PGE2 triggers recovery of transmucosal resistance
via EP receptor cross talk in porcine ischemia-injured
ileum
Anthony T.
Blikslager,
Susan M.
Pell, and
Karen M.
Young
Department of Clinical Sciences, College of Veterinary Medicine,
North Carolina State University, Raleigh, North Carolina 27606
 |
ABSTRACT |
16,16-Dimethyl-PGE2 (PGE2) may interact
with one of four prostaglandin type E (EP) receptors, which signal via
cAMP (via EP2 or EP4 receptors) or
intracellular Ca2+ (via EP1 receptors).
Furthermore, EP3 receptors have several splice variants,
which may signal via cAMP or intracellular Ca2+. We sought
to determine the PGE2 receptor interactions that mediate recovery of transmucosal resistance (R) in
ischemia-injured porcine ileum. Porcine ileum was subjected to
45 min of ischemia, after which the mucosa was mounted in
Ussing chambers. Tissues were pretreated with indomethacin (5 µM).
Treatment with the EP1, EP2, EP3,
and EP4 agonist PGE2 (1 µM) elevated
R twofold and significantly increased tissue cAMP content,
whereas the EP2 and EP4 agonist deoxy-PGE1 (1 µM) or the EP1 and
EP3 agonist sulprostone (1 µM) had no effect. However, a
combination of deoxy-PGE1 and sulprostone stimulated
synergistic elevations in R and tissue cAMP content. Furthermore, treatment of tissues with deoxy-PGE1 and the
Ca2+ ionophore A-23187 stimulated synergistic increases in
R and cAMP, indicating that PGE2 triggers
recovery of R via EP receptor cross talk mechanisms
involving cAMP and intracellular Ca2+.
mucosa; barrier function; adenosine 3',5'-cyclic monophosphate; G
protein; short-circuit current
 |
INTRODUCTION |
16,16-DIMETHYL-PGE2
(PGE2) stimulates recovery of barrier function in porcine
ischemia-injured ileal mucosa, but the PGE2 receptor interactions involved in this model are unknown
(3-5). PGE2 may interact with at least
four cell surface prostaglandin type E receptors (EP1,
EP2, EP3, and EP4), which trigger a
variety of intracellular responses depending on which G protein they
are coupled to (12, 17). For example, PGE2
stimulates production of cAMP via EP2 and EP4
receptors linked to Gs protein (6, 21) but
inhibits production of cAMP via EP3 receptors coupled to
Gi protein (8, 19, 24). Furthermore,
PGE2 may increase intracellular Ca2+ via
EP1 (29) and EP3 (16)
receptors through Gq protein-phospholipase C interactions.
From previous studies (5), we know that porcine mucosal
tissue cAMP is elevated in response to PGE2 and that the phosphodiesterase inhibitor theophylline heightens the effect of
PGE2 on recovery of transmucosal resistance (R).
Although this data implicates a role for EP2 or
EP4 receptors coupled to Gs protein, we do not
know whether EP receptors that increase intracellular Ca2+
are also involved. Studies indicate a critical role for the
EP3 receptor in duodenal bicarbonate secretion in mice
(26, 27) and for PGE2-stimulated
cytoprotection of gastric parietal cells (22). Work from
other laboratories indicates that EP1, EP3, and
EP4 mRNA have all been detected in the mucosa or submucosa of the mouse (15) and rat (9), whereas
EP2 receptor mRNA was not detected in the gastrointestinal
tract of rodents. However, EP2 receptors have been detected
in normal and inflamed human colonic mucosal epithelium
(25).
In the present study, we sought to determine the nature of
PGE2-EP receptor interactions involved in
PGE2-stimulated recovery of R through a series
of experiments using receptor-specific agonists and antagonists. Our
data indicate that the response of ischemia-injured porcine
ileal mucosa to PGE2 involves an intriguing cross talk mechanism between EP receptors linked to the generation of cAMP and
intracellular Ca2+, respectively.
 |
MATERIALS AND METHODS |
Experimental animal surgeries.
