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Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
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ABSTRACT |
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 Top
 Abstract
 Introduction
Materials and methods
Results
Discussion
References
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Isolated rat middle cerebral arteries were
perfused and superfused with physiological salt solution equilibrated
with a control (~140 mmHg) or reduced (~35-40 mmHg)
PO2. In other experiments, cerebral
arteries were isolated and prostacyclin release was determined by
radioimmunoassay for 6-ketoprostaglandin F1
.
Equilibration of the vessels with reduced
PO2 (35 mmHg) solution caused a
significant increase in prostacyclin release relative to control PO2 (140 mmHg) conditions. Exposure
of middle cerebral arteries to reduced
PO2 caused vascular smooth muscle (VSM) hyperpolarization and vessel relaxation, which could be blocked
by 1 µM glibenclamide, an inhibitor of the ATP-sensitive K+ channel, but not by 1 mM
tetraethylammonium (TEA), an inhibitor of the
Ca2+-activated
K+ channel. Glibenclamide also
inhibited VSM hyperpolarization and vasodilation in response to the
stable prostacyclin analog iloprost, but TEA did not affect
iloprost-induced dilation of the vessel. Endothelial removal eliminated
the electrical and mechanical responses of the arteries to reduced
PO2, but vessel responses to iloprost
were similar to those of intact vessels. The results of this study are
consistent with the hypothesis that hypoxic dilation of rat middle
cerebral arteries is due to VSM hyperpolarization mediated by
prostacyclin-induced activation of glibenclamide-sensitive K+ channels.
vascular smooth muscle; hypoxia; oxygen; adenosine 5'-triphosphate-sensitive potassium channels; endothelium
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INTRODUCTION |
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Top
Abstract
Introduction
Materials and methods
Results
Discussion
References
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OXYGEN AVAILABILITY is a major factor contributing to the local regulation of blood flow in the cerebral circulation (2). Although there is substantial evidence that changes in the levels of parenchymal cell metabolites play an important role in mediating cerebral vascular responses to changes in PO2 (2, 19), several studies have indicated that isolated cerebral arteries (11, 21, 26, 28) and more recently isolated cerebral arterial muscle cells (12, 23) are directly sensitive to reduced PO2.
Although the precise mechanisms that mediate oxygen "sensing" in the arterial wall are not well defined in cerebral resistance arteries maintained at normal intraluminal pressures and distending forces, a recent study (11) has indicated that the dilation of these vessels in response to reduced PO2 is mediated by endothelium-derived cyclooxygenase products that activate glibenclamide-sensitive K+ channels in the arterial smooth muscle cells. Other studies (20) have demonstrated that exposure of skeletal muscle resistance arteries to reduced PO2 leads to an increased release of prostacyclin from the vessels.
If prostacyclin release mediates hypoxic relaxation of cerebral resistance arteries by activating glibenclamide-sensitive K+ channels, exposure of the vessels to reduced PO2 should cause an increased release of prostacyclin and a hyperpolarization of the vascular smooth muscle cells that can be blocked by glibenclamide, an inhibitor of the ATP-sensitive K+ channels (KATP). Furthermore, exogenous addition of a prostacyclin analog should cause a glibenclamide-sensitive hyperpolarization of the arterial smooth muscle.
In the present study we tested this hypothesis directly by determining the electrical and mechanical responses of isolated middle cerebral arteries of the rat to reduced PO2 and to the stable prostacyclin analog iloprost before and after removal of the vascular endothelium and by measuring prostacyclin release in isolated cerebral arteries during exposure to reduced PO2. We also tested the ability of glibenclamide to inhibit the electrical and mechanical responses of the vessel to reduced PO2 and iloprost. The results of this study are consistent with the hypothesis that hypoxic relaxation of cerebral resistance arteries is mediated by vascular smooth muscle hyperpolarization that results from the activation of glibenclamide-sensitive K+ channels in response to increased prostacyclin release during exposure to reduced PO2.
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MATERIALS AND METHODS |
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Top
Abstract
Introduction
Materials and methods
Results
Discussion
References
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General procedures. Male Sprague-Dawley rats (Sasco-King, Madison, WI) were anesthetized with pentobarbital sodium (60 mg/kg ip). The brain was removed and the proximal portion of the middle cerebral artery (100-250 µm inner diam) was carefully isolated and placed in warmed physiological salt solution (PSS). The PSS was bubbled with 21% O2-7% CO2-balance N2 and had the following constituents (in mM): 119 NaCl, 4.7 KCl, 1.17 MgSO4, 1.6 CaCl2, 1.18 NaH2PO4, 24 NaHCO3, 0.026 EDTA, and 5.5 glucose.
