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1 Laboratory for Physiology and 2 Department of Anesthesiology, Vrije Universiteit University Medical Center, and 3 Department of Anesthesiology, Cardiothoracic Center, Amphia Hospital, Breda, Institute for Cardiovascular Research, Vrije Universiteit, 1081 BT Amsterdam, The Netherlands
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
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We studied the amplitude and response time (RT; time to 50% of maximal response) of pulmonary vasoreactivity and investigated whether the characteristics of pulmonary vasoreactivity could be modulated by endothelium removal, nitric oxide (NO) synthase inhibition [NG-nitro-L-arginine (L-NNA)], RhoA activation [lysophosphatidic acid (LPA)] and Rho kinase inhibition (Y-27632). Slow acetylcholine-induced pulmonary vasodilation (262 ± 5 s) was not due to the RT of endothelial NO release (45-55 s) and was always longer than RT in renal arteries (15 ± 4 s). The rate-determining step is located in the smooth muscle cells. This was confirmed by the existing differences between the RT of the NO solution and KCl-induced renal and pulmonary vasoreactivity in endothelium-denuded arteries. We found that the pulmonary contractile amplitude increases and the RT decreases by L-NNA or LPA. In contrast, Y-27632 reduced the contractile amplitude and increased the RT in pulmonary arteries. These phenomena were dependent on the contractile stimulus (phenylephrine or KCl). In conclusion, slow pulmonary vasoreactivity is a smooth muscle cell characteristic that can be enhanced by RhoA and NO or endothelium removal. These effects were counteracted by Rho kinase inhibition. We show a role for RhoA/Rho kinase and NO in the modulation of pulmonary vascular reactivity.
nitric oxide electrode; endothelium; amplitude of constriction; response time
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
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ISOLATED SYSTEMIC ARTERIES show large differences in the amplitude and speed of their responses to constrictors and dilators. These differences depend on the type and location of the vessel and differences in smooth muscle cell (SMC) characteristics (3, 9, 17, 18, 22). The characteristics of the vascular reactivity of pulmonary arteries, which form a special group in the circulation, are not well described in the literature.
The two objectives of the present study were therefore as follows: First, do pulmonary arteries exhibit similar magnitudes of contraction and response times to agonists as renal arteries? Renal arteries are, like pulmonary arteries, organ conduit arteries that are sensitive to similar agonists as pulmonary arteries. Second, if the magnitudes of contraction and response times are different, is it possible to modify these characteristics so that the renal and pulmonary vascular responses become similar?
With respect to the second objective, we investigated whether modification of the pulmonary vascular contractility and response time can be accomplished by changes in the sensitivity of the myosin light chain (MLC) for Ca2+. One of the ways in which the sensitivity of the contractile apparatus for Ca2+ can be modified is via changing the activity of MLC phosphatase.
Figure 1 shows the role of MLC
phosphatase in the regulation of SMC contraction. MLC phosphatase is
inactivated by Rho kinase, which is activated by a GTP-bound active
form of Rho (RhoA), thereby increasing the SMC Ca2+
sensitivity (6, 10). RhoA can be activated by the
bioactive lipid lysophosphatidic acid (LPA) and inhibited by nitric
oxide (NO) via a cGMP protein kinase, whereas Rho kinase can be
inhibited by Y-27632 (13, 16, 18). Thus LPA and NO
inhibition would both lead to increased RhoA activity and therefore
increased Ca2+ sensitivity, suggesting a similarity in
their effects. To answer the second aim of our study in more
detail, we therefore investigated whether RhoA activation or NO
inhibition induces similar changes in the characteristics of
pulmonary vascular reactivity and whether Rho kinase inhibition
accomplishes complementary effects.
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MATERIAL AND METHODS |
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TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Experimental animals. The Institutional Animal Care and Use Committee approved the experimental procedures, which conformed to the guidelines of Vrije Universiteit (Amsterdam, The Netherlands). Male Wistar rats (Harlan; Zeist, The Netherlands) were housed under standard conditions. Rats of 304 ± 11 g body wt (n = 41) were anesthetized with pentobarbital sodium (Nembutal, 60 mg/kg ip, Sanofi Sante BV; Maassluis, The Netherlands) and the lungs and/or left kidney were removed. Lungs or kidneys were pinned in a dissecting dish containing MOPS buffer (4°C, pH 7.4), which consisted of (in mM) 145 NaCl, 5 KCl, 2 CaCl2, 1 MgSO4, 1 NaH2PO4, 5 dextrose, 2 pyruvate (Sigma-Aldrich; Zwijndrecht, The Netherlands), 0.02 EDTA, and 3 MOPS (all components except for pyruvate were obtained from Merck; Darmstadt, Germany).