All studies were approved by the North Carolina State University
Institutional Animal Care and Use Committee. Six- to eight-wk-old Yorkshire crossbred pigs of either sex were housed singularly and
maintained on a commercial pelleted feed. Pigs were held off feed for
24 h before experimental surgery. General anesthesia was induced
with xylazine (1.5 mg/kg im), ketamine (11 mg/kg im), and pentobarbital
sodium (15 mg/kg iv) and maintained with intermittent infusion of
pentobarbital sodium (6-8
mg · kg
1 · h
1). Pigs were
placed on a heating pad and ventilated with 100% O2 via a
tracheotomy by using a time-cycled ventilator. The jugular vein and
carotid artery were cannulated, and blood gas analysis was performed to
confirm normal pH and partial pressures of CO2 and
O2. Lactated Ringer solution was administered intravenously at a maintenance rate of 15 ml · kg
1 · h
1. Blood
pressure was continuously monitored via a transducer connected to the
carotid artery. The ileum was approached via a ventral midline
incision. Ileal segments were delineated by ligating the intestinal lumen at 10-cm intervals and were subjected
to ischemia by clamping the local mesenteric blood supply
for 45 min.
Ussing chamber studies.
After the ischemic period, the mucosa was stripped from the
seromuscular layer in oxygenated (95% O2-5%
CO2) Ringer solution and mounted in
3.14-cm2-aperture Ussing chambers, as described previously
(1). Tissues were bathed on the serosal and mucosal sides
with 10 ml Ringer solution. The serosal bathing solution contained 10 mM glucose and was osmotically balanced on the mucosal side with 10 mM
mannitol. Bathing solutions were oxygenated (95% O2-5%
CO2) and circulated in water-jacketed reservoirs. The
spontaneous potential difference (PD) was measured using Ringer-agar
bridges connected to calomel electrodes, and PD was short-circuited
through Ag-AgCl electrodes using a voltage clamp that corrected for
fluid resistance. R (in
· cm2) was
calculated from the spontaneous PD and short-circuit current (Isc). If the spontaneous PD was between
1 and
1 mV, tissues were current clamped at ±100 µA for 5 s and the
PD was recorded. Isc and PD were recorded every
15 min for 4 h.
Experimental treatments.
Tissues were bathed in Ringer containing 5 µM indomethacin to prevent
PG production while mucosa was stripped from the seromuscular tissues,
and indomethacin was added to the serosal and mucosal bathing solutions
in the same concentration before tissues were mounted on Ussing
chambers. Other treatments that were added before baseline electrical
measurements were SC-19220 (Cayman Chemical), AH-6809 (Biomol),
pertussis toxin, or TTX (Sigma Chemical, St. Louis, MO). Baseline
electrical readings were taken for 30 min, after which further
treatments were added to the tissues depending on the study. Treatments
added after the 30-min equilibration included PGE2,
A-23187, thapsigargin (Sigma Chemical), sulprostone, 11-deoxy-PGE1, misoprostol, or
11-deoxy-16,16-dimethyl-PGE2 (Cayman Chemical).
cAMP RIA.
Tissues were removed from Ussing chambers once
Isc peaked in response to receptor agonists and
were immediately frozen in liquid N2. Tissues were stored
at
70°C before extraction and RIA. One part tissue (100 mg) was
homogenized with nine parts 5% TCA. The homogenate was centrifuged at
2,500 g at 4°C for 15 min and extracted three times with 5 vol of water-saturated ether. Excess ether was discarded after each
extraction, and the samples were evaporated to dryness. RIA for cAMP
was performed using a commercial kit according to the manufacturer's
instructions (Biomedical Technologies, Stoughton, MA).
Data analysis.
Data are reported as means ± SE. All data were analyzed using an
ANOVA for repeated measures except when the peak response was analyzed
using a standard one-way ANOVA or paired t-test (Sigmastat, Jandel Scientific, San Rafael, CA). Tukey's test was used to determine differences between treatments after ANOVA, and P < 0.05 was considered significant.
 |
RESULTS |
Ischemia-injured tissues bathed in indomethacin (5 µM)
and treated with the EP1, EP2, EP3,
and EP4 agonist PGE2 (1 µM) after a 30-min
equilibration period showed marked elevations in R compared with tissues treated with indomethacin alone (Fig.
1A). However, neither the
EP2 and EP4 agonist deoxy-PGE1 (1 µM) nor the EP1 and EP3 agonist sulprostone
(1 µM) had any effect on R, whereas a combination of
deoxy-PGE1 and sulprostone stimulated synergistic elevations in R similar in magnitude to that of
PGE2 (Fig. 1A). Because we have previously shown
that recovery of R is preceded by increases in
Isc (3, 5), we also evaluated
Isc data for the presence of similar trends
(Fig. 1B). Accordingly, there was no effect of
either deoxy-PGE1 or sulprostone on
Isc, but a combination of the two agents
triggered elevations in Isc similar in magnitude to that of PGE2.