After isolation the arteries were placed in a heated (37°C) superfusion and perfusion chamber and cannulated with tapered glass micropipettes (100-200 µm diam). The inflow pipette was connected to a reservoir system that allowed the intraluminal pressure and gas concentrations of the luminal perfusate to be controlled. The vessels were secured with 10-0 nylon suture (22 µm diam; Look, Norwell, MA), and all side branches were tied off with a single strand teased from 2-0 silk suture (Ethicon, Somerville, NJ). The artery was then stretched to approximately its in situ length, and intraluminal pressure was set at 80 mmHg. After mounting was completed, the artery was allowed to equilibrate for 30 min with continuous superfusion and perfusion of the lumen with PSS equilibrated with 21% O2. Vessel diameters were measured by television microscopy, as previously described (10, 11). Vascular smooth muscle transmembrane potentials were measured with a high-impedance amplifier and glass microelectrodes (40-80 M
impedance) filled with 3 M KCl. Criteria for a successful impalement
included an abrupt drop to a steady level of transmembrane potential
for a minimum of 5 s and an abrupt return to baseline on exit of the electrode from the cell. Five measurements were made under each condition, and the results were averaged to obtain the final value of
transmembrane potential for that vessel under each experimental condition.
Reactivity of the arteries was assessed by verifying the ability of the
vessel to contract in response to a brief exposure to 100 nM serotonin.
Endothelial function was verified by demonstrating that the
serotonin-contracted vessels dilated in response to 1 µM
acetylcholine, and the presence of intrinsic tone in the artery was
verified at the end of the experiment by demonstrating that the vessel
dilated in response to Ca2+-free
solution. In some experiments the endothelium was removed by perfusing
the vessel lumen with an air bolus, as described previously (10, 11).
After air perfusion the lumen was again perfused with PSS, and the
effectiveness of endothelial removal was verified by constricting the
vessel with serotonin and demonstrating a lack of dilation in response
to 1 µM acetylcholine. Any vessel that was unresponsive to serotonin,
the initial application of acetylcholine, or
Ca2+-free solution was not used in
the study.
Effects of reduced PO2 on resting diameter and vascular smooth muscle transmembrane potential. After the control equilibration at 21% O2, vessel diameters and vascular smooth muscle transmembrane potential were measured before and during a simultaneous reduction of the oxygen concentration of the PSS in the tissue bath (superfusate) and inflow reservoir (luminal perfusate). Superfusate PO2 was reduced by bubbling the PSS with a 0% O2-7% CO2-93% N2 gas mixture using air stones in the supply reservoir and vessel chamber and by covering the vessel chamber with glass microscope slides except during diameter or membrane potential measurements. Perfusate PO2 was reduced by bubbling the PSS in the perfusion reservoir with the same gas mixture and by using gas-impermeable delivery lines. These procedures result in a reduction of both perfusate and superfusate PO2 from the control value of ~140 mmHg during 21% O2 perfusion and superfusion to ~35-40 mmHg during equilibration of the perfusion and superfusion reservoirs with the 0% O2 gas mixture (10).
Effect of glibenclamide and TEA on electrical and mechanical response of rat middle cerebral arteries to reduced PO2 and iloprost. To evaluate the role of KATP in mediating the relaxation of rat middle cerebral arteries in response to decreased oxygen availability, we determined the effect of glibenclamide on the electrical and mechanical responses of the vessels to reduced PO2 and iloprost (a stable analog of prostacyclin, the putative mediator of hypoxic relaxation in these vessels). Vascular smooth muscle transmembrane potentials and arterial diameters were measured before and during 0% O2 perfusion and superfusion and before and during superfusion with 10 pg/ml iloprost. In these experiments, the electrical and mechanical responses to reduced PO2 and iloprost were determined before and 30 min after addition of 1 µM glibenclamide (an inhibitor of KATP) to the superfusate.
