F360
during stimulation with U46619 or K+
depolarization were examined in the absence and presence of 10
µmol/L TRO. After 20 minutes' recording of the
Mn2+ quenching, strips were exposed to 1
µmol/L ionomycin in the presence of Mn2+ for 10
minutes to obtain a minimal level of F360, which was determined to be
comparable to autofluorescence level. The fluorescence
intensity was expressed as a percentage, assigning F360 obtained just
before addition of Mn2+ and after exposure to
ionomycin to be 100% and 0%, respectively. In all experiments, strips
were pretreated with 1 µmol/L thapsigargin for 10 minutes before
the addition of Mn2+ to avoid any possible
interference by Ca2+ store sites. The
pretreatment with thapsigargin had no effect on the basal
Mn2+ influx. The F360 decline during the initial
5 minute period was fitted to the exponential decline curve with the
following
formula: F=F0e-t/
where F0 is the F360 value
at the beginning of Mn2+ quenching, t
is time in minutes, and is a time constant indicating the time
required for F360 to decline by 1/e.
Drugs and Solutions
The composition of normal PSS was as follows (mmol/L): NaCl 123,
KCl 4.7, NaHCO3 15.5,
KH2PO4 1.2,
MgCl2 1.2, CaCl2 1.25, and
D-glucose 11.5. High-K+ PSS was
prepared by replacing equimolar NaCl with KCl. PSS was bubbled with
95% O2 and 5% CO2. Fura
2-AM was purchased from Dojindo. Bovine serum albumin and
thapsigargin were purchased from Sigma. TRO
(C24H27NO5S,
MW 441.55, dissolved in DMSO) was donated by Sankyo Co (Tokyo, Japan).
U46619 (9,11-dideoxy-9
, 11-methanoepoxy prostaglandin
F2) was purchased from Funakoshi.
Data Analysis
The values were expressed as mean±SEM. Student's t
test was used to determine statistical significance, and ANOVA was used
to determine the concentration-dependent effect of TRO. The significant
differences in curves such as concentration-response curves and the
[Ca2+]i-force relation
curves were determined by ANCOVA. P<0.05 were considered to have
statistical significance. All data were collected by the use of a
computerized data acquisition system (MacLab, Analog Digital
Instruments).
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Results |
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Effects of TRO on [Ca2+]i and Force of Coronary Arterial Strips During U46619- and K+- Induced Contraction
Figure 1a
and 1b shows the
representative recordings of 10 µmol/L
TRO-induced decreases in the
[Ca2+]i and force during
contractions induced by 100 nmol/L U46619 and 60 mmol/L
K+, respectively. The application of U46619
induced a rapid increase in
[Ca2+]i, which reached a
peak in 5 minutes (74.0±4.4%, n=5), then slightly decreased to a
steady level within 15 minutes (64.4±2.5%, n=5), and was subsequently
sustained at similar level (60.6±1.7%, n=5 at 75 minutes). Similarly,
force rapidly developed and reached a plateau level within 15 minutes
(84.7±3.9%, n=5) and was sustained at this level (81.6±3.4%, n=5 at
75 minutes). The sustained elevation of
[Ca2+]i was not observed
in the absence of extracellular Ca2+ (Figure 5a).
TRO was applied 15 minutes after the application of U46619, which
rapidly decreased the level of both
[Ca2+]i and force (Figure 1a). By 30 minutes, 10 µmol/L TRO decreased both
[Ca2+]i and force to 0%.
The responses to 118 mmol/L K+ and U46619
were completely restored after TRO was washed out (data not shown).
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) and 60K+ (
) U46619; n=4–6,
60K+; n=3–4. Data are mean±SEM and were obtained 60
minutes after the application of TRO.
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) indicate the concentration of extracellular
Ca.2+ c and f, [Ca2+]i-force
relations obtained at plateau levels of the contractions induced by the
cumulative applications of extracellular Ca2+ during the
stimulation with 100 nmol/L U46619 (c) and 118K+ (f) in the
absence (
), and 10 µmol/L
(
) TRO (n=5). Data are mean±SEM. ** Statistically significant by
ANCOVA.