View larger version (25K):
[in this window]
[in a new window]
|
Fig. 1.
Electrical responses of ischemia-injured tissues
treated with various prostanoid type E (EP) receptor agonists.
A: serosal addition of the EP1, EP2,
EP3, and EP4 receptor agonist
16,16-dimethyl-PGE2 (PGE2; 1 µM) to
ischemia-injured tissues after an initial 30-min equilibration
period resulted in ~2-fold elevations in transmucosal resistance
(R), whereas treatment of tissues with the EP2
and EP4 receptor agonist deoxy-PGE1 (1 µM) or
the EP1 and EP3 receptor agonist sulprostone (1 µM) had no apparent effect. However, addition of
deoxy-PGE1 and sulprostone stimulated synergistic
elevations in R. B: elevations in R
after treatment with PGE2 or deoxy-PGE1 + sulprostone were preceded by elevations in short-circuit current
(Isc). Values are means ± SE;
n = 6. The significance of the synergism between
deoxy-PGE1 and sulprostone was determined using 2-way ANOVA
on repeated measures (P < 0.05).
|
|
Because we have previously demonstrated that elevations in R
in response to PGE2 were correlated with elevations in
tissue cAMP (5), we next measured cAMP levels in response to various prostanoids. Tissues were taken for measurement of cAMP
immediately after peak Isc response. In
ischemia-injured tissues treated with PGE2, cAMP
was elevated approximately twofold compared with tissues treated with
indomethacin alone (Fig. 2). Although
neither sulprostone nor deoxy-PGE1 triggered elevations in
cAMP above that of indomethacin-treated tissues, a combination of
sulprostone and deoxy-PGE1 elevated cAMP approximately
twofold, similar to the effect of PGE2. These data
suggested cross talk between EP receptors wherein stimulation of
EP2 or EP4 Gs-linked receptors with
deoxy-PGE1 was insufficient to trigger a rise in cAMP, but
concurrent stimulation of EP1 or EP3 receptors
resulted in elevations in cAMP.

View larger version (35K):
[in this window]
[in a new window]
|
Fig. 2.
Tissue homogenate cAMP content in tissues treated with
various EP receptor agonists. Tissues were removed from Ussing chambers
after peak Isc. Tissues treated with
PGE2 (1 µM) or deoxy-PGE1 + sulprostone
(1 µM) had significant elevations in cAMP compared with tissues
treated with indomethacin alone or tissues additionally treated with
sulprostone or deoxy-PGE1. cAMP elevations correlated with
electrical data in that only treatments that triggered significant
elevations in cAMP had elevated Isc and
R. Values are means ± SE; n = 6. * P < 0.05 vs. tissues treated with indomethacin,
indomethacin + deoxy-PGE1, or indomethacin + sulprostone (1-way ANOVA).
|
|
EP1 receptors are coupled to Gq protein that
results in increases in intracellular Ca2+ via
activation of phospholipase C (11), whereas
EP3-G protein interactions depend on COOH terminal splice
variation of EP3 transcripts. There are at least four
EP3 splice variants: EP3A coupled to
Go/Gi protein, EP3B and
EP3C coupled to Gs protein, and
EP3D coupled to Gq protein (16).
To exclude a role for EP1 receptors in the response of
tissues to PGE2 or deoxy-PGE1 plus sulprostone,
tissues were pretreated with the EP1 receptor antagonists
SC-19220 or AH-6809. However, these antagonists had no effect on either
PGE2 (Table 1) or sulprostone
plus deoxy-PGE1-triggered elevations (data not shown) in
R or Isc at doses of 1-100 µM.
This agreed with other studies (18) indicating that
sulprostone has a preferential action on EP3 receptors.
View this table:
[in this window]
[in a new window]
|
Table 1.
Effect of EP1 receptor antagonists on peak Isc
and R in ischemia-injured porcine ileum treated with
indomethacin and 16,16-dimethyl PGE2
|
|
We next focused on which of the EP3 receptor splice
variants was involved in the response of tissues to PGE2.