In previous experiments (11) we demonstrated that dilation of rat middle cerebral artery in response to reduced PO2 was not affected by inhibition of the high-conductance, Ca2+-activated K+ channels (KCa) with tetraethylammonium (TEA). In the present study we confirmed and extended these findings by measuring vessel diameter and vascular smooth muscle transmembrane potential before and during exposure to reduced PO2 in the presence of 1 mM TEA. To exclude a contribution of KCa in mediating prostacyclin-induced dilation of these vessels, we also tested the response of the vessels to 10 pg/ml iloprost before and after inhibiting KCa with 1 mM TEA. In the latter experiments, the change in arterial diameter in response to 10 pg/ml iloprost was determined before and 30 min after the addition of 1 mM TEA to the superfusate.Response of endothelium-denuded vessels to reduced PO2 and iloprost. The electrical and mechanical responses of the vessels to hypoxia and iloprost were also tested after removal of the vascular endothelium to determine whether either of these vasodilator stimuli had direct effects on the arterial smooth muscle cells. In these experiments, vessel diameters and vascular smooth muscle transmembrane potentials were measured in endothelium-denuded vessels before and during reduction of perfusate and superfusate PO2 and before and during superfusion with iloprost (10 pg/ml).
Assessment of prostacyclin release.
In another series of experiments, middle cerebral arteries and other
small arteries of similar size (200-350 µm) were isolated from
the cerebral circulation. Vessels were pooled in each animal, weighed,
and cut into small segments. Approximately 10 mg of tissue were placed
in a glass centrifuge tube containing 2 ml of PSS. The vessel segments
were incubated for 1 h during normoxic conditions while the reaction
mixture was bubbled with the 21%
O2 gas mixture, which produced a
PO2 of 140-150 mmHg in the tube.
The 21% O2 control period was
followed by a 1-h exposure to a reduced PO2 of ~35 mmHg. This
PO2 was chosen to match the
PO2 levels that exist in the
perfusion and superfusion solutions during equilibration with 0%
O2 gas mixture in the cannulated vessel experiment (10) and was achieved by direct equilibration of the
PSS in the centrifuge tube with a 5%
O2 gas mixture. At the end of each
equilibration period, the incubation medium was drawn off and acidified
to pH 3.5 with 1 M formic acid, and acidic lipids were extracted twice
with two volumes (4 ml) of ethyl acetate. The ethyl acetate was back
extracted with 1 ml of water to remove residual acidity, dried down
under nitrogen, and stored at 
80°C until radioimmunoassay.
(6-keto-PGF1), a stable metabolite
of prostacyclin, in the incubation medium. Measurements were made by
radioimmunoassay using a
125I-labelled
6-keto-PGF1 kit and antibody purchased from PerSeptive Diagnostics (Cambridge, MA).
Statistical analysis. In all experiments data were summarized as means ± SE. Differences between multiple means were assessed using ANOVA with a subsequent Newman-Keuls test. A paired Student's t-test was used to assess the dilation of the vessels in response to a single reduction of perfusate and superfusate oxygen concentration. P < 0.05 was considered to be statistically significant.
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RESULTS |
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Top
Abstract
Introduction
Materials and methods
Results
Discussion
References
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Effect of reduced PO2 on
vascular smooth muscle transmembrane potential and diameter of isolated
rat middle cerebral arteries.
Figure 1 shows a typical recording of
vascular smooth muscle transmembrane potential during perfusion and
superfusion of an isolated rat middle cerebral artery with PSS
equilibrated with the 21% O2 gas
mixture. Transmembrane potential during that recording was 41
mV, which was typical for resting values in the smooth muscle cells of
the middle cerebral artery during normoxic control conditions. Figure
2 summarizes the effect of perfusion and
superfusion with the reduced PO2
solution on vascular smooth muscle transmembrane potential and the
diameter of rat middle cerebral arteries. Exposure to the reduced
PO2 solution caused a significant
hyperpolarization of the vascular smooth muscle cells and an increase
in vessel diameter that was similar to that reported in our previous
studies (11).
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Effect of glibenclamide and TEA on electrical and mechanical
responses of rat middle cerebral artery to reduced
PO2.
Figure 3 shows the effects of 1 µM
glibenclamide on resting diameter and vascular smooth muscle
transmembrane potential under control conditions (21%
O2 perfusion and superfusion), and
Fig. 4 summarizes the effect of 1 µM
glibenclamide on the electrical and mechanical responses of isolated
rat middle cerebral arteries to reduced
PO2. In these experiments
glibenclamide caused vascular smooth muscle depolarization and
vasoconstriction during the control condition (Fig. 3) and eliminated
the vascular smooth muscle hyperpolarization and the dilation of the
vessels in response to reduced PO2
(Fig. 4).
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Effect of iloprost on vascular smooth muscle transmembrane potential
and diameter of rat middle cerebral arteries.