The stimulation with 60 mmol/L K+ also
induced rapid and subsequent sustained increases in
[Ca2+]i and force, which
were maintained for more than 70 minutes. The levels of
[Ca2+]i and force were
98.4±2.6% and 93.7±2.1% at 10 minutes, and 91.7±3.3% and
96.7±2.7% (n=3) at 70 minutes, respectively (Figure 1b
, 1c, and 1d).
Thus, although the
[Ca2+]i level at the
sustained phase obtained with 60 mmol/L K+
was significantly higher than that obtained with U46619, the extent of
force development was similar. When 10 µmol/L TRO was applied at
10 minutes after stimulation with 60 mmol/L
K+ (sustained phase), both
[Ca2+]i and force
decreased. Contrary to the case of U46619-induced contraction, 10
µmol/L TRO only partially inhibited the
[Ca2+]i (40.9±3.7%,
n=4) and force (23.4±2.3%, n=4) at 60 minutes after application
(Figure 1b). Figure 1c and 1d show the concentration-dependent
inhibition of [Ca2+]i and
force, respectively, by TRO obtained at 60 minutes after application
during contractions induced by 100 nmol/L U46619 and 60 mmol/L
K+. The concentration-response (force) curve
obtained with 60 mmol/L K+
(EC50, 7.26 µmol/L) is located to the
right (P<0.005) of that obtained with U46619
(EC50, 2.89 µmol/L).
Thirty mmol/L K+ induced an increase in [Ca2+]i (67.9±2.2%, n=4) that was similar to that induced by 100 nmol/L U46619 (62.1±2.1%, n=5). The [Ca2+]i levels at 60 minutes after the application of 10 µmol/L TRO during contractions induced by 30 mmol/L K+ and 100 nmol/L U46619 were 30.0±4.5% (n=4) and -3.2±1.3% (n=5), respectively (P<0.01). Again, TRO only partially inhibited [Ca2+]i elevation induced by 30 mmol/L K+.
Effect of TRO on Ca2+ Influx in Porcine Coronary
Artery
Mn2+ quenching protocol was used to directly
assess the effects of TRO on Ca2+
influx.12 In the absence of extracellular
Ca2+, application of 0.3 mmol/L
Mn2+ caused a gradual decline of fura 2
fluorescence at 360 nm excitation (F360) without any
stimulation, which fell to <50% at 
20 minutes (n=4; Figure 2a, C and 2b, F). This decline indicates
a basal passive influx of Mn2+ during the resting
state. TRO had no effect on this basal decline (data not shown). To
examine the effects of TRO on the Mn2+ influx
induced by U46619 or high K+, strips were
stimulated with 100 nmol/L U46619 or 30 mmol/L
K+ in Ca2+-free PSS, and
0.3 mmol/L Mn2+ was subsequently applied.
Both 100 nmol/L U46619 (Figure 2a, A) and 30 mmol/L
K+ (Figure 2b, D) accelerated the F360 decline to
a similar extent. During stimulation with U46619 and
K+, it took about 7 minutes to obtain a 50%
decrease. Ten µmol/L TRO completely inhibited the U46619-induced
acceleration of F360 decline (Figure 2a, B), although it only partially
inhibited K+-induced acceleration (Figure 2b, E).
The decline of F360 was fitted to a exponential curve and a time
constant was determined; 19.0±1.7 (basal decline, n=4), 11.0±1.3
(U46619-accelerated decline, n=4), 22.0±0.85 (U46619-accelerated
decline in the presence of TRO, n=4), 9.42±0.62
(K+-accelerated decline, n=4), and 12.7±1.4
(K+-accelerated decline in the presence of TRO
n=4). There was no difference in time constants between U46619- and
K+-accelerated declines in the absence of TRO.
The time constants obtained with U46619 and 30 mmol/L
K+ in the absence of TRO were both significantly
(P<0.05) smaller than those obtained in the presence of
10 µmol/L TRO. The time constant obtained with U46619 in the
presence of TRO did not significantly differ from that of the basal
decline, whereas the time constant obtained with 30 mmol/L
K+ in the presence of TRO was significantly
smaller (P<0.05).