Because Go and Gi proteins have an inhibitory
action on neuronal Ca2+ channels and adenylyl cyclase,
respectively (10), it seemed unlikely that
EP3A would be responsible for the stimulatory action of
prostanoids on R and Isc in
ischemia-injured ileum. To further exclude a role for
EP3A receptors, ischemia-injured tissues were pretreated for up to 60 min with 125 mg/ml pertussis toxin (to which
Go and Gi proteins are sensitive) and
subsequently treated with PGE2 or sulprostone plus
deoxy-PGE1. However, pertussis toxin had no effect on
measurements of R and Isc (Table 1).
Because Go protein is largely expressed in neuronal tissue
(10), we also pretreated tissues with TTX (0.1 µM), but
this neuronal inhibitor had no effect on subsequent treatment of
ischemia-injured tissues with PGE2 (Table 1) or
sulprostone plus deoxy-PGE1 (data not shown).
Of the remaining splice variants of EP3, EP3D
linked to Gq protein, with associated elevations in
intracellular Ca2+, was considered the most likely
candidate for a cross talk response with EP2- or
EP4-linked Gs protein. Therefore, tissues were
treated with deoxy-PGE1 and the calcium ionophore A-23187
(0.1 µM) to stimulate increases in Ca2+ independent of
receptor interactions. Treatment of tissues with A-23187 stimulated
increases in R compared with tissues treated with
indomethacin alone (Fig. 3A).
However, treatment of tissues with deoxy-PGE1 and A-23187
triggered synergistic elevations in R, and evaluation of
Isc revealed similar trends (Fig.
3B). In addition, tissue cAMP measurements indicated that
A-23187 in combination with deoxy-PGE1 stimulated
significant elevations in cAMP, whereas neither A-23187 nor
deoxy-PGE1 had any effect when given alone (Fig.
4). Although these results were
suggestive of a role for intracellular Ca2+ in the cross
talk response between EP receptors, A-23187 can also elevate
phospholipid second messengers via stimulation of phospholipase C
(13). Therefore, we next used thapsigargin, which has been
shown to elevate intracellular Ca2+ from intracellular and
extracellular Ca2+ sources without stimulating other second
messenger signaling mechanisms (13). Tissues were treated
with combinations of thapsigargin (0.1 µM) and deoxy-PGE1
(1 µM) that, similar to experiments with A-23187 and
deoxy-PGE1, induced synergistic elevations in R
and Isc (Fig. 5).
Thus elevations in intracellular Ca2+ appeared critical to
the cross talk response with Gs-linked EP receptors.

View larger version (23K):
[in this window]
[in a new window]
|
Fig. 3.
Electrical responses of tissues treated with the calcium
ionophore A-23187 and deoxy-PGE1. A: tissues
treated with A-23187 (0.1 µM) had transient elevations in
R, whereas tissues treated with deoxy-PGE1 (1 µM) did not differ in R from tissues treated with
indomethacin alone. However, tissues treated with both A-23187 and
deoxy-PGE1 had synergistic elevations in R,
suggesting a requirement for elevated Ca2+ in the response
of tissues to prostanoid agonists. B: similar trends were
noted in the Isc responses of tissues to A-23187
and deoxy-PGE1. Values are means ± SE;
n = 6. The significance of the synergistic response
between A-23187 and deoxy-PGE1 was determined using 2-way
ANOVA on repeated measures (P < 0.05).
|
|

View larger version (35K):
[in this window]
[in a new window]
|
Fig. 4.
Tissue homogenate cAMP content in tissues treated with
A-232187 and/or deoxy-PGE1. Tissues were removed from
Ussing chambers after peak Isc. Tissues treated
with A-23187 (1 µM) and deoxy-PGE1 (1 µM) had
significant elevations in cAMP compared with tissues treated with
indomethacin + A-23187 or indomethacin + deoxy-PGE1. These data suggest that the EP2 and
EP4 receptor agonist deoxy-PGE1 only triggers
elevations in cAMP in the presence of elevated intracellular
Ca2+. Values are means ± SE; n = 6. * P < 0.05 vs. tissues treated with
indomethacin + A-23187 or indomethacin + deoxy-PGE1 (paired t-test).
|
|

View larger version (24K):
[in this window]
[in a new window]
|
Fig. 5.