The effect of the stable prostacyclin analog iloprost on vascular
smooth muscle transmembrane potential and diameter in isolated rat
middle cerebral arteries with an intact endothelium is summarized in
Fig. 6. Iloprost caused a significant
hyperpolarization of the vascular smooth muscle and a dilation of the
vessel that were both inhibited by 1 µM glibenclamide. In contrast to
the inhibitory effect of 1 µM glibenclamide on iloprost-induced
dilation, the dilation of the vessels in response to iloprost was not
affected by 1 mM TEA (Fig. 7).
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Response to hypoxia and iloprost in endothelium-denuded vessels.
The electrical and mechanical responses of rat middle cerebral arteries
to hypoxia and iloprost after endothelial removal are summarized in
Fig. 8. Removal of the endothelium
eliminated both the dilation and the vascular smooth muscle
hyperpolarization in response to perfusion and superfusion with the
reduced PO2 solution. However,
endothelium-denuded arteries still dilated and exhibited vascular
smooth muscle hyperpolarization in response to iloprost.
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Release of prostacyclin by rat cerebral arteries during exposure to
reduced PO2.
Figure 9 summarizes the release of
6-keto-PGF1, the stable metabolite of prostacyclin, by
small cerebral arteries during equilibration with control (21%
O2) and reduced (5%
O2)
PO2 solution. In these experiments,
6-keto-PGF1 release increased significantly during
incubation with the reduced PO2 solution.
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DISCUSSION |
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Top
Abstract
Introduction
Materials and methods
Results
Discussion
References
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We have demonstrated previously that isolated middle cerebral arteries of rats are intrinsically sensitive to reduced PO2, showing hypoxic dilation independent of the influence of parenchymal cell metabolites (11). The findings of the present study confirm those results and provide new evidence supporting a role for prostacyclin-induced activation of glibenclamide-sensitive K+ channels in the vascular smooth muscle cells as a mechanism for hypoxic dilation of this vessel.
The intrinsic sensitivity of different blood vessels to changes in oxygen availability has been reported to reside either at the level of the vascular smooth muscle cells themselves (12, 23) or to depend on the presence of an intact endothelium (4, 5, 24, 30, 31). Previous studies in our laboratory (11) have indicated that the endothelium is the major oxygen sensor regulating intrinsic tone in unstimulated rat middle cerebral arteries maintained at normal levels of transmural pressure. In those studies, dilation of the vessels in response to reduced PO2 was eliminated either by removal of the endothelium or by perfusion of the vessel lumen with normoxic solution, even when the outside of the vessel was bathed with reduced PO2 solution. In the present study, exposure of the vessels to the reduced PO2 solution was associated with vasodilation and vascular smooth muscle hyperpolarization, and these responses were eliminated by endothelial removal (Fig. 8). These new findings provide evidence that hypoxic dilation of the rat middle cerebral artery is mediated via changes in vascular smooth muscle transmembrane potential and that the hyperpolarization and relaxation of these vessels in response to reduced PO2 is endothelium dependent.
Two major endothelium-derived relaxing vasodilator substances that have
been proposed to mediate relaxation of vascular smooth muscle in
response to reduced PO2 are nitric
oxide (NO; 29-31) and vasodilator products of the cyclooxygenase
pathway of arachidonic acid metabolism (4, 18, 24). In our earlier experiments (11), 1 µM indomethacin prevented the dilation of the
arteries in response to reduced PO2,
whereas the NO synthase inhibitor
N
-nitro-L-arginine (10 µM) did
not. The latter observations suggested that the chemical mediator which
inhibits intrinsic tone in rat middle cerebral arteries during exposure
to reduced PO2 is a vasodilator
product of the cyclooxygenase pathway rather than NO.
One likely candidate for an endothelium-derived mediator of hypoxic
relaxation in these vessels is prostacyclin (20). At the present time
there is considerable controversy regarding the role of prostacyclin
and other cyclooxygenase products in mediating hypoxic dilation
[see Pearce (27) for review]. These studies, based largely
on the use of cyclooxygenase inhibitors, suggest that there may be
considerable regional and species-dependent differences in the
contribution of prostacyclin to the response of blood vessels to
reduced PO2. In the present study, we
demonstrated that exposure of rat cerebral arteries to reduced PO2 is associated with an increase in
the release of the stable prostacyclin metabolite
6-keto-PGF1 by the vessels. These direct measurements of
an increased release of prostacyclin metabolites during exposure to
reduced PO2 are consistent with a
role for prostacyclin in mediating hypoxic relaxation of these vessels.