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Effects of TRO on Increases in [Ca2+]i
and Force Induced by Histamine
Histamine (HIS) induced a rapid increase in
[Ca2+]i with a sharp peak
at 30 seconds followed by a sustained elevation that gradually declined
and developed force rapidly to a peak at 3 to 5 minutes, followed by a
gradual decline, as described7 8 (Figure 3a). When strips were treated with
10 µmol/L TRO 10 minutes before the stimulation with HIS, both
[Ca2+]i elevation and
force were inhibited (Figure 3b). It should be noted that the early
rapid phase caused by Ca2+
release8 (Figure 3c and 3d, peak) and the
declining phase (Figure 3c and 3d, 30 minutes and 60 minutes) of
[Ca2+]i elevation and
force were inhibited by TRO.
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Effects of TRO on Ca2+ release from the
intracellular store sites were further examined by the use of HIS and
caffeine as stimuli to induce two different mechanisms of
Ca2+ release. In Figure 4, representative
recordings show 10 µmol/L HIS- and 20 mmol/L
caffeine-induced increases in
[Ca2+]i and force in the
absence (Figure 4a and 4e) and presence (Figure 4b and 4f) of 10
µmol/L TRO. When the strip was exposed to
Ca2+-free PSS containing 2 mmol/L EGTA, the
[Ca2+]i level gradually
decreased to reach a steady state after 10 minutes. Subsequent
application of HIS or caffeine induced transient increases in both
[Ca2+]i and force. The
application of TRO at the time of exposure to
Ca2+-free PSS had no effect on the decreases in
[Ca2+]i observed in
Ca2+-free PSS. However, the transient increases
in [Ca2+]i and force
induced by HIS were significantly inhibited by TRO in a dose-dependent
manner (Figure 4b, 4c, and 4d). TRO, even at 10 µmol/L, had no
effect on caffeine-induced increases in
[Ca2+]i and force.
(Figures 4f, 4g, and 4h).
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Effects of TRO on the [Ca2+]i-Force
Relationships
In Figure 5, representative recordings show the effect of
TRO on the changes in
[Ca2+]i and force induced
by cumulative applications of extracellular Ca2+
during stimulation with 100 nmol/L U46619 (Figure 5a and 5b) and
118 mmol/L K+ (Figure 5d and 5e). When
U46619 was applied to the Ca2+-free PSS, there
was only a small, if any, transient rise in
[Ca2+]i, although there
was a rapid and small sustained development of force (Figure 5a).
Subsequent cumulative applications of the extracellular
Ca2+ (0 to 1.25 mmol/L) induced a stepwise
increase in [Ca2+]i and
force. As shown in Figure 5b, when TRO was added 10 minutes before
stimulation with U46619, the small sustained force developed by U46619
in Ca2+-free medium was inhibited. The levels of
force induced by 100 nmol/L U46619 without and with 3 µmol/L,
6 µmol/L, and 10 µmol/L TRO were 17.7±4.8%,
13.0±5.1%, 7.69±1.7%, and 0.29±0.7%, respectively. The subsequent
elevation of [Ca2+]i and
force induced by the cumulative applications of extracellular
Ca2+ was inhibited by TRO. Figure 5c shows
[Ca2+]i-force relation
curves during the stimulation with U46619 in the absence and presence
(3, 6, and 10 µmol/L) of TRO. TRO concentration-dependently
shifted the [Ca2+]i-force
relation curve to the right. TRO also inhibited the elevation of
[Ca2+]i and force induced
by the cumulative application of extracellular
Ca2+ during 118 mmol/L
K+ depolarization and shifted the
[Ca2+]i-force relation to
the right (Figure 5d, 5e, and 5f).