Electrical responses of tissues treated with
thapsigargin, which elevates intracellular Ca2+, and
deoxy-PGE1. A: synergistic elevations in
R in tissues treated with thapsigargin (0.1 µM) and
deoxy-PGE1 (1 µM) were noted that were qualitatively
similar to those of tissues treated with A-23187 and
deoxy-PGE1, indicating that an increase in intracellular
Ca2+ is required for the full tissue response to E-type
prostanoids. B: synergistic elevations in
Isc were also noted in tissues treated with
thapsigargin and deoxy-PGE1. Values are means ± SE;
n = 6. The significance of the synergistic response
between thapsigargin and deoxy-PGE1 was determined using
2-way ANOVA on repeated measures (P < 0.05).
|
|
In additional experiments, we sought to determine whether the activity
of PGE2 could be accounted for by solely by activation of
EP2 and EP3 receptors. The tissue R
and Isc response to PGE2 (1 µm)
was compared with that of the EP2 and EP3
receptor agonists misoprostol (1 µM) or
11-deoxy-16,16-dimethyl-PGE2 (1 µM) (27). The tissue R and Isc responses to
these agonists were similar in magnitude to those of PGE2
(Fig. 6). Together, our data indicate that EP2 and EP3 receptors were the most likely
receptors involved in the response of ischemia-injured porcine
ileum to PGE2 (Table 2).

View larger version (23K):
[in this window]
[in a new window]
|
Fig. 6.
Electrical responses of tissues treated with the
EP2 and EP3 agonists misoprostil and
11-deoxy-16,16-dimethyl PGE2. A: elevations in
R similar to those of PGE2 (1 µM) were noted
in tissues treated with misoprostil (1 µM) or 11-deoxy-16,16-dimethyl
PGE2 (1 µM), suggesting that the action of
PGE2 could be reproduced by agonists that activate only
EP2 and EP3 receptors. B: similar
elevations in Isc were also noted in tissues
treated with misoprostil and 11-deoxy-16,16-dimethyl PGE2.
Values are means ± SE; n = 6. The significance of
the elevations in R and Isc noted in
tissues treated with PGE2, misoprostil, or
11-deoxy-16,16-dimethyl PGE2 was determined using 2-way
ANOVA on repeated measures (P < 0.05).
|
|
View this table:
[in this window]
[in a new window]
|
Table 2.
Expected receptor interaction and peak electrical responses in
ischemia-injured porcine ileum treated with various
prostanoids
|
|
 |
DISCUSSION |
In previous studies (3, 4), we postulated that
PGE2 triggers recovery of R of
ischemia-injured porcine ileum by stimulating closure of
interepithelial spaces via cAMP. For example, PGE2 stimulated increases in tissue cAMP, PGE2-induced recovery
of R was heightened by the phosphodiesterase inhibitor
theophylline, and addition of cAMP to ischemic-injured tissues
simulated the action of PGE2 (4, 5). The
present studies confirm an important role for cAMP in
PGE2-stimulated increases in R but indicate that EP receptor cross talk mechanisms are required to initiate generation of cAMP at prostanoid doses of 1 µm. This premise is based on the
fact that deoxy-PGE1, an agonist that interacts with the
Gs protein-linked EP2 and EP4
receptors, was without effect on R or tissue cAMP levels
unless it was applied to ischemia-injured tissue together with
an agent that induces increases in intracellular Ca2+. Such
agents included the Ca2+ ionophore A-23187 and
thapsigargin. Candidate EP receptors that also trigger increases in
intracellular Ca2+ were EP1 and
EP3D receptors (16, 29), of which the
EP3D receptor appeared to be the most likely candidate,
because EP1 receptor antagonists failed to inhibit the
action of PGE2. In addition, two agonists that do not
purportedly act on EP1 receptors (the EP2/EP3 receptor agonists misoprostol
and 11-deoxy-16,16-dimethyl PGE2; Ref. 20)
simulated the action of PGE2 (27).
Furthermore, the fact that an EP2 and EP3
agonist simulated the action of PGE2 suggested that, of the
Gs protein-linked EP receptors, EP2 was most
likely involved in the response of ischemia-injured tissue to
PGE2.
