Laboratoire de Physiopathologie de la Paroi Artérielle, Faculté de Médecine, 37032 Tours, France
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ABSTRACT |
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Exogenous
carbon monoxide (CO) can induce pulmonary vasodilation by acting
directly on pulmonary artery (PA) smooth muscle cells. We investigated
the contribution of K+ channels to the regulation of
resistance PA resting membrane potential on control (PAC) rats and rats
exposed to CO for 3 wk at 530 parts/million, labeled as PACO rats.
Whole cell patch-clamp experiments revealed that the resting membrane
potential of PACO cells was more negative than that of PAC cells. This
was associated with a decrease of membrane resistance in PACO cells.
Additional analysis showed that outward current density in PACO cells
was higher (50% at +60 mV) than in PAC cells. This was linked to an increase of iberiotoxin (IbTx)-sensitive current. Chronic CO
hyperpolarized membrane of pressurized PA from 46.9 ± 1.2 to
56.4 ± 2.6 mV. Additionally, IbTx significantly depolarized
membrane of smooth muscle cells from PACO arteries but not from PAC
arteries. The present study provides initial evidence of an increase of
Ca2+-activated K+ current in smooth muscle
cells from PA of rats exposed to chronic CO.
Kv; K channel blockers; 4-aminopyridine; pressurized artery; iberiotoxin
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INTRODUCTION |
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THE RELATIONSHIP BETWEEN
MEMBRANE POTENTIAL (Em) and tension in
arterial smooth muscles has been well studied. It is accepted that
tension in smooth muscle cells is, in part, regulated by the
availability of Ca2+ in the cytosol, which depends in part
on the activity of K+ channels that control resting
Em. Pulmonary arterial (PA) smooth muscle cells
have a high input resistance in the resting state [found to be 18 G
by Evans et al. (13) and 4.7 G
by Park et al.
(29)] that corresponds to very low ionic channel activity near resting Em. The consequence is that opening
or closure of very few channels can cause a substantial change in
Em resulting in modification of arterial
tone. On the other hand, PA smooth muscle cells have a high
density of Ca2+-activated K+ (KCa) channels and
voltage-activated K+ (Kv) channels. Both of these channels
regulate resting Em of PA smooth muscle cells
(3, 27, 37), and KCa is suspected to act as a feedback
mechanism in regulation of Ca2+ entry (6);
thus they are important in regulating PA tone (32). Carbon
monoxide (CO) is an endogenously generated gas as well as a ubiquitous
environmental pollutant. The two major sources of exogenous CO exposure
are automotive emissions and cigarette smoke. Concentrations of CO
found in urban environments have been correlated with hospital
admissions, mortality, and morbidity caused by cardiovascular and
pulmonary diseases (19, 24, 31, 41). Average CO
concentrations have been found to be 1-9 parts per million (ppm),
but there are many conditions in which exposures exceed these levels.
Indeed, cigarette smoke contains CO levels ranging from 35 to 1,000 ppm
(38), and exposure to high levels of CO can occur in
numerous occupational settings, such as those experienced by tunnels
workers (9). CO is also an endogenously generated gas that
regulates vascular tone (39). The predominant biological
source of CO is from degradation of heme by heme oxygenase (HO)
(36). At least two isoforms of HO, HO-1 and HO-2, an
inducible and a constitutive isoform, respectively, have been
identified and are present in vascular smooth muscle cells
(12). Most experiments suggest that endogenously generated
CO affects vascular tone in physiological and pathological conditions,
but these experiments were performed using an activator/blocker of HO
to activate or inhibit the endogenous CO production
(39). In PA smooth muscle cells, HO-1 is
transiently increased by chronic hypoxia (7) whenever
sustained activation prevents the development of hypoxic pulmonary
hypertension (8). Nevertheless, there is no direct evidence that this last effect is due to CO, and an effect of chronic
exogenous CO on pulmonary tone is lacking. However, several lines of
investigation provide evidence that acute CO is a vasodilator acting
directly on vascular smooth muscle cells (39) that also inhibits smooth muscle cell proliferation (23). In the
pulmonary circulation, exogenous CO decreases vascular resistance
(11) and inhibits hypoxic pulmonary vasoconstriction
(34), probably by a direct vasorelaxing effect of CO on
smooth muscle cells (33). The mechanism of CO-induced PA
relaxation is not known, but it could act by activating K+
channels. Indeed, acute exposure to CO has been shown to activate KCa
and Kv channels, respectively, in tail artery smooth muscle cells of
rats (40) and in jujenal circular smooth muscle cells of
humans (14). Nevertheless, the physiological and chronic importance of endogenous CO on K+ channel functions was not
directly studied. Indeed, only studies using blockers of HO to inhibit
the endogenous CO production and then the changes in K+
channel function have been performed (18, 21, 43).
