Using the Beck Depression Inventory to Assess Anhedonia: A Scale Validation Study.

Anhedonia is central to several psychological disorders and a frequent target of psychosocial and pharmacological treatments. We evaluated the psychometric properties of two widely used anhedonia measures derived from the Beck Depression Inventory: a 3-item (BDI-Anh3) and a 4-item version (BDI-Anh4). We evaluated these measures in a large undergraduate sample, a community sample, and a clinical sample. Both the BDI-Anh3 and the BDI-Anh4 showed adequate internal consistency, with BDI-Anh4 performing somewhat better, across the three samples. Both measures showed good convergent and discriminant validity, even after controlling for shared variance with other items on the BDI. These findings indicate that both measures have sufficient reliability and validity to support their use by researchers and clinicians.

How do fluctuating ecological dynamics impact the evolution of hosts and parasites?

Theoretical models of the evolution of parasites and their hosts have shaped our understanding of infectious disease dynamics for over 40 years. Many theoretical models assume that the underlying ecological dynamics are at equilibrium or constant, yet we know that in a great many systems there are fluctuations in the ecological dynamics owing to a variety of intrinsic or extrinsic factors. Here, we discuss the challenges presented when modelling evolution in systems with fluctuating ecological dynamics and summarize the main approaches that have been developed to study host-parasite evolution in such systems. We provide an in-depth guide to one of the methods by applying it to two worked examples of host evolution that have not previously been studied in the literature: when cycles occur owing to seasonal forcing in competition, and when the presence of a free-living parasite causes cycles, with accompanying interactive Python code provided. We review the findings of studies that have explored host-parasite evolution when ecological dynamics fluctuate, and point to areas of future research. Throughout we stress the importance of feedbacks between the ecological and evolutionary dynamics in driving the outcomes of infectious disease systems. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Diversity and the maintenance of sex by parasites.

The Red Queen hypothesis (RQH) predicts that parasite-mediated selection will maintain sexual individuals in the face of competition from asexual lineages. The prediction is that sexual individuals will be difficult targets for coevolving parasites if they give rise to more genetically diverse offspring than asexual lineages. However, increasing host genetic diversity is known to suppress parasite spread, which could provide a short-term advantage to clonal lineages and lead to the extinction of sex. We test these ideas using a stochastic individual-based model. We find that if parasites are readily transmissible, then sex is most likely to be maintained when host diversity is high, in agreement with the RQH. If transmission rates are lower, however, we find that sexual populations are most likely to persist for intermediate levels of diversity. Our findings thus highlight the importance of genetic diversity and its impact on epidemiological dynamics for the maintenance of sex by parasites.

Epigonal conditioned media from bonnethead shark, Sphyrna tiburo, induces apoptosis in a T-cell leukemia cell line, Jurkat E6-1.

Representatives of Subclass Elasmobranchii are cartilaginous fish whose members include sharks, skates, and rays. Because of their unique phylogenetic position of being the most primitive group of vertebrates to possess all the components necessary for an adaptive immune system, the immune regulatory compounds they possess may represent the earliest evolutionary forms of novel compounds with the potential for innovative therapeutic applications. Conditioned medium, generated from short term culture of cells from the epigonal organ of bonnethead sharks (Sphyrna tiburo), has been shown to have potent reproducible cytotoxic activity against a variety of human tumor cell lines in vitro. Existing data suggest that epigonal conditioned medium (ECM) exerts this cytotoxic activity through induction of apoptosis in target cells. This manuscript describes apoptosis induction in a representative tumor cell line, Jurkat E6-1, in response to treatment with ECM at concentrations of 1 and 2 mg/mL. Data indicate that ECM exposure initiates the mitochondrial pathway of apoptosis through activation of caspase enzymes. Future purification of ECM components may result in the isolation of an immune-regulatory compound with potential therapeutic benefit for treatment of human cancer.

Contribution of the P2Y12 receptor-mediated pathway to platelet hyperreactivity in hypercholesterolemia.