Although specific EP receptors have been implicated in various
physiological responses of the gut to PGE2 (2,
26), we are not aware of reports implicating cross talk between
EP receptors. However, there are reports of cross talk between
Gq and Gs protein-linked receptors in other
tissues that we believe are relevant to the present study
(23). For example, in cardiac fibroblasts, muscarinic agonists that signal increases in intracellular Ca2+ via
Gq protein potentiated elevations in cAMP stimulated by
2-agonists, which signal via Gs protein
(14). Mechanisms proposed to account for Gq
and Gs protein cross talk included stimulation of
Ca2+/calmodulin sensitive adenylyl cyclase and release of

-subunits, which act on adenylyl cyclase, by activated
Gq protein (14). Although measurements of
tissue cAMP in the present study allowed us to define prostanoid
interactions required to activate adenylyl cyclase, the precise nature
of intracellular Ca2+ signals could not be determined
because of the complexity of native mucosa. However, based on
experiments with A-23187 and thapsigargin, it appears that increased
intracellular Ca2+ (and not activation of Gq
protein per se) is required to activate adenylyl cyclase. Therefore,
there may be other mediators triggered by intracellular
Ca2+ that subsequently activate adenylyl cyclase. For
example, increased intracellular Ca2+ may activate protein
kinase C, which may in turn act on adenylyl cyclase (14).
One other mechanism that should be considered in the development of
cross talk between intracellular Ca2+ and Gs
protein-mediated agonists is the synergistic effect of Ca2+
and cAMP on intestinal epithelial Cl
secretion. Such
synergism has been attributed to Ca2+-induced opening of
basolateral K+ channels, which increases the electromotive
driving force for secretion of Cl
, and cAMP-induced
opening of apical Cl
channels (7, 28). This
may be relevant to the current study, because elevations in
R were consistently preceded by elevations in
Isc, which we (3) have previously
attributed to Cl
secretion. However, the synergism
documented in the present study appears to relate to the necessity for
increases in intracellular Ca2+ to induce elevations in
cAMP, rather than an interaction between Ca2+ and cAMP. The
transient nature of elevations in R in the presence of
deoxy-PGE1 and A-23187 or thapsigargin was somewhat
puzzling considering that PGE2, which we presume also
elevates intracellular Ca2+ via EP3 receptors,
had a more prolonged effect. One possible explanation is that A-23187
and thapsigargin induce only transient elevations in intracellular
Ca2+. Such a transient response to A-23187 has been
documented (7) in other intestinal tissues.
Having defined some of the complexities of PGE2 receptor
signaling in ischemia-injured porcine ileum, the clinical
relevance of these findings may be considered. In general, we have
previously shown (3) that PGE2-induced elevations in
R result in enhanced recovery of intestinal barrier
function, based on mucosal-to-serosal fluxes of macromolecules such as
mannitol and morphological evidence of "tightening" of
interepithelial spaces. Although the current study confirms
that a range of prostanoid agonists are capable of triggering increases
in R, it appears that agents that selectively interact with
EP2 and EP3 receptors are capable of
reproducing the action of PGE2, thereby lessening potential
side effects of universal activation of all EP receptors.
 |
ACKNOWLEDGEMENTS |
This work was supported by National Institute of Diabetes and
Digestive and Kidney Diseases Grant DK-53284 (A. T. Blikslager).
 |
FOOTNOTES |
Present address of S. Pell: Weston Creek Veterinary Hospital, 200 Badimara St., Waramanga ACT 2611, Australia.
Address for reprint requests and other correspondence: A. T. Blikslager, College of Veterinary Medicine, North Carolina State Univ., 4700 Hillsborough St., Raleigh, NC 27606 (E-mail:
Anthony_Blikslager{at}ncsu.edu).
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.
Received 21 December 2000; accepted in final form 21 March 2001.
 |
REFERENCES |
1.
Argenzio, RA,
and
Liacos JA.
Endogenous prostanoids control ion transport across neonatal porcine ileum in vitro.
Am J Vet Res
51:
747-751,
1990[ISI][Medline].
2.
Belley, A,
and
Chadee K.
Prostaglandin E(2) stimulates rat and human colonic mucin exocytosis via the EP(4) receptor.
Gastroenterology
117:
1352-1362,
1999[ISI][Medline].
3.
Blikslager, AT,
Roberts MC,
and
Argenzio RA.
Prostaglandin-induced recovery of barrier function in porcine ileum is triggered by chloride secretion.
Am J Physiol Gastrointest Liver Physiol
276:
G28-G36,
1999[Abstract/Free Full Text].
