(Hypertension. 1995;26:1035-1040.)
© 1995 American Heart Association, Inc.
Articles |
Prostacyclin Synthesis Elicited by Endothelin-1 in Rat Aorta Is Mediated by an ETA Receptor via Influx of Calcium and Is Independent of Protein Kinase C
From the Department of Pharmacology, College of Medicine, The University of Tennessee, Memphis.
Correspondence to K.U. Malik, PhD, DSc, Department of Pharmacology, College of Medicine, The University of Tennessee, 874 Union Ave, Memphis, TN 38163. E-mail kmalik@utmem1.utmem.edu.
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Abstract |
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Abstract The purpose of this study was to characterize the receptor(s) and second messenger systems involved in prostacyclin (prostaglandin [PG] I2) synthesis elicited by endothelin (ET)-1 in the rat aorta. PGI2 synthesis, measured as immunoreactive 6-keto-PGF1
, was assessed in aortic
rings exposed to endothelin receptor agonists in the presence and
absence of selective ETA and ETB receptor
antagonists. ET-1, which has equal affinity for both
endothelin receptor subtypes, and ET-3, a preferential ETB
receptor agonist, enhanced
6-keto-PGF1 synthesis in a time-
and concentration-dependent manner. ET-1 was more potent than ET-3
in increasing 6-keto-PGF1
synthesis. Moreover, the selective ETB receptor agonists
IRL-1620 and sarafotoxin S6c did not significantly increase
6-keto-PGF1 synthesis.
Furthermore, ET-1–induced
6-keto-PGF1 synthesis was
attenuated by an ETA receptor antagonist,
BQ-123, in a dose-dependent manner but not by an ETB
receptor antagonist, BQ-788. Depletion of extracellular
Ca2+ or addition of Ca2+ channel
blockers (nifedipine, verapamil, SK&F 96365)
attenuated ET-1–mediated
6-keto-PGF1 synthesis, while a
Ca2+ channel agonist, S(-)-Bay K
8644, potentiated this effect of ET-1. Selective protein kinase C
inhibitors (bisindolylmaleimide I, calphostin C) did not
alter ET-1–induced 6-keto-PGF1
synthesis. These data suggest that PGI2 synthesis elicited
by ET-1 in the rat aorta is mediated primarily through influx of
extracellular Ca2+ via activation of an
ETA receptor and is independent of protein kinase C.
Key Words: receptors • endothelin • prostaglandins • calcium • aorta
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Endothelin, which was isolated 7 years ago from porcine endothelial cells, is the most potent vasoconstrictor agent yet discovered, eliciting a long-lasting pressor response when injected intravenously.1 It has been implicated in a variety of cardiovascular diseases, such as atherosclerosis, hypertension, and renal failure.2 Three structurally and pharmacologically distinct isoforms of endothelin (ET-1, ET-2, and ET-3), each consisting of 21 amino acids, have been identified. Endothelins have been reported to produce their biological actions through two distinct subtypes of receptor: ETA and ETB. These receptors contain seven putative transmembrane domains and are coupled to G proteins. ET-1 binds to ETA receptors with a 2- to 10-fold higher affinity than ET-2 and a greater than 100-fold higher affinity than ET-3. The ETB receptor has a similar affinity for all three isopeptides. Recent studies indicate the presence of subtypes of the ETB receptor and of a third type of endothelin receptor (ETC) that displays a high affinity for ET-3.3
The vasoconstriction elicited by ET-1 can occur through both ETA and ETB receptors, depending on the tissue and species studied.4 5 Vasoconstriction is preceded by a transient vasodilation both in vitro6 and in vivo.1 The dilator component of the response to ET-1 can be mimicked by a selective ETB receptor agonist, IRL-1620,7 and blocked in vivo by the selective ETB receptor antagonist BQ-788.8 The mechanism is still unresolved; however, both prostacyclin (PGI2) and endothelium-derived relaxing factor have been implicated.9 Although both mediators oppose vascular smooth muscle contractions elicited by endothelin,10 their role in the direct vasodilator response to endothelin is still unclear.
Endothelins stimulate prostanoid synthesis in vascular smooth
muscle,11 12 kidney,13 14
spleen,10 heart,15 and some types of vascular
endothelial cell16 (although perhaps not
all17 ). The site of PGI2 synthesis and the
type of receptor involved in the action of endothelin to promote
prostanoid synthesis in various tissues have not been clearly
established. The purpose of this study was to determine the site of
PGI2 synthesis in rat aortic rings and the subtype of
endothelin receptor involved in stimulating PGI2 synthesis.