In this respect the dilation of rat cerebral arteries in response to
reduced PO2 appears to involve
mechanisms similar to those proposed for hypoxic inhibition of
spontaneous tone in rat cremasteric arterioles (24) and
extraparenchymal resistance arteries of skeletal muscle (10) but
different from the NO-dependent relaxation of phenylephrine-contracted
rat aorta in response to reduced PO2
(13).
The role of vascular smooth muscle transmembrane potential in regulating the response of resistance arteries to changes in oxygen availability has not been widely studied. Several mechanisms other than a primary change in transmembrane potential have been proposed to affect the active tone of vascular smooth muscle during changes in oxygen availability, including changes in Ca2+ influx into the smooth muscle cells (9) or a direct regulation of contractile filament Ca2+ sensitivity by changes in PO2 (32). Other reports have suggested that electrophysiological mechanisms contribute to the relaxation of blood vessels in response to reduced PO2 (14, 21). However, Pearce (27) noted that the membrane potential changes in one of these studies (14) were complete at PO2 values that were higher than those expected to be encountered during hypoxic dilation in vivo. The present study demonstrates that reduction of perfusate and superfusate PO2 to 35-40 mmHg leads to a significant hyperpolarization of the vascular smooth muscle of rat middle cerebral arteries, supporting the hypothesis that electrophysiological mechanisms play an important role in regulating active tone in cerebral resistance arteries during changes in oxygen availability that could be encountered physiologically.
The most likely mechanism for vascular smooth muscle hyperpolarization in response to reduced PO2 is activation of K+ channels in the vascular smooth muscle cell membrane (3, 11, 33). Several studies in the literature (8, 22, 25, 34) and our own studies in rat middle cerebral artery (11) suggest that glibenclamide- sensitive K+ channels mediate the dilation of various blood vessels in response to reduced PO2, and hypoxia has been reported to activate KATP in isolated smooth muscle cells from the pig coronary artery (7). In contrast, studies of isolated smooth muscle cells of the cat middle cerebral artery suggest that low PO2 activates high-conductance KCa in the arterial smooth muscle cell membrane (12). In that study hypoxic dilation of the cat middle cerebral artery and the increase in the open state probability of KCa in patch-clamped arterial smooth muscle cell membranes during exposure to reduced PO2 were both blocked by 1 mM TEA.
In addition to a direct effect of reduced PO2 on the vascular smooth muscle cells, K+ channels could be activated by vasodilator substances released from the endothelium or the parenchymal cells. For example, recent studies (6) indicate that cGMP mediated vasodilators relax mesenteric microvessels by opening KCa. The latter mechanism could be important in mediating any component of hypoxic dilation that is due to cGMP dependent mechanisms such as NO (13, 29).
In the present experiments both the dilation and the vascular smooth muscle hyperpolarization occurring in rat middle cerebral arteries during exposure to reduced PO2 were eliminated by 1 µM glibenclamide, which at this concentration inhibits KATP in arterial smooth muscle cells by 80-90% without modifying KCa current (1, 35). Blockade of KATP with glibenclamide also led to vascular smooth muscle depolarization and constriction of the middle cerebral artery under normoxic resting conditions. The latter observation is consistent with the studies of Jackson (15), who demonstrated that arterioles in the hamster cheek pouch and cremaster muscle constrict in response to glibenclamide, suggesting that KATP contribute to the regulation of arteriolar tone in these tissues under resting conditions. In contrast, blockade of KCa with 1 mM TEA led to vasoconstriction and vascular smooth muscle depolarization under resting conditions but did not prevent the vascular smooth muscle hyperpolarization and vasodilation occurring in these vessels in response to reduced PO2. The latter observations suggest that KCa contribute to the regulation of resting tone in the vessels but do not mediate dilation and vascular smooth muscle hyperpolarization in response to hypoxia. These data support and extend the results of our previous studies (11), which demonstrated that the dilation of rat middle cerebral artery in response to reduced PO2 was blocked by 1 µM glibenclamide but was unaffected by 1 mM TEA. Taken together, these observations provide further evidence in support of the hypothesis that the relaxation of rat middle cerebral artery in response to reduced PO2 is due to vascular smooth muscle hyperpolarization mediated by the opening of KATP channels.