4.
Blikslager, AT,
Roberts MC,
Rhoads JM,
and
Argenzio RA.
Prostaglandins I2 and E2 have a synergistic role in rescuing epithelial barrier function in porcine ileum.
J Clin Invest
100:
1928-1933,
1997[Abstract/Free Full Text].
5.
Blikslager, AT,
Roberts MC,
Young KM,
Rhoads JM,
and
Argenzio RA.
Genistein augments prostaglandin-induced recovery of barrier function in ischemia-injured porcine ileum.
Am J Physiol Gastrointest Liver Physiol
278:
G207-G216,
2000[Abstract/Free Full Text].
6.
Breyer, RM,
Davis LS,
Nian C,
Redha R,
Stillman B,
Jacobson HR,
and
Breyer MD.
Cloning and expression of the rabbit prostaglandin EP4 receptor.
Am J Physiol Renal Fluid Electrolyte Physiol
270:
F485-F493,
1996[Abstract/Free Full Text].
7.
Cartwright, CA,
McRoberts JA,
Mandel KG,
and
Dharmsathaphorn K.
Synergistic action of cyclic adenosine monophosphate- and calcium-mediated chloride secretion in a colonic epithelial cell line.
J Clin Invest
76:
1837-1842,
1985[ISI][Medline].
8.
Chen, MC,
Amirian DA,
Toomey M,
Sanders MJ,
and
Soll AH.
Prostanoid inhibition of canine parietal cells: mediation by the inhibitory guanosine triphosphate-binding protein of adenylate cyclase.
Gastroenterology
94:
1121-1129,
1988[ISI][Medline].
9.
Ding, M,
Kinoshita Y,
Kishi K,
Nakata H,
Hassan S,
Kawanami C,
Sugimoto Y,
Katsuyama M,
Negishi M,
Narumiya S,
Ichikawa A,
and
Chiba T.
Distribution of prostaglandin E receptors in the rat gastrointestinal tract.
Prostaglandins
53:
199-216,
1997[Medline].
10.
Dolphin, AC.
G proteins.
In: Textbook of Receptor Pharmacology, edited by Foreman JC,
and Johansen T.. New York: CRC, 1996, p. 187-196.
11.
Funk, CD,
Furci L,
Fitzgerald GA,
Grygorczyk R,
Rochette C,
Bayne MA,
Abramovitz M,
Adam M,
and
Metters KM.
Cloning and expression of a cDNA for the human prostaglandin E receptor EP1 subtype.
J Biol Chem
268:
26767-26772,
1993[Abstract/Free Full Text].
12.
Ichikawa, A,
Sugimoto Y,
and
Negishi M.
Molecular aspects of the structures and functions of the prostaglandin E receptors.
J Lipid Mediat Cell Signal
14:
83-87,
1996[ISI][Medline].
13.
Kachintorn, U,
Vajanaphanich M,
Traynor-Kaplan AE,
Dharmsathaphorn K,
and
Barrett KE.
Activation by calcium alone of chloride secretion in T84 epithelial cells.
Br J Pharmacol
109:
510-517,
1993[Abstract].
14.
Meszaros, JG,
Gonzalez AM,
Endo-Mochizuki Y,
Villegas S,
Villarreal F,
and
Brunton LL.
Identification of G protein-coupled signaling pathways in cardiac fibroblasts: cross talk between Gq and Gs.
Am J Physiol Cell Physiol
278:
C154-C162,
2000[Abstract/Free Full Text].
15.
Morimoto, K,
Sugimoto Y,
Katsuyama M,
Oida H,
Tsuboi K,
Kishi K,
Kinoshita Y,
Negishi M,
Chiba T,
Narumiya S,
and
Ichikawa A.
Cellular localization of mRNAs for prostaglandin E receptor subtypes in mouse gastrointestinal tract.
Am J Physiol Gastrointest Liver Physiol
272:
G681-G687,
1997[Abstract/Free Full Text].
16.
Namba, T,
Sugimoto Y,
Negishi M,
Irie A,
Ushikubi F,
Kakizuka A,
Ito S,
Ichikawa A,
and
Narumiya S.
Alternative splicing of C-terminal tail of prostaglandin E receptor subtype EP3 determines G-protein specificity.
Nature
365:
166-170,
1993[ISI][Medline].
17.