The effect of ET-1, ET-3, and selective ETB receptor
agonists
Suc-[Glu9,Ala11,15]-endothelin-1(8-21)
(IRL-1620)18 and sarafotoxin S6c,19 as well
as the effect of ET-1 in the presence of selective ETA and
ETB receptor antagonists
cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp)
(BQ-123)20 and
N-cis-2,6-dimethyl-piperidinocarbonyl-L-
-methylleucyl-D-1-methoxycarbonyl-tryptophanyl-D-norleucine
(BQ-788),8 respectively, on PGI2 synthesis in
rat aortic rings was examined. Since endothelin has been reported to
increase Ca2+ influx1 21 and PKC
activity22 in some tissues, we further examined the effect
of extracellular Ca2+ depletion,
Ca2+ channel blockers, and PKC
inhibitors on ET-1–induced PGI2
production in the rat aorta.
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Methods |
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Preparation of Aortic Rings
The following protocol was reviewed and approved by the Animal Care and Use Committee of our institution and conforms to the Guide for the Care and Use of Laboratory Animals (National Institutes of Health). The preparation of aortic rings was adapted from a previous method.23 Male Sprague-Dawley rats (weight, 300 to 350 g; Charles River, Wilmington, Mass) were anesthetized with pentobarbital (50 mg/kg IP), and the thoracic aortas were removed and placed in a 37°C BSS containing the following (mmol/L): NaCl 116, KCl 5.4, MgCl2 · 6H2O 1.2, NaH2PO4 · H2O 1.2, CaCl2 · 2H2O 1.8, glucose 5.5, and HEPES 25 (pH 7.4). Fat and connective tissue were carefully removed as well as the small blood vessels branching out from the aorta. The aortas were then cut into 0.2-cm-wide rings. For each experiment, aortas from 2 to 3 rats were pooled.
Protocol 1
The first series of experiments was conducted to determine the
time course and the effect of different concentrations of endothelin
receptor agonists on 6-keto-PGF1
production in rat aortic rings. The aortic rings were placed in
24-well plates (Falcon) and equilibrated with gentle shaking in 1 mL of
BSS in a water bath at 37°C. The BSS was replaced each time at the
end of four 30-minute incubation periods. These incubation periods were
necessary to stabilize the initial high basal output of
6-keto-PGF1. Separate groups of
aortic rings were then incubated with 1 mL BSS containing 100 nmol/L of
either ET-1, ET-3, IRL-1620, sarafotoxin S6c, or respective vehicle for
5, 10, 20, and 30 minutes. The aortic rings were removed at the
previously specified time points and blotted on a paper towel to
determine ring wet weight (milligrams). The incubation medium was
assayed the same day for
6-keto-PGF1 content as described
below. Basal PGI2 synthesis was defined as picograms
6-keto-PGF1 per milligram
tissue, and the effect of the agonists was expressed as a percentage of
the basal value. In an additional series of experiments, separate
groups of aortic rings were incubated in 1 mL BSS containing different
concentrations (0.5 to 500 nmol/L) of either ET-1, ET-3, IRL-1620,
sarafotoxin S6c, or vehicle for a period of 20 minutes. The rings were
removed and weighed, and the incubation medium was assayed for
6-keto-PGF1 content.
Protocol 2
This series of experiments was performed to investigate the
effect of removal of the endothelium on
6-keto-PGF1 synthesis elicited by ET-1. We removed the
endothelium by cutting the aorta open to expose the
intima and then gently brushing the intima with a moistened cotton
swab. This method was successful in removing the
endothelium as confirmed by
histological staining with hematoxylin and eosin. The
experimental protocol included two groups of aortic rings:
endothelium-intact and
endothelium-denuded. After a stabilization period
of 120 minutes (four changes of BSS), the rings were incubated with 1
mL BSS containing either ET-1 (10 nmol/L) or vehicle for 20 minutes.
The BSS was then removed, and the rings were weighed.
Protocol 3
This series of experiments was performed to determine the effect
of selective ETA (BQ-123) and ETB (BQ-788)
receptor antagonists on ET-1–induced
6-keto-PGF1 synthesis. The
aortic rings were equilibrated with BSS as described above, except that
during the last 30-minute incubation period an appropriate
concentration of antagonist or vehicle was added. The BSS
was removed and then replaced with fresh BSS containing ET-1 (10
nmol/L) in the presence or absence of the antagonist. After
a 20-minute incubation period, the rings were removed and weighed, and
the remaining buffer was saved for measurement of
6-keto-PGF1.