It has been suggested that drug therapies acting on K+ channel expression may have potential value for the treatment of vascular diseases (5). Because acute CO activates KCa channels and because these channels have been shown to be compensatory vasodilatory pathways in systemic hypertension (22), we speculated that chronic CO could activate these channels, which would explain, in part, the vasodilatory effect of CO in the pulmonary circulation.
In this study we examined for the first time the effect of chronic exogenous CO exposure on the regulation of resting Em of pressurized resistance PA. Then we examined passive membrane properties and K+ channel blocker-sensitive currents of resistance PA smooth muscle cells. The present study provides initial evidence of an increase of IbTx-sensitive K+ current that hyperpolarizes resistance PA smooth muscle cells of rats exposed to chronic CO. A preliminary report of part of this study has been published in abstract form (10).
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MATERIALS AND METHODS |
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Exposure to CO. All animal experiments were conducted according to the ethical standards of the Ministère Français de l'Agriculture for animal care and use. Exposure to CO was performed using methods previously described (4). Adult female Wistar rats (250 g) were placed in an exposure chamber inflated by an air-CO mixture for 3 wk at 530 ppm at 24°C (labeled as PACO). The sudden death of rats was avoided by gradually raising the CO concentration from 300 ppm on the first day to 400 ppm on the second day and 530 ppm on the third day. Another group of rats, the control group, was placed in the same chamber but without CO (labeled as PAC). During experiments, CO concentration in the exposure chamber was continuously monitored (Analyzer Surveyor S). The CO chamber was opened twice a week for <5 min for changing cages and replenishing them with food and water. Mean PA pressure was not significantly different between PAC and PACO rats (12.7 ± 1.2 vs. 13.3 ± 3.0 mmHg, N = 3).
Tissue preparation for microelectrode recording. Animals were deeply anesthetized with pentobarbital sodium (60 mg/kg ip). The thorax was opened, and lungs were rapidly excised and immersed in cold (4°C) physiological saline solution (PSS). In the left pulmonary lobe, an intrapulmonary resistance artery with an internal diameter of <150 µm was isolated and gently cleaned of parenchyma and adhering connective tissue under a dissection microscope. Collateral arterioles of the resistance artery were tied with 30-µm-thin silk to make surgical sutures. We removed the endothelium by passing an air bubble inside the artery.
PSS solution contained (in mM): 138.6 NaCl, 5.4 KCl, 1.8 CaCl2, 1.2 MgCl2, 0.33 NaH2PO4, 10 HEPES, and 11 glucose. pH was adjusted to 7.4 using NaOH.Recording of Em on pressurized resistance arteries. A freshly prepared resistance artery was transferred in a 2.5-ml organ chamber hold at 37°C and filled with PSS. One end of the artery was mounted on a glass micropipette (Clark Electromedical Instrument) connected to a pressure captor (Baxter) and to a pressure controller (Hewlett Packard). The other end of the artery was mounted on a micropipette connected to a stopcock. The organ chamber was placed on the stage of a microscope (Olympus) fitted with a video camera (Sanyo) leading to a monitor (Sony). PSS at 37°C was used for both continuously superfusing (5 ml/min) and perfusing arteries. After 10 min of perfusion, the stopcock was closed and the intraluminal pressure was slowly increased to 14 mmHg. This level of pressure was maintained during a 60-min equilibration period before experiments.