BACKGROUND: In hypercholesterolemia, platelets demonstrate increased reactivity and promote the development of cardiovascular disease. OBJECTIVE: This study was carried out to investigate the contribution of the ADP receptor P2Y12-mediated pathway to platelet hyperreactivity due to hypercholesterolemia. METHODS: Low-density lipoprotein receptor-deficient mice and C57Bl/6 wild-type mice were fed on normal chow and high-fat (Western or Paigen) diets for 8 weeks to generate differently elevated cholesterol levels. P2Y12 receptor-induced functional responses via G(i) signaling were studied ex vivo when washed murine platelets were activated by 2MeSADP and PAR4 agonist AYPGKF in the presence and absence of indomethacin. Platelet aggregation and secretion, α(IIb)ß(3) receptor activation and the phosphorylation of extracellular signal-regulated protein kinase (ERK) and Akt were analyzed. RESULTS: Plasma cholesterol levels ranged from 69 ± 10 to 1011 ± 185 mg dL(-1) depending on diet in mice with different genotypes. Agonist-dependent aggregation, dense and α-granule secretion and JON/A binding were gradually and significantly (P < 0.05) augmented at low agonist concentration in correlation with the increasing plasma cholesterol levels, even if elevated thromboxane generation was blocked. These functional responses were induced via increased levels of G(i) -mediated ERK and Akt phosphorylation in hypercholesterolemic mice vs. normocholesterolemic animals. In addition, blocking of the P2Y12 receptor by AR-C69931MX (Cangrelor) resulted in strongly reduced platelet aggregation in mice with elevated cholesterol levels compared with normocholesterolemic controls. CONCLUSIONS: These data revealed that the P2Y12 receptor pathway was substantially involved in platelet hyperreactivity associated with mild and severe hypercholesterolemia.

In vivo exposure of clearnose skates, Raja eglanteria, to ionising X-radiation: acute effects on the peripheral blood, spleen, and epigonal and Leydig organs.

The effects of ionising radiation on the peripheral blood, spleen, and epigonal and Leydig organs of cartilaginous fishes were investigated using juvenile clearnose skates, Raja eglanteria. Skates (N = 80) were sacrificed 12 days after exposure to 0-75 Gy of X-radiation, and morphometrics (body mass, disc width, total length), mass of spleens and epigonal organs, and peripheral blood leucocyte (PBL) counts were compared to controls using ANOVA. Spleen and epigonal organ mass and PBL counts declined logarithmically as a function of radiation dose. To assess recovery from X-radiation, skates (N = 40) were exposed to 0, 9 or 18 Gy and sacrificed when moribund or on days 10, 20, 30 and 40 post-irradiation. Partial recovery of Leydig organ and splenic red pulp was evident after 40 days in skates exposed to 9 Gy, but no indication of recovery was apparent at higher doses. Median lethal dose by 30 days (LD50/30) was calculated to be 9-18 Gy, similar to that determined for other fishes.

Nitric oxide production by nurse shark (Ginglymostoma cirratum) and clearnose skate (Raja eglanteria) peripheral blood leucocytes.

Reactive nitrogen intermediates, such as nitric oxide (NO), are important immunomodulators in vertebrate immune systems, but have yet to be identified as mediators of host defence in any member of class Chondrichthyes, the cartilaginous fishes. In the present study, production of NO by nurse shark (Ginglymostoma cirratum) peripheral blood leucocytes (PBL) stimulated with bacterial cell wall lipopolysaccharide (LPS) was investigated. PBL were cultured for 24 to 96 h following stimulation with LPS at concentrations ranging from 0 to 25 microg ml(-1), in both serum-supplemented and serum-free culture conditions. Production of NO was measured indirectly using the Griess reaction, with maximal NO production occurring after 72 h using 10% FBS and 10 microg LPS ml(-1). Application of these culture conditions to PBL from another cartilaginous fish (clearnose skate, Raja eglanteria) resulted in a similar NO response. Addition of a specific inhibitor of inducible nitric oxide synthase (iNOS), L-N(6)-(1-iminoethyl)lysine (L-NIL), resulted in a significant decrease in the production of NO by PBL from both species.

In vivo exposure of clearnose skates, Raja eglanteria, to ionizing X-radiation: acute effects on the thymus.