Preparation and diameter studies. For vessel diameter studies, one pair of arteries was dissected from either the lung (two first-order side branches of the main pulmonary artery) or the kidney (two first-order side branches of the renal artery). The renal and pulmonary arteries are functionally equal: they are both organ conduit arteries with a comparable diameter and can be stimulated with the same agonists. KCl-induced constriction and the effects of RhoA activity were studied in endothelium-denuded arteries. The endothelium was deliberately removed from the arterial lumen with a bolus of 1 ml air, and the adequacy of endothelium removal was checked with acetylcholine.
For diameter measurements, one isolated artery was mounted in a pressure myograph consisting of a vessel chamber (bath volume, 2.5 ml) containing two cannulas, a circular heating coil, and a thermistor. The vessel chamber was filled with MOPS buffer (37°C, pH 7.4). The proximal and distal end of the artery were mounted onto the cannulas and secured with nylon sutures. Cannulas were chosen to fit vessel size. The proximal cannula was connected to a column filled with MOPS buffer, and the distal cannula was closed, i.e., there was no luminal flow. The applied transmural pressure was set at values appropriate for the two vessel types, 15 and 80 mmHg in pulmonary and renal arteries, respectively. Agonists were added to the buffer solution, which was superfused over the arteries by using a pump (pump flow rate, 50 ml/h, Perfusor Secura B; Braun, Germany). Diameter changes were recorded with a video micrometer system camera (Sony Hyper Had SSC-DC38P; Breda, The Netherlands) mounted on a microscope (Zeiss Stereomicroscope SV-6; Weesp, The Netherlands). The video camera was connected to an electronic measurement system to monitor the vessel diameter continuously.NO measurements. For NO measurements, the second artery was cut open longitudinally and pinned on a silicon layer in a second organ bath. This organ bath was also filled with MOPS buffer, and agonists were added to the buffer and mixed. NO measurements were performed on the endothelial cell layer of the artery (21).
The electrochemical monitoring of NO was performed using a three-electrode system consisting of a NO microsensor, reference electrode, and counter electrode (sensitivity ±1 nM/pA). The NO microsensor was produced by threading a single carbon fiber (Ten Cate Advanced Composites; Amsterdam, The Netherlands) through a pulled end of a glass capillary, with a 2-mm length protruding according to a procedure previously described (12). The carbon fiber was coated with a polymeric layer of nickel (II) tetrakis (3-methoxy-4-hydroxyphenyl) porphyrin (Interchim; Montluçon, France) and two 1.25% Nafion layers (Sigma-Aldrich). Potential differences were expressed between the coated fiber and the reference electrode (Ag-AgCl electrode). A platinum wire was used as counter electrode. The Electrochemical Microprobe System 100 (EMS-100, Biologic; Claix, France) was used for the differential normal pulsed amperometry. The oxidation potential for NO was determined from a voltammogram and was set to 680 mV during all amperometric experiments. With the use of a potential difference of 680 mV, the porphyrinic microsensor was free of interference from all reagents used in these experiments. The sensitivity of each electrode (response time ~10 ms) was determined by calibration of the electrode after every experiment using aliquots of the NO solution. Aliquots of NO solution were prepared by serial dilutions of the saturated NO solution. To produce a saturated NO solution, deionized water was bubbled with pure argon (AGA Gas BV; Amsterdam, The Netherlands) for 20 min. This deoxygenated water was then bubbled with pure NO gas (AGA Gas BV) for 20 min and kept under a NO atmosphere until use. The saturated solution was diluted with deoxygenated water. The slope of the linear relation between the measured current (in pA) and the applied NO concentration (in nM) determined the sensitivity of the electrode.Protocol. When an agonist was applied to the cannulated artery, the speed of the superfusion pump was increased transiently up to 1 ml/s (bath volume, 2.5 ml) to quickly replace the volume of buffer in the organ bath.