Em of arterial smooth muscle cells was recorded using glass microelectrodes (Clark Electromedical Instrument) filled with 3 M KCl solution and connected to a microelectrode amplifier (Biologic VF 180). The entire set-up was mounted on an antivibration system (TMC Micro-g), and manipulation was performed using a micromanipulator (Narishige). Response for K+ channel blockers was recorded after adding aliquots of 4-aminopyridine (4-AP) for a final concentration of 3 mM in the chamber or iberiotoxin (IbTx, 100 nM) to block Kv channel type and KCa channel type, respectively. We added these drugs directly to the vessel chamber after stopping the superfusion.Isolation of smooth muscle cells. Enzymatic isolation of single vascular smooth muscle cells was performed according to published methods of dissociation for rat microvessels (17). Briefly, intrapulmonary resistance arteries with internal diameters of <100 µm were placed in dissociation solution (Ca2+ free) for 10 min at room temperature. Tissue was then placed in dissociation solution at 37°C containing 1 mg/ml of papain (Sigma) and 1 mg/ml of dithioerythritol for 18 min. The vessel was then put in a dissociation solution at 37°C containing 1.6 mg/ml collagenase (type H, Sigma), 1.6 mg/ml trypsin inhibitor (type 1-S, Sigma), and 0.25 mg/ml elastase (type IV, Sigma) for 8 min. The tissue was then put in dissociation solution (free of enzymes) for 5 min and then gently agitated with a polished wide-bore Pasteur pipette to release the cells. Cells were stored at 4°C and used between 2 and 8 h after isolation. Only long, smooth, optically refractive cells were used for patch-clamp measurements.
Dissociation solution contained (in mM): 145 NaCl, 4 KCl, 1 MgCl2, 10 HEPES, and 10 glucose. pH was adjusted to 7.3 using NaOH.Electrophysiology.
Electrophysiological recording was obtained using the conventional
patch-clamp of Hamill et al. (16). The cells were placed in a 0.5-ml-volume bath containing PSS (see Tissue preparation for microelectrode recording) and were continuously perfused by gravity at the rate of 1 ml/min. Different test solutions were applied
to the cell at 100 µl/min by microcapillaries. Cell membrane currents
were recorded with an Axopatch 200B patch-clamp amplifier (Axon
Instruments). Patch pipettes were pulled from borosilicate glass
capillaries and had resistances of 4-7 M. The head-stage ground
was connected to an Ag-AgCl pellet that was placed in a side bath
filled with the pipette solution and connected to the main bath via an
agar bridge containing 3 M KCl. We cancelled the junction potentials
between the electrode and the bath by using the voltage pipette offset
control of the amplifier. The capacitance of the pipette was cancelled.
Chemicals. Stock solutions of 4-AP and IbTx were prepared in distilled water and then diluted in PSS at an appropriate concentration. 4-AP solution was dissolved as stock solution buffered to pH 7.4 with HCl. All chemicals were from Sigma (St. Quentin Fallavier, France).
Statistics. Results are expressed as means ± SE. Statistical analysis was made with the unpaired Student's t-test or the Mann-Whitney's test when normality test failed (Anderson-Darling test). For comparison between more than two means we used analysis of variance (ANOVA) followed by Dunnett's test or Mood's median test when normality test failed. The number of experiments (n) refers to the number of cells and N to the number of animals. Differences were considered significant when P < 0.05. Statistical analysis was realized using Minitab software (Minitab).
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RESULTS |
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Effect of CO on resting Em of smooth muscle cells from
pressurized resistance PA smooth muscle cells.
