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
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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 Omega  · 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
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

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 beta 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 beta gamma -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
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
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