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Discussion |
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We found that a novel antidiabetic drug, TRO, relaxed the medial strips of the porcine coronary artery by decreasing [Ca2+]i and by shifting the [Ca2+]i-force relation to the right in smooth muscle. The rightward shift of [Ca2+]i-force relation indicated the decrease in Ca2+ sensitivity of the contractile apparatus as a whole. The decrease in [Ca2+]i was mainly caused by an inhibition of Ca2+ influx and partly caused by an inhibition of agonist/receptor-mediated Ca2+ release. TRO completely inhibited [Ca2+]i increase and Mn2+ influx induced by 100 nmol/L U46619, but only partially inhibited those induced by 30 mmol/L K+, although these two stimulations induced similar [Ca2+]i elevation and Mn2+ influx. This finding suggested that there was a difference in efficacy of TRO in inhibiting Ca2+ influx between stimulation with U46619 and K+ depolarization. On the other hand, although 60 mmol/L K+ induced similar force development to that obtained with 100 nmol/L U46619, TRO inhibited U46619-activated force development more potently than that induced by K+ depolarization. This observation suggests that TRO preferentially inhibits agonist-activated Ca2+ influx and force development.
A voltage-operated L-type Ca2+ channel (VOC) is one of the well-characterized Ca2+ influx pathways in smooth muscle. High K+ solution is considered to activate VOC and induce increases in [Ca2+]i. In the present study, TRO inhibited an extracellular Ca2+-dependent increase in [Ca2+]i induced by high K+ depolarization, indicating an inhibition of VOC. This finding is consistent with the reports that VOC in smooth muscle was inhibited by TRO.5 In the present study, however, we found that TRO inhibits Ca2+ influx pathways activated by agonists in preference to VOC.
There are at least 4 mechanisms to be considered for Ca2+ influx induced by agonist in vascular smooth muscle cells. First, some agonists depolarize membrane potential and activate VOC (U46619 depolarized membrane potential of porcine coronary artery13 ). Second, VOC can be activated by intracellular second messengers or by trimeric G proteins activated by agonist.14 The third mechanism is the so-called receptor-operated Ca2+ channel.15 The fourth mechanism is the capacitative Ca2+ influx pathway.16 The observed preferential inhibition of U46619-induced Ca2+ influx suggests that different mechanisms of Ca2+ influx other than VOC are involved in the U46619-induced Ca2+ influx in porcine coronary artery, and that TRO inhibits agonist-activated Ca2+ channels other than VOC. These effects of TRO on Ca2+ influx pathways in smooth muscle are similar to those observed with SKF 96365, which was reported to be an inhibitor of receptor-operated Ca2+ channels, capacitative Ca2+ entry and VOC.17 There is no similarity between the chemical structure of TRO and that of SKF 96365. The effect of TRO on the agonist-activated Ca2+ influx has to be examined in nonexcitable cells such as endothelial cells that lack VOC, before concluding that TRO inhibits the Ca2+ entry pathways other than VOC.
The present study suggests that TRO inhibits inositol trisphosphate (IP3)-induced Ca2+ release but not the caffeine-induced one (Ca2+-induced Ca2+ release mechanism). The mechanism of this inhibition of IP3-induced Ca2+ release remains unidentified. However, it is suggested that the inhibition of IP3-induced Ca2+ release may partly be linked to inhibition of agonist-induced Ca2+ influx through the capacitative Ca2+ entry.16 It is also possible that TRO inhibits either receptor–G protein interaction or phospholipase C, which then, may inhibit IP3 production. This possibility remains to be elucidated.
During the relaxations induced by TRO, the
[Ca2+]i-force
relationships of the contractions were shifted to the right.
Furthermore, TRO inhibited the sustained force development accompanied
by only a transient
[Ca2+]i increase induced
by U46619 in the Ca2+-free media (Figure 5).
These findings suggest that TRO decreases Ca2+
sensitivity of the contractile apparatus in the porcine
coronary artery. Increases in cAMP or cGMP were shown to be
linked to the decrease in Ca2+
sensitivity.7 9 18 Several kinases, such as
protein kinase C, tyrosine kinase, and rhoA-associated kinase, were
suggested to increase Ca2+
sensitivity.19 20 21 TRO was shown to improve
autophosphorylation of insulin receptor and
phosphorylation of insulin receptor substrate 1 in rat
fibroblasts impaired by high glucose.2 It is not
known whether TRO has any effect on these
phosphorylation-dependent regulations of
Ca2+ sensitivity.