As shown in Fig. 1A, IbTx had
no effect on resting Em of PAC arteries, whereas
4-AP depolarized the membrane. Figure 1B shows no
significant difference between resting Em
recorded before and after IbTx (n = 19, N = 3), whereas 4-AP (n = 9, N = 3) significantly depolarized the membrane
(P < 0.001, post hoc unpaired t-test).
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Passive membrane properties of PAC and PACO cells.
Using 10-mV voltage steps, we calculated Cm, and
no statistically significant difference (P > 0.05, unpaired t-test) was observed between mean values (Fig.
3A, left) of cells
isolated from 12 PAC (n = 18) rats and those of 7 PACO
rats (n = 18). Using current-clamp experiments, we
measured the resting Em of PAC cells
(n = 18, N = 19), which average
37.8 ± 5.1 mV (Fig. 3A, middle). This value is in the range of resting Em already
reported in this preparation. Nevertheless, a more hyperpolarized
membrane was obtained in PACO cells (
45, 6 ± 4.7 mV,
n = 18, N = 7) compared with PAC cells (P < 0.05, unpaired t-test). In the same
way, the Rm, which was estimated as the slope of
the current-voltage relationship curves between
80 mV and
60 mV,
was significantly smaller (P < 0.05, unpaired
t-test) in PACO (n = 18, N = 7) cells compared with PAC cells (n = 18, N = 12) (Fig. 3A, right). As we
determined that Cm was not different in cells
isolated from the two populations of rats, this was not predictive of
the recorded increase of the net outward current density (Fig.
3B). The average current density of net outward current at
+60 mV in PACO cells represented a 1.7-fold increase compared with PAC
cells. Indeed, in PACO cells the average current density was 49.5 ± 8.5 pA/pF (n = 18, N = 7) and was
significantly higher than in PAC cells (n = 18, N = 12), in which it was 29.3 ± 3.4 pA/pF
(P < 0.05, ANOVA and post hoc unpaired
t-test).
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Effect of chronic CO on net whole cell current.
The effect of chronic CO on whole cell current from a typical
experiment is shown in Fig.
4A. The cell
Em was held at 80 mV and stepped in 10-mV
increments from
80 mV to +60 mV for 400 ms, returning to
80 mV
between steps. The outward current was recorded in a 10-pF PAC cell
(Fig. 4A, left) and in a 9.5-pF PACO cell (Fig.
4A, right). In this example, the cell isolated
from the chronic CO-treated rats showed a much larger net outward
current. To take into account the cell membrane area, we divided each
current amplitude by the respective Cm. Figure
4B shows the mean current density-voltage relationship in 18 PAC cells from 12 animals and 18 PACO cells from 7 animals. The current
density in PACO cells was markedly and significantly higher
(P < 0.05, ANOVA) than in cells isolated from PAC
animals (49.5 ± 8.5 pA/pF and 29.3 ± 3.4 pA/pF at +60 mV,
respectively). Over the range of potentials where the currents
obviously activated (i.e.,
40 to
50 mV), chronic CO tended to
increase outward current (Fig. 4B, inset).
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Effect of K+ channel blockers on
CO-increased current.
The nature of the current activated by chronic CO was further examined
with specific K+ channel blockers. Previous studies have
described three major K+ channels in PA smooth muscle
cells, an IbTx-sensitive KCa channel (30) and two
4-AP-sensitive Kv channels (27, 28). Outward currents
recorded in a 9.5-pF cell isolated from PAC rat (Fig. 3A)
exhibited little sensibility to superfusion with 100 nM IbTx, whereas a
subsequent addition of 3 mM 4-AP in the superfusion solution containing
100 nM IbTx blocked a larger component of the current. The mean current
density-voltage relationship (Fig. 5B) confirmed the
nonsignificant effect (P > 0.05, ANOVA and Dunnett's post hoc test) of 100 nM IbTx on PAC cells (n = 7, N = 6) for all voltages tested. In comparison, 3 mM
4-AP significantly decreased the current (P < 0.05, ANOVA and Dunnett's post hoc test, n = 6, N = 5). In contrast to PAC cells, a large component of
outward current recorded in cells isolated from PACO rat (6.4 pF) was blocked by 100 nM IbTx (Fig.