To investigate for the first time the effects of ionizing radiation on thymus of a representative cartilaginous fish, juvenile clearnose skates, Raja eglanteria, were exposed to 0-75 Gy of X-radiation and sacrificed after 12 days. Morphometrics (weight, disc width and total length) and thymus and thymic cyst area were compared to controls using ANOVA. Thymus area declined logarithmically and medullary cysts increased as a function of dose (P < or = 0.05). To assess thymic recovery, skates were exposed to 0, 9, 13.5 or 18 Gy of X-radiation and sacrificed when moribund or on days 10, 20, 30 and 40 post-irradiation. Complete restoration of the thymus was not achieved during the 40-day observation period, although repopulation with pro-thymocytes and partial recovery of thymic architecture were evident histologically. The observed high radiosensitivity of R. eglanteria thymocytes was similar to responses of other vertebrates, but recovery time was prolonged.

Lateral tunnel versus extracardiac conduit Fontan procedure: a concurrent comparison.

BACKGROUND: The aim of this study was to compare the outcomes of the lateral tunnel (LT) and extracardiac conduit (ECC) Fontan procedures at a single institution over the same time period. METHODS: From November 1995 through October 2002, 70 Fontan procedures were performed: 37 LT and 33 ECC. All were fenestrated; 96% were staged with a prior superior cavopulmonary connection. Compared with the ECC patients, the LT patients were younger (2.7 +/- 1.1 vs 3.9 +/- 2.5 years; p = 0.01), had a higher incidence of hypoplastic left heart syndrome (57% vs 21%; p < 0.01), and a longer aortic cross-clamp time (55 +/- 13 vs 26 +/- 15 min; p < 0.01). Weight, gender, preoperative cardiac catheterization values, and cardiopulmonary bypass time did not differ between the two groups. RESULTS: Operative mortality was 2.8%, 1 patient in each group (p = 1.0). Over the first 24 hours following operation the mean Fontan pressure, transpulmonary gradient, and common atrial pressure did not differ between LT and ECC patients. The median duration of mechanical ventilation (LT 12 vs ECC 18 hours), intensive care unit stay (LT 2 vs ECC 3 days), chest tube drainage (LT 10 vs ECC 8 days), and hospital stay (LT 11 vs ECC 12 days) did not differ. The ECC patients had a higher incidence of sinus node dysfunction both in the postoperative period (27% vs LT 8%; p = 0.09), and persisting at hospital discharge (10% vs LT 0%; p = 0.02). Mean follow-up was 3.6 +/- 1.6 years in LT, and 3.0 +/- 2.2 years in ECC patients (p = 0.2). There was one late death. Actuarial survival at 5 years is 97% for LT, and 91% for ECC patients (p = 0.4); 96% of patients are in NYHA class I, and 4% in class II, with no difference between groups. Sinus node dysfunction was seen during follow-up in 15% LT vs 28% ECC patients (p = 0.2). CONCLUSIONS: The LT and ECC approaches had comparable early and mid-term outcomes, including operative morbidity and mortality, postoperative hemodynamics, resource use, and mid-term survival and functional status. ECC patients had a higher incidence of sinus node dysfunction early after operation.

Agonist-induced internalization and mitogen-activated protein kinase activation of the human prostaglandin EP4 receptor.

We examined the pathway of prostaglandin E(2) (PGE(2))-induced internalization of the prostaglandin EP4 receptor in HEK 293 cells. Co-expression of dominant negative beta-arrestin (319-418) or dynamin I (K44A) with the EP4 receptor reduced internalization. The activated receptor co-localized with GFP-arrestin 2 and GFP-arrestin 3, confirming the requirement for beta-arrestins in internalization. Inhibition of clathrin-coated vesicle-mediated internalization resulted in inhibition of sequestration, whereas inhibition of caveola-mediated internalization had no effect. PGE(2) stimulation of the EP4 receptor resulted in rapid mitogen-activated protein (MAP) kinase activation. Examination of an internalization-resistant mutant and co-expression of mutant accessory proteins with EP4 revealed that MAP kinase activation proceeds independently of internalization.

Patterns of cyclic AMP formation by coexpressed D1 and D2L dopamine receptors in HEK 293 cells.