For the first objective, we studied the amplitude and the response time of the diameter changes and NO release for acetylcholine, NO solution, and KCl. The response time was defined as the time interval to reach 50% of the maximal diameter change (RT0.5,Ø) or the maximal NO release (RT0.5,NO). First, the amplitude and response times of the acetylcholine-induced NO release and vasodilation were studied in pulmonary and renal arteries. Arteries were constricted with l-phenylephrine hydrochloride (3 × 10
7 and 106 M phenylephrine in pulmonary
and renal arteries, respectively, Sigma-Aldrich). NO release and
vasodilation were studied in both artery types with increasing
concentrations of acetylcholine, starting with 3 × 108 M until maximal vasodilation was induced (3 × 108-105 M, Sigma-Aldrich). The
concentration of acetylcholine inducing maximal vasodilation was
determined in separate experiments to avoid desensitization due to high
concentrations of acetylcholine (106 M in renal and
105 M in pulmonary arteries, respectively). To check
whether acetylcholine-induced vasodilation is completely NO mediated,
NO release and diameter changes to 105 and
106 M acetylcholine (pulmonary and renal arteries,
respectively) were also recorded after incubation of the vessels for 30 min with the NO synthase inhibitor
NG-nitro-L-arginine
(L-NNA; 104 M, Bachem; Bubendorf, Germany).
To study endothelium-independent vasodilation, subsequent
concentrations of the NO solution were applied to endothelium-denuded pulmonary and renal arteries (3 × 109-3 × 107 M). NO solution was prepared as similar as the
saturated NO solution used for the calibration of the NO electrodes.
Furthermore, the amplitude and RT0.5,Ø of KCl-induced
constriction were compared in pulmonary and renal arteries that were
both endothelium denuded. The high-KCl buffer consisted of (in mM) 90 NaCl, 60 KCl, 2 CaCl2, 1 MgSO4, 1 NaH2PO4, 5 dextrose, 2 pyruvate
(Sigma-Aldrich), 0.02 EDTA, and 3 MOPS (all components except for
pyruvate were obtained from Merck).
For the second objective, the amplitude and RT0.5,Ø of
phenylephrine- or KCl-induced constriction in intact and
endothelium-denuded pulmonary arteries were studied under control
conditions and after incubation with the RhoA activator LPA
(105 M, Sigma-Aldrich), the Rho kinase inhibitor Y-27632
(3 × 107 M, Tocris Cookson; Bristol, UK), and
L-NNA (104 M). The effects of LPA and Y-27632
were studied in a random order in the same artery, which was exposed
three times to phenylephrine or KCl. Papaverine (104 M,
Sigma-Aldrich) was added to the superfusate to determine the maximal diameter.
Statistics and calculations. In all experiments, papaverine-induced vasodilation was used to determine the maximal passive diameters of pulmonary and renal arteries. Constrictor responses are expressed as the percent constriction from the maximal diameter. Vasodilatory changes are shown as the percent dilation during phenylephrine-induced constriction. For acetylcholine-induced NO measurements, the steady-state level of the NO response was taken as the measured concentration. Data are given in means ± SE. Statistical analysis was done by ANOVA and Bonferroni post hoc tests and paired or unpaired t-tests. Differences were considered statistically significant at P < 0.05.
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Amplitude and response time of pulmonary and renal vasodilation.
Starting diameters equaled maximal diameters obtained with papaverine
and were 810 ± 27 and 1,178 ± 16 µm for renal and
pulmonary arteries, respectively. Both pulmonary and renal arteries
developed <5% spontaneous tone. Phenylephrine (3 × 107 and 106 M) induced 29.1 ± 0.8%
and 20.4 ± 1.8% constriction in renal (n = 6)
and pulmonary (n = 6) arteries, respectively. In
phenylephrine-constricted arteries, a concentration-dependent
acetylcholine-induced NO release and diameter change were measured
(Fig. 2). Although 106 M
acetylcholine induced more NO release in renal arteries (181 ± 75 nM) compared with pulmonary arteries (65 ± 10 nM), maximal NO
release in both renal and pulmonary arteries was equal (175 ± 13 and 181 ± 75 nM for pulmonary and renal arteries, respectively). The highest acetylcholine-induced NO release also resulted in the
largest diameter change (for 106 and 105 M
of acetylcholine in renal and pulmonary arteries, respectively). After
incubation with L-NNA, the acetylcholine-induced NO release was abolished in both vessel types (in renal and pulmonary arteries, P = 0.009 and P = 0.003, respectively;
highest concentration acetylcholine vs. L-NNA,
n = 6).