Protocol 4
This series of experiments was conducted to determine the effect
of depletion of extracellular Ca2+,
Ca2+ channel blockers, and a Ca2+
channel agonist on ET-1–induced 6-keto-PGF1
synthesis. The aortic rings were equilibrated with normal BSS as
described above, and then half were incubated with ET-1 (10 nmol/L) in
normal BSS and the other half with 10 nmol/L ET-1 in
Ca2+-free BSS. After a 20-minute incubation period,
the rings were removed and weighed and the remaining buffer was saved.
To determine the effect of Ca2+ channel blockers or
a Ca2+ channel agonist on ET-1–stimulated
6-keto-PGF1 synthesis, aortic rings were
equilibrated with normal BSS as described above and then preincubated
with or without either nifedipine (10 µmol/L),
verapamil (10 µmol/L) (L-type Ca2+
channel blockers),24 SK&F 96365 (1 µmol/L)
(receptor-operated Ca2+ channel
blocker),25 S(-)-Bay K 8644 (100 nmol/L)
(L-type Ca2+ channel agonist),26 or
their respective vehicle for 10 minutes. The BSS was then removed and
replaced with BSS containing ET-1 (10 nmol/L) or vehicle with or
without the respective Ca2+ channel modulators for
20 minutes. The rings were then removed and weighed and the remaining
buffer was saved.
Protocol 5
The last series of experiments was performed to investigate the
contribution of PKC to PGI2 synthesis elicited by ET-1. The
protocol was identical to that described above for the
Ca2+ channel blockers, except that the selective PKC
inhibitors calphostin C (100 nmol/L),27 Bis I
HCl (20 nmol/L),28 or their vehicle were added to the
medium, and the aortic rings were preincubated for 30 minutes. In an
additional series of experiments, PKC activity was measured under
identical conditions through modification of a method described
previously.29 In brief, aortas (one half aorta per
experimental treatment) were frozen with liquid nitrogen and pulverized
into powder form. All subsequent procedures were performed at 4°C.
The powder was homogenized in a tissue-tearer
homogenizer (Fisher) in 1 mL of buffer (pH 7.5)
containing (mmol/L) Tris-HCl 20, sucrose 300, EDTA 0.5, EGTA 0.5,
ß-mercaptoethanol 10, and 0.025 mg/mL each of leupeptin and
aprotinin. The homogenates were then centrifuged at
6000g for 20 minutes, the supernatant was removed, and the
protein concentration was determined, with bovine serum albumin
as a standard (BioRad). The PKC activity of each supernatant was
determined with the use of a PKC enzyme assay kit (Amersham Life
Science) under the conditions specified in the instruction manual, with
1 µg of protein per reaction tube and an incubation time of 15
minutes. PKC activity was expressed as picomoles per minute per
milligram protein.
Radioimmunoassay of 6-Keto-PGF1
The content of 6-keto-PGF1 (a stable product of
PGI2 hydrolysis) in the incubation buffer was determined by
radioimmunoassay as previously described.30 Briefly,
50-µL samples were mixed with 3000 to 4000 cpm tracer plus an
appropriate concentration of antibody in polystyrene tubes. Tracer and
antibody were prepared in buffer containing (g/L) NaN3
1.0, NaCl 9.0, KH2PO4 6.8,
K2HPO4 26.1, and gelatin 2.0. Tubes were then
vortexed and incubated overnight at 4°C. One milliliter of
dextran-coated charcoal was added to each tube to separate bound
from free tracer, and radioactivity was determined by liquid
scintillation spectroscopy. The antibody for
6-keto-PGF1 was kindly provided by Dr C.
Leffler (University of Tennessee, Department of Physiology).
Cross-reactivity of the 6-keto-PGF1
antibody was less than 0.1% with thromboxane B2;
13,14-dihydro-15-keto-PGF2; and PGI2 and less
than 0.5% with PGE2 and
PGF1. Furthermore, none of the drugs
used in this study were found to interfere with the
radioimmunoassay.