Recent studies using immunofluorescence confocal microscopy (Aizman et al., Nature neuroscience (2000) 3, 226-230) present compelling evidence for colocalization of D1 and D2 dopamine receptors on neurons in the striatum and nucleus accumbens. To examine some of the biochemical consequences of colocalization we coexpressed the D1 and D2 dopamine receptors in HEK293 cells. Dopamine D1 and D2 receptors couple to stimulation and inhibition of adenylyl cyclase, respectively. In cells expressing only the D1 receptor, dopamine stimulated cAMP formation with an EC50 of 2.15 nM. In cells expressing only the D2L receptor, dopamine inhibited cAMP formation by 80% with an EC50 of 0.02 nM. The effect of dopamine on the D2L receptor was antagonized by the selective antagonist spiperone with an IC50 of 0.31 nM. In cells coexpressing both the D1 and D2L receptors, dopamine caused an increase in cAMP that was only 20% of that observed with the D1 receptor alone. In this case, increasing concentrations of spiperone caused a change in the dose-response curve from hyperbolic to bell-shaped as the concentration of spiperone was increased. Using pharmacological constants determined from studies on the individually expressed receptors, the curves obtained in cells co-expressing the two receptors could be modeled by kinetic expressions derived by summing the contributions from each receptor. The model leads to a re-interpretation of the pharmacology of dopaminergic ligands. Hence, one consequence of colocalization is that D2 receptor antagonists become functional agonists of cAMP formation.

Determination of D1 and D2 dopamine receptor expression by Ntera-2 cells.

There is evidence that D1 and D2 dopamine receptors are co-expressed on some neurons. As a potential model of co-expression we examined Ntera-2 cells using RT-PCR, and showed that they express D2 but not D1 receptors. D2 dopamine receptor expression was confirmed by quinpirole inhibition of forskolin-stimulated cAMP formation. Absence of D1 dopamine receptors was confirmed by the inability of dopamine or SKF 81297 to increase cAMP.

Comparison of agonist-induced internalization of the human EP2 and EP4 prostaglandin receptors: role of the carboxyl terminus in EP4 receptor sequestration.

Prostaglandin E(2) (PGE(2)) couples to stimulation of adenylyl cyclase through two distinct G protein-coupled receptors designated EP2 and EP4. Although they have similar affinities for PGE(2), the EP(2) and EP4 receptors have distinct structural characteristics. EP2 is a 358-amino-acid protein with short third intracellular loop and C-terminal domains, whereas EP4 consists of 488 amino acids with a long third intracellular loop and a long cytoplasmic tail. The ability of the HA epitope-tagged receptors to undergo PGE(2)-induced internalization was examined by enzyme-linked immunosorbent assay and immunofluorescence microscopy after expression in human embryonic kidney 293 cells. The EP2 receptor did not internalize, whereas the EP4 receptor underwent rapid internalization. Truncation of the EP4 receptor after amino acid 350, which removes 138 residues, abolished internalization. Truncation after amino acid 369 markedly attenuated internalization, whereas truncation after amino acid 383 had little effect. Serine and threonine residues in the region 350 to 383 were mutated to determine their role in internalization. The mutants S370-382A, a full-length receptor containing six serine-to-alanine mutations in the region 370 to 382, and S354-369A, containing four serine mutations and one threonine mutation in the region 350 to 370, both internalized to the same extent as the wild-type. A further mutant, designated S354-382A, containing amino acid substitutions S354A, S359A, S364A, S366G, T369A, S370A, S371A, S374A, S377A, S379A, and S382A, also internalized to the same extent as the wild-type. We conclude that the C terminus of the EP4 receptor is involved in internalization; however, serine and threonine residues do not seem to be involved.

Identification of a region of the C-terminal domain involved in short-term desensitization of the prostaglandin EP4 receptor.

1. The prostaglandin EP4 receptor, which couples to stimulation of adenylyl cyclase, undergoes rapid agonist-induced desensitization when expressed in CHO-K1 cells. 2. Truncation of the 488-amino acid receptor at residue 350 removes the carboxy-terminal domain and abolishes desensitization. 3. To further delineate residues involved in desensitization, the receptor was truncated at position 408, 383 or 369. Receptors truncated at position 408 or 383 underwent PGE2-induced desensitization, whereas the receptor truncated at position 369 displayed sustained activity, indicating that the essential residues for desensitization lie between 370 and 383. 4. The six serines in the 14-amino acid segment between residues 370 and 383 were mutated to alanine, retaining the entire C-terminal domain. Desensitization was absent in cells expressing this mutant. 5. The results indicate involvement of serines located between 370 and 382 in rapid desensitization of the EP4 receptor.