6A). Subsequent addition of 3 mM 4-AP in the superfusion solution containing 100 nM IbTx reduced the
residual outward current like in PAC cells. The mean current density-voltage relationship confirmed the large effect of IbTx on PACO
cells (Fig. 6B). Indeed, in six PACO cells isolated
from three animals, the effect of IbTx was significant
(P < 0.05, ANOVA and Dunnett's post hoc test).
Furthermore, over the range of potentials where the currents obviously
activated (i.e., 40 to
50 mV), IbTx decreased the outward current,
and the resting Em (estimated to the
Em where the current density was 0 pA/pF) was
shifted to more positive values (Fig. 6B, inset).
(Note that this effect was not significant in PAC cells; Fig.
5B, inset.) 4-AP still significantly decreased
(P < 0.05, ANOVA and Dunnett's post hoc test) outward
current in PACO cells (n = 6, N = 3).
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Effect of chronic CO on IbTx- and 4-AP-sensitive currents.
The magnitude of IbTx-sensitive current can be obtained by subtracting
the net outward current observed in normal PSS solution from the
outward current recorded in the presence of 100 nM IbTx, thereby
obtaining the IbTx-sensitive current. In Fig.
7A, the current
density-voltage relationship for this difference is shown. Compared
with PAC cells (n = 7, N = 6), this
IbTx-sensitive current was significantly increased (P < 0.05, Mood's median test) in PACO cells (n = 6, N = 3). At +60 mV, this current represented ~44%
(17.5 ± 7.5 pA/pF) of net outward current in PACO cells and ~9% (2.8 ± 0 .5 pA/pF) in PAC cells. We showed that subsequent addition of 4-AP in the bath induced an additional decrease of the
outward current in both type of cells. The magnitude of the outward
current inhibited by 3 mM 4-AP was obtained by subtracting the outward
current observed in the presence of IbTx solution from the outward
current recorded in the presence of 100 nM IbTx plus 3 mM 4-AP. The
current density-voltage relationship for this 4-AP-sensitive current is
shown in Fig. 7B, and we observed no significant difference
(P > 0.05, Mood's median test) between PAC and PACO
cells. For example, the 4-AP-sensitive current at +60 mV represented
~55% of net current (13.7 ± 2.2 pA/pF) in PAC cells
(n = 6, N = 5). This is not different
from the 4-AP-sensitive current observed in PACO cells (14.4 ± 3.6 pA/pF, n = 6, N = 3) but
represented ~38% of net current. Furthermore, although the 4-AP- and
IbTx-sensitive currents are significantly different in PAC, these
currents are not different in PACO cells.
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DISCUSSION |
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This study demonstrates that an IbTx-sensitive K+ current was activated in resistance PA smooth muscle cells of rats exposed for 3 wk to CO. This could explain the hyperpolarization and the modification of Em reactivity to K+ channel blockers in resistance PA cells from PACO rats.
Pharmacological relevance of 530-ppm chronic CO inhalation. CO is an endogenously generated gas as well as an ubiquitous environmental gas. The two major sources of exogenous CO exposure are automotive emissions and cigarette smoke. Indeed, cigarette smoke, a frequently cited source of indoor CO, contains CO levels ranging from 35 to 1,000 ppm (38). In addition, exposure to high levels of CO can occur in numerous occupational settings, such as those experienced by tunnel workers (9). Not surprisingly then, hospital admissions, mortality, and morbidity are correlated with CO levels in air (19, 24). Effects of exogenous CO result primarily from its competition with oxygen binding to hemoglobin; nevertheless, a direct action of CO has also been demonstrated on vascular smooth muscles (39).