Drugs
The drugs used in this study are as follows: ET-1, ET-3, and
BQ-123 (gift) from Peninsula Laboratories, Inc; sarafotoxin S6c from
Sigma Chemical Co; BQ-788 from American Peptide Company;
nifedipine from Pfizer Inc; verapamil from
Knoll Pharmaceutical Co; calphostin C and SK&F 96365 from Biomol;
S(-)-Bay K 8644 from Research Biochemicals
International; and Bis I HCl from Calbiochem. Stock solutions of
calphostin C, nifedipine, verapamil, and
S(-)-Bay K 8644 were prepared in dimethyl sulfoxide;
SK&F and Bis I were prepared in water. All peptides were stored in
water diluted with glacial acetic acid at -80°C until use,
except for BQ-788, which was stored in methanol. All of these compounds
were diluted in BSS before their use. For all experiments, the effect
of the appropriate vehicle was also determined.
Statistical Analysis
The results are expressed as the mean±SEM percent change from
basal values. Data were analyzed by one-way ANOVA; the
unpaired Student's t test was applied to determine the
difference between two groups. A value of P
.05 was
considered significant. Basal PGI2 output
represents the amount of PGI2 in samples collected
after removal of BSS and is expressed as picograms of immunoreactive
6-keto-PGF1 per milligram of tissue.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Effect of ET-1 and ET-3 and Endothelin Receptor Agonists on 6-Keto-PGF1
Synthesis in Rat Aortic
RingsIncubation of rat aortic rings with ET-1 and ET-3 resulted in a time-dependent increase in 6-keto-PGF1
production (Fig 1, top panel).
6-Keto-PGF1 synthesis elicited by ET-1 was
detected within 5 minutes and peaked at 20 minutes. ET-3–induced
6-keto-PGF1 synthesis was detectable within
10 minutes and reached a maximum at 30 minutes. ET-1 was clearly more
efficacious in stimulating 6-keto-PGF1
synthesis than ET-3. Neither sarafotoxin S6c nor IRL-1620 caused a
significant increase in 6-keto-PGF1
synthesis over the observed 30-minute time period. Incubation of aortic
rings with increasing concentrations of ET-1 and ET-3 enhanced
PGI2 synthesis in a dose-dependent manner (Fig 1, bottom panel). ET-1 and ET-3 maximally stimulated
6-keto-PGF1 synthesis at concentrations of
50 nmol/L and at least 500 nmol/L, respectively, while higher
concentrations of either peptide did not increase PGI2
synthesis any further and in fact caused a decrease in
6-keto-PGF1 output. As expected,
neither sarafotoxin S6c nor IRL-1620 caused a significant increase in
6-keto-PGF1 synthesis at the concentrations
used (data not shown).
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Effect of ET-1 on 6-Keto-PGF1 Synthesis
in Endothelium-Denuded Rat Aortic Rings
The basal synthesis of
6-keto-PGF1 did not
significantly differ between endothelium-denuded
and endothelium-intact aortic rings (322±97 versus
319±67 pg/mg tissue, respectively). Furthermore, ET-1 (10
nmol/L)–elicited 6-keto-PGF1 synthesis was
still evident in the endothelium-denuded aortic
rings and was not significantly different from that of
endothelium-intact rings (5227±383 versus
4883±396 pg/mg tissue, respectively; P>.1, n=12).
Effect of Endothelin Receptor Antagonists on
ET-1–Induced 6-Keto-PGF1 Synthesis in Rat
Aortic Rings
BQ-123, a selective ETA receptor
antagonist, produced a dose-dependent decrease in
ET-1–induced 6-keto-PGF1 synthesis, whereas
a selective ETB receptor antagonist, BQ-788,
was without effect (Fig 2). Additionally,
ET-3–induced 6-keto-PGF1 synthesis was
attenuated by BQ-123 (data not shown). Neither of the
antagonists altered the basal output of
6-keto-PGF1 or interfered with the
conversion of exogenously added arachidonic acid to
6-keto-PGF1 (data not shown).