Distribution of prostaglandin IP and EP receptor subtypes and isoforms in platelets and human umbilical artery smooth muscle cells.

Prostaglandins act through specific receptors to stimulate cyclic AMP formation which inhibits platelet activation and relaxes vascular smooth muscle. We have used RT-PCR combined with Southern blot analysis to determine the subtypes of prostaglandin receptor on platelets. Platelets expressed the EP4 rather than the EP2 prostaglandin EP receptor subtype, whereas vascular smooth muscle cells predominantly expressed the EP2 receptor. The IP receptor, which binds prostacyclin and couples to stimulation of adenylyl cyclase, and three isoforms of the inhibitory EP3 receptor were equally expressed in platelets, HEL cells and umbilical artery smooth muscle cells. The EP3-II isoform showed variation in level of expression among the three cell types. As a positive control for the presence of platelet RNA, PCR was performed using primers specific for the alpha chain of the platelet membrane glycoprotein Ib. As a negative control for the absence of T and B cell contamination in the platelet RNA, PCR was performed using primers specific for the cell specific cluster determinants CD2 (a T-cell marker) and CD20 (a B-cell marker). The finding that platelets express both stimulatory and inhibitory prostaglandin receptors provides confirmation of a homeostatic model of regulation of platelet adenylyl cyclase previously proposed.

Agonist-induced desensitization and down-regulation of the human kappa opioid receptor expressed in Chinese hamster ovary cells.

In this study, we examined whether the human kappa opioid receptor stably expressed in Chinese hamster ovary cells underwent desensitization and down-regulation after prolonged exposure to the agonist (-)U50,488H. Pretreatment with (-)U50,488H led to a reduction in the magnitude of increase in [35S]GTPgammaS binding by the subsequent application of (-)U50,488H. The extent of desensitization was related to duration of exposure and (-)U50,488H concentration. Pretreatment with (-)U50,488H also reduced the potency of (-)U50,488H in inhibiting forskolin-stimulated adenylate cyclase. In membranes of (-)U50,488H-pretreated cells, the affinity of (-)U50,488H was lower than that in the untreated control, and GTPgammaS had no effect on (-)U50,488H affinity, consistent with the notion of uncoupling of the receptor-G protein complex by (-)U50, 488H treatment. Down-regulation of the kappa opioid receptor also occurred on exposure to (-)U50,488H. Higher (-)U50,488H concentrations and/or longer incubation periods were required for down-regulation than for desensitization. The degree of down-regulation depended on the agonist concentration and incubation time. (-)U50,488H-induced desensitization and down-regulation were blocked by naloxone. (+)U50,488H, an inactive stereoisomer, did not cause desensitization or down-regulation. These results indicate that both processes were receptor-mediated. After incubation with (-)U50,488H and removal of (-)U50,488H, both (-)U50,488H-induced [35S]GTPgammaS binding and receptor number returned to the control level, which indicates that both processes were reversible. Thus, desensitization and down-regulation of the kappa opioid receptor occur after agonist exposure and represent two different adaptation mechanisms.

Co-expression of prostaglandin receptors with opposite effects: a model for homeostatic control of autocrine and paracrine signaling.

Prostaglandins are ubiquitous autocrine mediators that exert their effects through a number of G protein-coupled receptors. Many organs and tissues express many of the prostaglandin receptors, and prostaglandins have diverse effects on individual organs and tissues. In some cases, several prostaglandin receptors are expressed on a single cell type. Co-expressed prostaglandin receptors frequently appear to have opposite actions, suggesting homeostatic control of prostaglandin effects. Co-expression of opposing receptors provides a molecular mechanism for weak or partial agonism and explains the action of a drug as a mixed agonist/antagonist. The physiological relevance of co-expressed opposing receptors for a single agonist perhaps can be explained in terms of the difference between endocrine and autocrine mediators. Endocrine hormones are generally produced by cells distant from their site of action so that they are diluted to an elevated but stable concentration by the time they reach their target cells. In contrast, autocoids are produced by the same cell type on which they act and may reach transiently high levels at their sites of action. The presence of a second type of receptor that negates the action of the first receptor would tend to buffer cellular responses to transient extremes of agonist concentration. The slow onset of inhibition would also allow for time-dependent buffering, providing additional control over autocoid release and effect. The mechanism is relevant to other autocrine and paracrine mediators including neurotransmitters, which reach transiently high concentrations in the synaptic cleft.