The plasma concentration of TRO in healthy volunteers and NIDDM patients reached 2.56 µmol/L and 3.14 µmol/L, respectively.22 Since IC50 values of TRO to inhibit contractions induced by U46619 and K+ depolarization were not far off from their plasma concentration in clinical use, TRO can induce vasorelaxation at therapeutic concentrations. TRO decreased blood pressure in humans4 and in rats3 given long-term therapy. In a TRO-induced decrease in blood pressure, our study suggests that the direct effect of TRO on vascular smooth muscle as an inhibitor of the Ca2+ influx may be the most important mechanism.
It is concluded that TRO, at therapeutic concentrations, induced relaxation of smooth muscle by decreasing [Ca2+]i and Ca2+ sensitivity of contractile apparatus in the porcine coronary artery. The decrease in [Ca2+]i was mainly caused by the inhibition of Ca2+ influx and partly caused by the inhibition of Ca2+ release from the IP3-sensitive Ca2+ store sites. The agonist-induced Ca2+ influx was more sensitive to inhibition by TRO than that induced by high K+ depolarization, suggesting that TRO is more specific to inhibit Ca2+ entry pathways other than VOC.
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Acknowledgments |
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This work was supported in part by grants-in-aid from the Ministry of Education, Science, Sports, and Culture, Japan; by grants from The Vehicle Racing Commemorative Foundation, Kimura Memorial Heart Foundation Research Grant, Kaibara Morikazu Medical Science Promotion Foundation, Kanae Foundation for Life & Socio-Medical Science; and by a Japan Heart Foundation Research Grant. We thank Dr Timothy D. Keeley for a critical reading of the manuscript.
Received March 31, 1998; revision received July 8, 1998; accepted July 16, 1998.
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References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
-
Bressler R, Johnson DG. Pharmacological regulation
of blood glucose levels in non-insulin-dependent diabetes mellitus.
Arch Intern Med.. 1997;157:836–848.[Abstract]
-
Kellerer M, Kroder G, Tippmer S, Berti L, Kiehn R,
Mosthaf L, Haring H. Troglitazone prevents glucose-induced insulin
resistance of insulin receptor in rat-1 fibroblasts.
Diabetes.. 1994;43:447–453.[Abstract]
-
Yoshioka S, Nishino H, Shiraki T, Ikeda K, Koike H,
Okuno A, Wada M, Fujiwara T, Horikoshi H. Antihypertensive effects of
CS-045 treatment in obese Zucker rats. Metab Clin Exp.. 1993;42:75–80.
-
Ogihara T, Rakugi H, Ikegami H, Mikami H, Masuo K.
Enhancement of insulin sensitivity by troglitazone lowers blood
pressure in diabetic hypertensives. Am J Hypertens.. 1995;8:316–320.[Medline]
[Order article via Infotrieve]
-
Song J, Walsh MF, Igwe R, Ram JL, Barazi M, Dominguez
LJ, Sowers JR. Troglitazone reduces contraction by inhibition of
vascular smooth muscle cell Ca2+ currents and not
endothelial nitric oxide production.
Diabetes.. 1997;46:659–664.[Abstract]
-
Buchanan TA, Meehan WP, Jeng YY, Yang D, Chan TM,
Nadler JL, Scott S, Rude RK, Hsueh WA. Blood pressure lowering by
pioglitazone: evidence for a direct vascular effect. J Clin
Invest.. 1995;96:354–360.
-
Abe S, Kanaide H, Nakamura M. Front-surface
fluorometry with fura 2 and effects of nitroglycerin on
cytosolic calcium concentrations and on tension in the coronary
artery of the pig. Br J Pharmacol.. 1990;101:545–552.[Medline]
[Order article via Infotrieve]
-
Hirano K, Kanaide H, Abe S, Nakamura M. Effects of
diltiazem on calcium concentrations in the cytosol and on force of
contractions in porcine coronary arterial strips.
Br J Pharmacol.. 1990;101:273–280.[Medline]
[Order article via Infotrieve]
-
Ushio FM, Abe S, Kobayashi S, Nishimura J, Kanaide H.
Effects of isoprenaline on cytosolic calcium concentrations and on
tension in the porcine coronary artery. J
Physiol.. 1993;462:679–696.