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significantly different from that of ET-1
in the absence of a receptor antagonist
(P
Effect of Extracellular Ca2+ Depletion,
Nifedipine, Verapamil, SK&F 96365, and Bay K
8644 in ET-1–Stimulated 6-Keto-PGF1
Synthesis in Rat Aortic Rings
The removal of extracellular Ca2+ significantly
diminished ET-1–induced 6-keto-PGF1
synthesis in aortic rings (Fig 3). Furthermore,
the removal of Ca2+ caused a significant increase in
basal PGI2 synthesis above that of rings incubated in the
presence of calcium. The L-type Ca2+ channel
blockers nifedipine and verapamil and the
receptor-operated Ca2+ channel blocker SK&F
96365 significantly inhibited ET-1–stimulated
6-keto-PGF1 synthesis in aortic rings (Fig 4, top panel). The L-type
Ca2+ channel agonist Bay K 8644, which prevents the
closure of the channel, potentiated ET-1–elicited PGI2
synthesis, and this effect was blocked by nifedipine and to
a lesser extent by SK&F 96365 (Fig 4, bottom panel).
Neither of the agents altered the basal output of
6-keto-PGF1 or interfered with the
conversion of exogenously added arachidonic acid to
6-keto-PGF1 (data not shown).
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significantly different from ET-1 and nifedipine;
§significantly different from ET-1 and SK&F 96365; ¶significantly
different from Bay K 8644 and ET-1 (P
Effect of PKC Inhibitors on ET-1–Stimulated
6-Keto-PGF1 Synthesis and PKC Activity in
Rat Aortic Rings
Neither of the PKC inhibitors used in this study, Bis
I or calphostin C, significantly affected basal or ET-1–induced
6-keto-PGF1 synthesis in rat aortic rings.
ET-1 (10 nmol/L)–induced
6-keto-PGF1 production
in rat aortic rings was 786±44% above basal (433±75 pg/mg
6-keto-PGF1), which was not
significantly different from that of ET-1 in the presence of 20 nmol/L
Bis I (815±64% above basal) or 100 nmol/L calphostin C (890±139%
above basal) (P>.1, n=8 to 10). Under identical conditions,
ET-1 increased PKC activity in aortic rings, and this increase was
attenuated by the aforementioned PKC inhibitors
(Table).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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This study indicates that ET-1 promotes prostacyclin synthesis via activation of an ETA subtype of receptor located in the smooth muscle layer of the rat aorta by increasing influx of extracellular Ca2+ through a PKC-independent mechanism. ET-1 enhanced PGI2 production, measured as 6-keto-PGF1
, in rat aortic rings
in a concentration-dependent manner. Our finding that ET-1–induced
6-keto-PGF1 synthesis is
inhibited by an ETA receptor antagonist
(BQ-123) but not by an ETB receptor antagonist
(BQ-788) suggests that ET-1 promotes
6-keto-PGF1 production via
activation of an ETA receptor in rat aorta. At the higher
dose of ET-1 the effect of BQ-123 was less pronounced; however, the
concentration of BQ-123 used may not have been sufficient to overcome
the effect of ET-1, which has a greater affinity for the
ETA receptor than BQ-123.3 Supporting our
conclusion that ET-1 promotes 6-keto-PGF1
production via activation of an ETA receptor is our
observation that ETB receptor agonists IRL-1620 and
sarafotoxin S6c, in concentrations known to stimulate vasoactivity in
the rat aorta and other tissues,7 19 did not significantly
increase production of
6-keto-PGF1. ET-3, which
has 100-fold less affinity for ETA than ETB
receptors, was also much less potent than ET-1 in stimulating
6-keto-PGF1 production. The rank
order of potencies for 6-keto-PGF1 synthesis
in the rat aorta (ET-1ET-3>IRL-1620=sarafotoxin S6c) for the
different endothelin receptor agonists exhibited the profile of a
ETA receptor.31 ET-1–induced PGI2
synthesis in the kidney has also been reported to be mediated by an
ETA receptor.14
Molecular and pharmacological studies have shown that both
ETA and ETB receptors are present in
vascular smooth muscle, whereas only ETB receptors are
present in vascular endothelium.32 33 34
Our finding that removal of endothelium did not alter
ET-1–induced 6-keto-PGF1
production in rat aortic rings suggests that the
ETA receptor coupled to PGI2 production
is located in the smooth muscle layer. However, further studies in the
cultured smooth muscle and fibroblast cells from the rat aorta are
required to establish conclusively the site of the ETA
receptor coupled to PGI2 production, since the
adventitia of the aorta contains fibroblasts, which express
ETA and ETB receptors in some
tissues.35 These observations would suggest that the
vasodilation elicited by ET-1 in the rat7 8 and other
species,36 which has been reported to be mediated by
ETB receptors, is unlikely to be dependent on
PGI2 production.