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7 M acetylcholine
in renal arteries made determination of the RT0.5,Ø unreliable, these data are not presented in Fig. 3. The
RT0.5,Ø was ~240 s for the pulmonary arteries and ~15
s for the renal arteries (P < 0.001, pulmonary vs.
renal). In pulmonary arteries, the 105 M
acetylcholine-induced RT0.5,NO was 55 ± 5 s and
the RT0.5,Ø was 253 ± 5 s. In renal arteries,
we found a 106 M acetylcholine-induced
RT0.5,NO of 45 ± 9 s and a RT0.5,Ø of 15 ± 4 s, i.e., here the diameter response time is faster
than the NO release.
Vascular reactivity characteristics in endothelium-denuded
arteries.
The slow pulmonary vascular reactivity, independent of the response
time of NO release, suggests that the diameter response time is
determined by smooth muscle cell characteristics. To study this in more
depth, renal and pulmonary arteries were endothelium denuded to study
NO solution-induced vasodilation in SMCs only (Fig.
4). NO solution induced a
concentration-dependent vasodilation in both pulmonary and renal
arteries that was slightly larger in renal than in pulmonary arteries
(Fig. 4A). However, the RT0.5,Ø of NO
solution-induced vasodilation was larger in pulmonary arteries than in
renal arteries (Fig. 4B). The RT0.5,Ø of 3 × 107 M NO solution was 62.5 ± 14.3 s in
pulmonary arteries (n = 6) and 16.0 ± 8.7 s
in renal arteries (n = 6, P = 0.01). In
general, NO solution-induced vasodilation was faster than
acetylcholine-induced vasodilation in pulmonary arteries but not in
renal arteries (Figs. 3 and 4).
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Characteristics of pulmonary arteries can approach those of renal
arteries after NO synthase inhibition.
In the second part of the study, we investigated whether slow pulmonary
vascular reactivity can be modified such that the characteristics of
pulmonary vascular reactivity resemble those of renal vasoreactivity.
The 
1-adrenergic vasoconstrictor phenylephrine was used
to study receptor-mediated constriction, whereas receptor-independent constriction was studied with KCl. Figure
6 represents the phenylephrine- or
KCl-induced vasoconstriction in control arteries, endothelium-denuded arteries, and arteries that were incubated with L-NNA.
Phenylephrine (3 × 107 M) induced a
vasoconstriction of 19.1 ± 1.7% in control arteries (Fig.
6A). The magnitude of constriction was increased by
endothelium removal (28.8 ± 1.7%, P = 0.01 vs.
control) or incubation with L-NNA (32.8 ± 2.2%,
P = 0.03 vs. control, n = 7).
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Modulation of RhoA or Rho kinase changes the response time of
pulmonary arteries.
Figure 7 represents the effects of LPA
and Y-27632 on pulmonary vascular reactivity in endothelium-denuded
arteries. Figure 7A shows the effects of RhoA and Rho kinase
activity changes on the magnitude of phenylephrine-induced
constriction. LPA did not increase the amplitude of constriction, but
application of Y-27632 decreased the level of constriction (8.8 ± 1.6%) compared with control arteries (28.8 ± 1.7%,
P = 0.001). The magnitude of the KCl-induced
contractile response was not affected by LPA or Y-27632 (Fig.
7B).
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
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We found that the acetylcholine-induced diameter response time of pulmonary arteries is longer than that of renal arteries. Slow acetylcholine-induced pulmonary vasodilation is not due to the response time of endothelial NO release, and the rate-determining step is located in SMCs. The latter was confirmed by the existing differences between the RT0.5,Ø of NO solution-induced renal and pulmonary vasodilation in endothelium-denuded arteries. In addition, in renal arteries, the amplitude of KCl-induced vasoconstriction was higher with a lower response time than in pulmonary arteries.