Narumiya, S,
Hirata N,
Namba T,
Hayashi Y,
Ushikubi F,
Sugimoto Y,
Negishi M,
and
Ichikawa A.
Structure and function of prostanoid receptors.
J Lipid Mediators
6:
155-161,
1993[ISI][Medline].
18.
Negishi, M,
Harazono A,
Sugimoto Y,
Hazato A,
Kurozumi S,
and
Ichikawa A.
TEI-3356, a highly selective agonist for the prostaglandin EP3 receptor.
Prostaglandins
48:
275-283,
1994[Medline].
19.
Negishi, M,
Sugimoto Y,
Hayashi Y,
Namba T,
Honda A,
Watabe A,
Narumiya S,
and
Ichikawa A.
Functional interaction of prostaglandin E receptor EP3 subtype with guanine nucleotide-binding proteins, showing low-affinity ligand binding.
Biochim Biophys Acta
1175:
343-350,
1993[ISI][Medline].
20.
Parrott, RF,
and
Vellucci SV.
Effects of centrally administered prostaglandin EP receptor agonists on febrile and adrenocortical responses in the prepubertal pig.
Brain Res Bull
41:
97-103,
1996[ISI][Medline].
21.
Reimer, R,
Heim HK,
Muallem R,
Odes HS,
and
Sewing KF.
Effects of EP-receptor subtype specific agonists and other prostanoids on adenylate cyclase activity of duodenal epithelial cells.
Prostaglandins
44:
485-493,
1992[Medline].
22.
Sakai, H,
Kumano E,
Ikari S,
and
Takeguchi N.
A gastric housekeeping Cl
channel activated via prostaglandin EP3 receptor-mediated Ca2+/nitric oxide/cGMP pathway.
J Biol Chem
270:
18781-18785,
1995[Abstract/Free Full Text].
23.
Selbie, LA,
and
Hill SJ.
G protein-coupled-receptor cross-talk: the fine-tuning of multiple receptor-signaling pathways.
Trends Pharmacol Sci
19:
87-93,
1998[ISI][Medline].
24.
Sugimoto, Y,
Negishi M,
Hayashi Y,
Namba T,
Honda A,
Watabe A,
Hirata M,
Narumiya S,
and
Ichikawa A.
Two isoforms of the EP3 receptor with different carboxyl-terminal domains. Identical ligand binding properties and different coupling properties with Gi proteins.
J Biol Chem
268:
2712-2718,
1993[Abstract/Free Full Text].
25.
Takafuji, V,
Lublin D,
Cosme R,
Lynch K,
and
Roche JK.
Prostanoids in normal and inflamed colonic mucosa: localization of cell-specific prostanoid receptors and enzymes for synthesis (Abstract).
Gastroenterology
116:
A922,
1999[ISI].
26.
Takeuchi, K,
Ukawa H,
Kato S,
Furukawa O,
Araki H,
Sugimoto Y,
Ichikawa A,
Ushikubi F,
and
Narumiya S.
Impaired duodenal bicarbonate secretion and mucosal integrity in mice lacking prostaglandin E-receptor subtype EP(3).
Gastroenterology
117:
1128-1135,
1999[ISI][Medline].
27.
Takeuchi, K,
Yagi K,
Kato S,
and
Ukawa H.
Roles of prostaglandin E-receptor subtypes in gastric and duodenal bicarbonate secretion in rats.
Gastroenterology
113:
1553-1559,
1997[ISI][Medline].
28.
Vajanaphanich, M,
Schultz C,
Tsien RY,
Traynor-Kaplan AE,
Pandol SJ,
and
Barrett KE.
Cross-talk between calcium and cAMP-dependent intracellular signaling pathways. Implications for synergistic secretion in T84 colonic epithelial cells and rat pancreatic acinar cells.
J Clin Invest
96:
386-393,
1995[ISI][Medline].
29.
Watabe, A,
Sugimoto Y,
Honda A,
Irie A,
Namba T,
Negishi M,
Ito S,
Narumiya S,
and
Ichikawa A.
Cloning and expression of cDNA for a mouse EP1 subtype of prostaglandin E receptor.
J Biol Chem
268:
20175-20178,
1993[Abstract/Free Full Text].
Am J Physiol Gastrointest Liver Physiol 281(2):G375-G381
0193-1857/01 $5.00
Copyright © 2001 the American Physiological Society