ET-1 has been reported to increase influx of extracellular
Ca2+1 21 and also mobilize
intracellular Ca2+ from endoplasmic
reticulum.37 Activation of ETA receptors by
ET-1 may increase cytosolic Ca2+ and
activate one or more lipases to release
arachidonic acid for PGI2 synthesis. Our
demonstration that removal of extracellular Ca2+
completely abolished ET-1–induced
6-keto-PGF1 production
suggests that ET-1 promotes prostanoid production by increasing
the influx of extracellular Ca2+. Interestingly,
removal of Ca2+ from the BSS caused an increase in
6-keto-PGF1 production
compared with that of aortic rings incubated in normal BSS. This effect
could be due to activation of a Ca2+-independent
phospholipase A238 and/or a decreased
reacylation of endogenous arachidonic acid.
Further experiments using a selective inhibitor of the
Ca2+-independent phospholipase A2 and/or
radiolabeled arachidonic acid will be necessary to
explain this result of Ca2+ depletion.
The L-type Ca2+ channel blockers
nifedipine and verapamil diminished the effect
of ET-1 to stimulate 6-keto-PGF1
production. These observations suggest that ET-1 promotes
influx of Ca2+ required for
6-keto-PGF1 synthesis via L-type
Ca2+ channels. Supporting this view was our finding
that an L-type Ca2+ channel agonist, Bay K 8644,
produced a small but significant increase in
6-keto-PGF1 production
and markedly potentiated ET-1–induced
6-keto-PGF1 synthesis, which was
attenuated by nifedipine. Since the depletion of
extracellular Ca2+ but not nifedipine
and verapamil completely abolished ET-1–induced
6-keto-PGF1 production,
it appears that ET-1 promotes influx of Ca2+ for
prostanoid synthesis also via receptor-operated
Ca2+ channels. This conclusion is supported by our
demonstration that a reported receptor-operated
Ca2+ channel antagonist, SK&F 96365,
also reduced ET-1–induced
6-keto-PGF1 synthesis in rat
aortic rings. Moreover, the combination of nifedipine or
verapamil and SK&F 96365 produced a greater reduction in
ET-1–induced 6-keto-PGF1
production than each of these agents alone. Since SK&F 96365
abolished the potentiating effect of Bay K 8644 on ET-1–induced
6-keto-PGF1 synthesis, we cannot
exclude the possibility that SK&F 96365 reduces ET-1–induced
6-keto-PGF1 synthesis by a
nonspecific action on voltage-gated Ca2+
channels. Recently, it has been reported that SK&F 96365 in high
concentrations inhibits cyclooxygenase
activity.39 However, this seems unlikely in the
present study because SK&F 96365, in concentrations that inhibited
ET-1–stimulated 6-keto-PGF1
synthesis, did not alter the conversion of exogenously added
arachidonic acid to
6-keto-PGF1 in rat aortic rings
(data not shown).
The increase in Ca2+ influx could stimulate
phospholipase A2 activity to release
arachidonic acid for prostanoid synthesis via
activation of one or more protein kinases. Endothelin has been reported
to increase PKC activity in various tissues,22 and PKC can
phosphorylate and increase the activity of a
Ca2+-dependent phospholipase
A2.40 In our study treatment of aortic rings
with ET-1 increased PKC activity, which was prevented by PKC
inhibitors. However, the PKC inhibitors did not
alter the production of
6-keto-PGF1 elicited by ET-1. We
are now investigating the role of other protein kinases, including
mitogen-activated protein kinase and
Ca2+-calmodulin–dependent protein
kinases, in the release of arachidonic acid for
PGI2 production in the rat aorta.
The present study demonstrates that ET-1 stimulates
6-keto-PGF1 production
via activation of an ETA receptor, probably located in the
smooth muscle layer of rat aortic rings. Activation of ETA
receptors by ET-1 promotes influx of extracellular
Ca2+ via voltage- as well as receptor-operated
Ca2+ channels, which in turn stimulates
PGI2 production by a mechanism independent of
PKC.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This study was supported in part by National Institutes of Health (Heart, Lung, and Blood Institute) grant HL-19134-20. H.M.W. was supported in part by National Research Service Award, Pre-Doctoral Research Training grant HL-07641-06. This work was done in partial fulfillment of requirements for the degree of Doctor of Philosophy by H.M.W. We wish to thank Anne Estes for technical assistance and Linda Mann for histological staining of tissue samples.
Received June 17, 1995; first decision August 18, 1995; accepted September 5, 1995.
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References |
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