Furthermore, we found that the amplitude of pulmonary artery constriction can be increased and the response time can be reduced by NO synthase inhibition or RhoA activation. In contrast, Rho kinase inhibition decreased the diameter amplitude and increased the response time of pulmonary arteries. We found that the RhoA pathway plays a major role in receptor-mediated constriction and less in constriction induced by direct depolarization of SMCs.
Acetylcholine-induced vasodilation in pulmonary and renal arteries. Our study describes acetylcholine-induced concentration-dependent NO release in pulmonary and renal arteries. In contrast, the acetylcholine-induced RT0.5,NO was not dependent on the applied concentration of acetylcholine and was similar in both vessel types. The response time of the NO microsensor is sufficiently short (10 ms) to interfere with these results. An increased concentration of acetylcholine induces more endothelial Ca2+ influx and therefore activates more endothelial NO synthase (NO synthase III) molecules, resulting in an increased NO release (8). However, our results suggest that the quantity of NO synthesized by NO synthase III per unit time is independent of the acetylcholine concentration in both vessel types.
The RT0.5,Ø of acetylcholine-induced renal vasodilation is four times lower than the acetylcholine-induced RT0.5,NO. There is evidence that endothelial NO release activates the cyclooxygenase enzyme pathway, resulting in a fast coproduction of vasodilating prostaglandins (4, 15). A fast prostacyclin release could induce a shorter RT0.5,Ø than NO does. However, pilot studies showed that inhibition of cyclooxygenase did not affect the renal vascular reactivity. The mediator endothelium-derived hyperpolarization factor can be excluded as well, because L-NNA completely inhibited acetylcholine-induced vasodilation in renal arteries.Slow pulmonary vascular reactivity is a SMC characteristic. NO solution was applied in endothelium-denuded renal and pulmonary arteries to prove the SMC dependency of slow pulmonary vasodilation. The amplitude of NO-induced vasodilation was similar in renal and pulmonary arteries, but the RT0.5,Ø was longer in pulmonary than in renal arteries. The amplitude and RT0.5,Ø of KCl-induced vasoconstriction differed as well between endothelium-denuded renal and pulmonary arteries. Both findings indeed confirm that the characteristics of the SMCs determine slow pulmonary vascular reactivity, as was seen for acetylcholine-induced dilation.
Effects of endothelium removal and NO synthase inhibition on pulmonary vascular reactivity. We subsequently investigated whether it is possible to modify pulmonary SMC characteristics via changing the MLC phosphatase activity. We used receptor-mediated and receptor-independent vasoconstrictors that act via different mechanisms. Phenylephrine activates phospholipase C and modulates the SMC Ca2+ concentration via the influx of Ca2+ and the release of Ca2+ from the sarcoplasmic reticulum (1, 11). In contrast, KCl-induced constriction acts mainly via direct depolarization of the SMC, resulting in Ca2+ influx via voltage-operated Ca2+ channels.
The amplitude of phenylephrine-induced vasoconstriction but not of KCl-induced vasoconstriction was increased after endothelium removal and NO inhibition. Pulmonary arteries maintain their low vascular resistance partly by the release of NO (14). Furthermore, it has been reported by our group (5) that phenylephrine induces NO release. The combination of basal and phenylephrine-induced NO release reduces the amplitude of phenylephrine-induced constriction. With the use of L-NNA, NO release is reduced and more constriction ensured via direct effects of cGMP on the SMC Ca2+ concentration or via an effect on the RhoA activity, concluding that the phenylephrine-induced constriction is an accumulation of vasoconstrictor and vasodilator effects. This suggests a role for endothelial NO release as a modulator of specific contractile responses in the pulmonary vasculature. Although KCl might induce NO release as well via SMC Ca2+ influx via gap junctions, we found no effect of endothelium removal or NO synthase inhibition on the magnitude of KCl-induced constriction. These results suggest that the type of constriction also determines the characteristics of pulmonary vascular reactivity. Both endothelium removal and L-NNA treatment diminished the response times of phenylephrine- and KCl-induced vasoconstriction. Remarkably, we were able to reduce the response time of the pulmonary contractile responses such that they were almost identical to those of the renal arteries. NO might be, like Y-27632, an inhibitor of the Rho pathway and stimulate vasodilation. Removal of NO from the vasculature might result in RhoA activation and therefore an increased contractile amplitude and faster constriction. Furthermore, our results for KCl suggest that the first minutes in which