As noted above the activation of KATP in the arterial smooth muscle cell membrane during exposure to hypoxia could be due either to a direct action of reduced PO2 on the vascular smooth muscle cell or to the action of vasodilator substances released from the endothelium or parenchymal cells in response to reduced oxygen availability. The latter hypothesis is consistent with reports that both adenosine (25) and prostacyclin (15, 16) activate glibenclamide-sensitive K+ channels and that glibenclamide inhibits hypoxic dilation in rabbit pial arterioles (34) and isolated guinea pig hearts (8).
Previous studies in our laboratory have demonstrated that indomethacin and glibenclamide both inhibit the relaxation of rat middle cerebral artery in response to reduced PO2 (11). In the present experiments we demonstrated that reduced PO2 also increases prostacyclin release by rat cerebral arteries. Therefore, we hypothesized that exogenous addition of iloprost, a stable analog of prostacyclin, would result in a hyperpolarization and relaxation of the vascular smooth muscle. The present studies support this hypothesis by demonstrating that iloprost causes a significant dilation and hyperpolarization of the vascular smooth muscle of the rat middle cerebral artery. The electrical and mechanical responses of endothelium-denuded vessels to iloprost were similar to those of intact vessels, indicating that the relaxing effect of the prostacyclin released during hypoxia is mediated by a direct effect on the vascular smooth muscle cells.
The vascular smooth muscle hyperpolarization and relaxation of the arteries in response to iloprost were both eliminated by glibenclamide in the present study. Glibenclamide not only blocks dilation of the rat middle cerebral artery in response to reduced PO2 (Fig. 4 and Ref. 11) but also inhibits hypoxic coronary vasodilation (8) and prostacyclin-induced dilation in the coronary circulation (16) and in the microcirculation of the hamster cheek pouch and cremaster muscle (15). In contrast to the inhibitory effect of glibenclamide on iloprost- and hypoxia-induced dilation of the rat middle cerebral artery, the dilation of these vessels in response to iloprost (Fig. 7) and hypoxia (Fig. 5) in the present study were unaffected by TEA, a blocker of the KCa. In conjunction with the observations that hypoxia increases prostacyclin release by cerebral arteries (Fig. 9), that glibenclamide inhibits hypoxic dilation of these vessels (Fig. 4), and that iloprost causes hyperpolarization and dilation of endothelium-denuded middle cerebral arteries (Fig. 8), these observations are consistent with the hypothesis that increased prostacyclin release during hypoxia leads to dilation of the rat middle cerebral artery by activating KATP channels in the vascular smooth muscle membrane. In view of the observation that endothelial cells of some blood vessels have KATP channels (17), one question that remains unanswered is whether the inhibitory effect of glibenclamide on hypoxic dilation of rat middle cerebral artery is due solely to the blockade of KATP channel activation in the vascular smooth muscle cells or whether blockade of KATP channels on the endothelial cells can also inhibit prostacyclin release during hypoxia.
Regardless of any possible effect of glibenclamide on prostacyclin release by the vessels, the results of the present experiments support the hypothesis that the dilation of rat middle cerebral artery in response to reduced PO2 is mediated by vascular smooth muscle hyperpolarization due to the opening of KATP in response to endothelium-derived prostacyclin. The activation of KATP channels by endothelium-dependent vasodilators such as prostacyclin may represent an important mechanism by which opening of these channels contributes to vasodilation during moderate reductions of PO2 (10, 11), rather than having their contribution restricted to conditions of severe PO2 reduction, where ATP depletion would cause the channel to be activated.
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ACKNOWLEDGEMENTS |
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We thank Luellen Lougee and Tianjian Huang for excellent technical assistance; Camille Torres and Meredith Skelton for assistance in the measurements of prostacyclin release; and Terri Harrington, Susan Raschka, and Kathy Valent for the outstanding secretarial assistance.
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FOOTNOTES |
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We also thank Berlex Laboratories (Wayne, NJ) for the generous gift of iloprost for these experiments.
This work was supported by National Heart, Lung, and Blood Institute Grants HL-37374, HL-29587, and HL-52211.
Present address of Kim T. Fredricks: Dept. of Biology, Viterbo College, LaCrosse, WI 54601.
Requests for reprints: J. H. Lombard, Dept. of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226.
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. §1734 solely to indicate this fact.
Received 30 January 1998; accepted in final form 13 October 1998.
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Top
Abstract
Introduction
Materials and methods
Results
Discussion
References
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Significant
difference in response to reduced PO2
relative to that determined in absence of glibenclamide in same
vessels. Glibenclamide eliminated hyperpolarization and dilation of
vessels in response to perfusion and superfusion with reduced
PO2 solution.