[Abstract/Free Full Text]
-
Grynkiewicz G, Poenie M, Tsien RY. A new generation of
Ca2+ indicators with greatly improved
fluorescence properties. J Biol Chem.. 1985;260:3440–3450.
[Abstract/Free Full Text]
-
Miyagi Y, Kobayashi S, Nishimura J, Fukui M, Kanaide H.
Resting load regulates cytosolic calcium-force relationship of the
contraction of bovine cerebrovascular smooth muscle. J
Physiol. 1995;484(pt 1):123–137.
-
Hallam TJ, Jacob R, Merritt JE. Evidence that
agonists stimulate bivalent-cation influx into human
endothelial cells. Biochem J.. 1988;255:179–184.[Medline]
[Order article via Infotrieve]
-
Scornik FS, Toro L. U46619, a
thromboxane A2 agonist, inhibits KCa
channel activity from pig coronary artery. Am J
Physiol.. 1992;262:C708- C713.
[Abstract/Free Full Text]
-
Nelson MT, Standen NB, Brayden JE, Worley JF 3d.
Noradrenaline contracts arteries by activating
voltage-dependent calcium channels. Nature.. 1988;336:382–385.[Medline]
[Order article via Infotrieve]
-
Bolton TB. Mechanisms of action of transmitters and
other substances on smooth muscle. Physiol Rev.. 1979;59:606–718.
[Free Full Text]
-
Putney JW Jr. Capacitative calcium entry revisited.
Cell Calcium.. 1990;11:611–624.[Medline]
[Order article via Infotrieve]
-
Merritt JE, Armstrong WP, Benham CD, Hallam TJ, Jacob
R, Jaxa-Chamiec A, Leigh BK, McCarthy SA, Moores KE, Rink TJ. SK&F
96365, a novel inhibitor of receptor-mediated calcium
entry. Biochem J.. 1990;271:515–522.[Medline]
[Order article via Infotrieve]
-
Kawasaki J, Kobayashi S, Miyagi Y, Nishimura J,
Fujishima M, Kanaide H. The mechanisms of the relaxation induced by
vasoactive intestinal peptide in the porcine coronary artery.
Br J Pharmacol.. 1997;121:977–985.[Medline]
[Order article via Infotrieve]
-
Di Salvo J, Nelson SR, Kaplan N. Protein tyrosine
phosphorylation in smooth muscle: a potential coupling
mechanism between receptor activation and intracellular calcium.
Proc Soc Exp Biol Med.. 1997;214:285–301.[Abstract]
-
Kureishi Y, Kobayashi S, Amano M, Kimura K, Kanaide H,
Nakano T, Kaibuchi K, Ito M. Rho-associated kinase directly induces
smooth muscle contraction through myosin light chain
phosphorylation. J Biol Chem.. 1997;272:12257–12260.
[Abstract/Free Full Text]
-
Nishimura J, van Breemen C. Direct regulation of smooth
muscle contractile elements by second messengers. Biochem Biophys
Res Commun.. 1989;163:929–935.[Medline]
[Order article via Infotrieve]
-
Horikoshi H, Yoshioka T, Kawasaki T, Nakamura K,
Matsunuma N, Yamaguchi K, Sasahara K. Troglitazone (CS-045), a new
antidiabetic drug. Sankyo Kenkyusho Nenpo (Annu Rep Sankyo Res
Lab.).. 1994;46:1–57.The mechanisms of troglitazone-induced
vasorelaxation were investigated by measuring
[Ca2+]i and contractions in fura 2–loaded
porcine coronary artery. Troglitazone decreased
[Ca2+]i and force during sustained
contractions induced by U46619 and K+ depolarization. Thus,
inhibition of Ca2+ influx was deemed important in
troglitazone-induced relaxations. As determined by
Mn2+-induced quenching of fluorescence at 360 nm
excitation, receptor-operated Ca2+ influx was inhibited by
troglitazone more potently than voltage-operated Ca2+
channels. A rightward shift of the
[Ca2+]i-force relation during relaxation
suggested that decrease in Ca2+ sensitivity of the
contractile apparatus was also important in relaxation.
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