the KCl-induced constriction develops, NO still diminishes the speed at which depolarization induces a SMC Ca2+ increase. Inhibition of NO will therefore result in an increased speed of constriction but also in an unaltered amplitude. These findings also suggest a more important effect of NO on the SMC Ca2+ concentration than on the Ca2+ sensitivity. For all experiments in pulmonary arteries, the RT0.5,Ø of phenylephrine-induced constriction was lower than the RT0.5,Ø of KCl-induced constriction. The pathway of Ca2+ increase via influx or the sarcoplasmic reticulum in combination with Ca2+ sensitivity is probably a faster process than depolarization-induced Ca2+ influx. The KCl-induced intracellular Ca2+ increase probably inhibits the sarcolemmal Ca2+ influx, thereby resulting in a slower contractile response compared with phenylephrine. For KCl-induced constriction, renal arteries were faster than pulmonary arteries. This difference is not due to a variance in the L-type voltage-operated Ca2+ channels or Ca2+ influx characteristics of both vessel types (2).RhoA/Rho kinase are involved in the modulation of pulmonary vascular reactivity. The amplitudes of both phenylephrine- and KCl-induced constriction were not affected by LPA in endothelium-denuded pulmonary arteries. Others (19, 20) have confirmed these results for KCl but found a LPA-induced augmentation of the amplitude when constriction was induced by receptor-dependent agonists. However, in those studies, phenylephrine was not included. The absence of an LPA-induced augmentation of the amplitude of constriction suggests that RhoA activity cannot be enhanced in these arteries or that the arteries were maximally constricted. In contrast, Rho kinase inhibition decreased the amplitude of the phenylephrine response but not of KCl-induced constriction. This suggests that the Rho pathway is only involved in pharmacomechanical constriction. Our results suggest that the level of RhoA activity in SMCs determines the characteristics of vasoconstriction.
Although LPA did not affect the level of constriction, the response times of phenylephrine-induced contraction were decreased by LPA. The mechanism underlying this effect of LPA probably involves a LPA-induced increase of the Ca2+ sensitivity of the contractile apparatus, resulting in faster myosin-actin coupling. The response time of the Ca2+ influx cannot account for the attenuation of the RT0.5,Ø of phenylephrine-induced constriction, because phenylephrine induces a maximal pulmonary SMC Ca2+ increase within 10 s (7). LPA affected only the response times of phenylephrine-induced constriction in intact but not in endothelium-denuded pulmonary arteries. Removal of NO probably decreased the response time of phenylephrine-induced vasoconstriction so that LPA did not enlarge this phenomenon. LPA did not affect the response times of KCl-induced constriction, suggesting that the response time was already optimal or that KCl-induced constriction is not mediated via Rho kinase. However, application of the Rho kinase inhibitor Y-27632 significantly increased the response times of both contractile stimuli in endothelium-denuded arteries. We conclude that the level of RhoA activity affects the amplitude and response time of vasoconstriction. We conclude that the RT0.5,Ø of pulmonary vasodilation and vasoconstriction is determined by SMCs and is in all cases longer than the RT0.5,Ø of renal SMCs. NO inhibition enhanced the characteristics of pulmonary vasoconstriction so that they resembled those of renal arteries. We were able to show opposite effects of LPA and Y-27632 on pulmonary constriction characteristics. Finally, a decreased NO synthase or an increased RhoA activity might play a role in a disturbed pulmonary vascular responsiveness and might therefore contribute to the induction of pathophysiological processes.| |
ACKNOWLEDGEMENTS |
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This study was supported by AGA Linde Healthcare, The Netherlands.
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FOOTNOTES |
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Address for reprint requests and other correspondence: C. Boer, Laboratory for Physiology, Institute for Cardiovascular Research Vrije Universiteit, VU Univ. Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands (E-mail: c.boer.physiol{at}med.vu.nl).
10.1152/ajpheart.00093.2001
Received 9 February 2001; accepted in final form 1 November 2001.
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TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
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EC) and
L-NNA treatment on the amplitude of PE- and KCl-induced
constriction in pulmonary arteries. Endothelium removal and
L-NNA treatment attenuated only the amplitude of PE-induced
constriction. Endothelium removal and L-NNA treatment
decreased the response times of both PE (C) and KCl
(D). *P < 0.05 vs. control.