Chronic CO-induced modifications of passive membrane properties of
resistance PA cells.
Results from the present investigation demonstrate that chronic CO
hyperpolarized the membrane and caused an increase of IbTx-sensitive outward current without changing the Cm of the
cells. Because IbTx is a selective pharmacological blocker of the large
conductance KCa channel type (20), we suppose that CO
increased large conductance KCa current. Furthermore, the average cell
Rm decreased, as would be excepted if CO
activated outward current. If the hyperpolarization of the membrane
resulted from the enhancement of IbTx-sensitive current, then IbTx
should be a potent depolarizing agent in PACO cells. Indeed, we found
that IbTx depolarized membranes of PACO cells but not those of PAC
cells (estimated to the Em where the current
density was 0 pA/pF); this was corroborated by records of resting
Em on pressurized resistance PA cells. PA smooth
muscle cells have a high resting membrane input resistance, which we found to be 4.7 G; this is close to the value obtained by Park et
al. (29). This corresponds to very low channel activity
near the resting Em (and with 100 nM
intracellular Ca2+) and has the consequence that opening of
very few channels can cause a substantial hyperpolarization
(25). The mean Rm was decreased
from 4.7 to 2.8 G
under chronic CO. This decrease in resistance
corresponded to an increase of conductance of ~530 pS (1/1.89 G
).
KCa current is increased in PACO cells. Acute exogenous CO has been shown to activate KCa and Kv channels, respectively, in rat tail artery smooth muscle cells (40) and in human jejunal circular smooth muscle cells (14). An effect of CO on the delayed rectifier K+ channel, already observed in visceral smooth muscle cells, and on the KN current was excluded, because the increase of outward current we observed was not sensitive to 4-AP, a general blocker of Kv channels. After chronic CO exposure we saw an increase of the global K+ current, and this was associated with an increase of IbTx-sensitive current, probably large conductance KCa current. Thus these observations suggest that this increase of net outward current by exposure to CO is largely mediated by KCa channels. This is supported by experiments showing that an inhibitor of HO (leading probably to a decrease of endogenous CO) reduced KCa currents (43).
Our results demonstrate that Kv and KCa currents coexist in both populations of cells (PAC and PACO) but that their relative contributions in global current changed. Before CO treatment, the large conductance KCa current component accounts for ~9% and tended to increase to ~44% after chronic CO treatment. However, the Kv current component decreased from ~55 to ~38% after CO exposure. These results suggest that CO treatment could induce a differential expression of K+ channels in resistance PA cells. In this regard a recent study has already demonstrated a differential expression of Kv and KCa channels in vascular smooth muscle cells after 1-day culture (35). Because in our experiments we compared electrical properties of the cells using conventional whole cell patch-clamp techniques under the same experimental conditions and, in particular, using the same intracellular free [Ca2+], we cannot explain this increase of KCa current by an increase of intracellular Ca2+. Furthermore, this increase of outward current persisted after several minutes of equilibration of intrapipette solution in the cells. We cannot exclude an effect of CO on KCa channels via activation of guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (2, 39). Indeed, expression of this kinase or another part of the cGMP pathway could be altered. A modification of the Ca2+ dependence of KCa channels, as well as a direct chemical modification of KCa channels by CO, is not excluded, as this was observed in tail artery smooth muscle cells (39). An increase of spark activity could also explain this increase of KCa current, but we should have observed spontaneous transient outward current (STOCs) as we had already observed in these cells (37). Furthermore, this should be tested using perforated-patch experiments on less-modified Ca2+ homeostasis by intrapipette solution. More experiments are needed to explore how CO increases KCa current and how exposure for 3 wk to CO can induce an increase of KCa channel expression leading to an increase in the number of functional channels.Functional impact of KCa channels after chronic CO exposure. CO is also an endogenously generated gas that regulates vascular tone (39). The predominant biological source of CO is from degradation of heme by HO (36). At least two isoforms of HO, HO-1 and HO-2, an inducible and a constitutive isoform, respectively, have been identified and are present in vascular smooth muscle cells (12). Most experiments suggest that endogenously generated CO affects vascular tone in physiological and pathological conditions, but these experiments were performed with an activator/blocker of HO to activate or inhibit the endogenous CO production (39). Moreover, there is no direct evidence that these effects were due to CO, because the effect of chronic exogenous CO on vascular tone is lacking. Furthermore, the physiological and chronic importance of endogenously generated CO on K+ channel functions was not directly studied. Indeed, only studies using a blocker of HO to inhibit the endogenous CO production and then the changes in K+ channel function were performed (18, 21, 43). Interestingly, Zhang et al. (43) demonstrated that an IbTx-sensitive current is decreased after inhibition of HO, suggesting an activating effect of endogenous CO on vascular KCa currents.
PA smooth muscle cells have a high density of KCa channels, and these channels (through STOCs) regulate resting Em of PA smooth muscle cells (3, 37). It has been suggested that, in PA smooth muscle cells, the major role of KCa channels is a negative-feedback mechanism that acts to counteract membrane depolarization (42) and thus membrane contraction. Indeed, the high Rm of PA smooth muscle cells, coupled with the large unitary conductance of large conductance KCa channels, provides this KCa channel with a highly favorable environment in which to buffer membrane depolarization (5). Because they are activated by membrane depolarization and an increase of intracellular Ca2+, they play a minor role in regulating baseline tone of PA. Indeed, although charybdotoxin has little effect under this conditions, this blocker enhances the increase of PA pressure to hypoxia (26). We found significant hyperpolarization of pressurized resistance PA smooth muscle cells after CO, and we demonstrated that resting Em of PACO smooth muscle cells, and not of PAC smooth muscle cells, was sensitive to IbTx. This suggests that KCa were activated after chronic CO exposure and could explain the hyperpolarization of PACO arteries. Indeed, we showed that KCa current was increased in PACO smooth muscle cells. This membrane hyperpolarization not only inactivates voltage-dependent Ca2+ channels but also inhibits agonist-induced increase of inositol triphosphate and reduces Ca2+ sensitivity, leading to vasorelaxation (39). In some cardiovascular pathologies such as systemic arterial hypertension, the expression and activity of KCa are increased, leading to nullified increased tendency of arteries to constrict (22). In contrast to chronic CO, chronic hypoxia-induced pulmonary hypertension is associated with decreased KCa channel activity (30), leading to more depolarized and thus more excitable smooth muscle cells. Furthermore, HO-1 is transiently increased by chronic hypoxia (7) whenever sustained activation prevents the development of hypoxic pulmonary hypertension (8). Furthermore, this increase of KCa currents induced by chronic CO (exogenously or endogenously) may provide a novel target for therapy during pulmonary hypertension as nitric oxide does (1). ![]() |
ACKNOWLEDGEMENTS |
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The authors thank Dr. Christine Barbé, Dr. Annie Rochetaing, and Dr. Paul Kréher for supplying chronic CO rats. We also thank Nadine Gaudin for excellent secretarial support in preparing this manuscript and Jean-Pierre Moisan for technical assistance.
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FOOTNOTES |
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This work was supported by a grant from Agence de l'Environnement et de la Maîtrise d'Energie (98 93 029). We thank le Conseil Regional du Centre, la Fondation de France, and le Ministère de L'Enseignement Supérieur et de la Recherche.
Address for reprint requests and other correspondence: C. Vandier, Laboratoire de Physiopathologie de la Paroi Artérielle, Faculté de Médecine (LABPART), 2 bis Boulevard Tonnellé, 37032 Tours, France (E-mail: vandier{at}univ-tours.fr).
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.
First published February 15, 2002;10.1152/ajplung.00004.2002
Received 7 January 2002; accepted in final form 14 February 2002.
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