Molecular basis for ADP-induced platelet activation. I. Evidence for three distinct ADP receptors on human platelets.

Acting through cell surface receptors, ADP activates platelets resulting in shape change, aggregation, thromboxane A2 production, and release of granule contents. ADP also causes a number of intracellular events including inhibition of adenylyl cyclase, mobilization of calcium from intracellular stores, and rapid calcium influx in platelets. However, the receptors that transduce these events remain unidentified and their molecular mechanisms of action have not been elucidated. The receptor responsible for the actions of ADP on platelets has been designated the P2T receptor. In this study we have used ARL 66096, a potent antagonist of ADP-induced platelet aggregation, and a P2X ionotropic receptor agonist, alpha,beta-methylene adenosine 5'-triphosphate, to distinguish the ADP-induced intracellular events. ARL 66096 blocked ADP-induced inhibition of adenylyl cyclase, but did not affect ADP-mediated intracellular calcium increases or shape change. Both ADP and 2-methylthio-ADP caused a 3-fold increase in the level of inositol 1,4,5-trisphosphate over control levels which peaked in a similar fashion to the Ca2+ transient. The increase in inositol 1,3,4-trisphosphate was of similar magnitude to that of inositol 1,4,5-trisphosphate. alpha,beta-Methylene adenosine 5'-triphosphate did not cause an increase in either of the inositol trisphosphates. These results clearly demonstrate the presence of two distinct platelet ADP receptors in addition to the P2X receptor: one coupled to adenylyl cyclase and the other coupled to mobilization of calcium from intracellular stores through inositol trisphosphates.

Constitutive activity of human prostaglandin E receptor EP3 isoforms.

1. The human EP3 prostaglandin receptor is a seven transmembrane, G protein-coupled receptor that couples to inhibition of adenylyl cyclase. The receptor occurs as at least six isoforms which result from alternative splicing. The isoforms are identical over the first 359 amino acids, comprising the seven transmembrane helices, but differ in the carboxyl terminal tail which ranges in length from 6 to 65 amino acids beyond the common region. 2. We have stably expressed in CHO-K1 cells four of the isoforms (EP3I-EP3IV) and a form of the EP3 receptor (T-359) truncated at the carboxyl-terminal region defined by the alternative splicing site at amino acid number 359. 3. Isoforms EP3I and EP3II showed concentration-dependent inhibition of forskolin-stimulated adenylyl cyclase in CHO-K1 cells by the EP3 receptor agonist, sulprostone. The IC50 calculated for sulprostone inhibition was 0.2 nM for EP3I and 0.15 nM for EP3II. The maximum extent of inhibition was 80% for both isoforms. 4. Isoforms EP3III and EP3IV showed marked constitutive activity, inhibiting forskolin-stimulated adenylyl cyclase in the absence of agonist. EP3IV also displayed some agonist-dependent inhibition whereas EP3III was fully constitutively active. 5. The truncated receptor T-359 was fully constitutively active, inhibiting forskolin-stimulated adenylyl cyclase by about 70% in the absence of agonist, and showed no agonist-dependent inhibition, in agreement with a similar truncation of the mouse EP3 receptor. 6. To confirm that differences in cyclic AMP level between isoforms represent constitutive activity, we treated cells with pertussis toxin for 6 h to abolish Gi function. Pertussis toxin reversed sulprostone-mediated inhibition of cyclic AMP formation in EP3I and EP3II and abolished constitutive activity of EP3III, EP3IV and T-359 so that the level of forskolin-stimulated cyclic AMP produced was the same in all cells and similar to that obtained in mock-transfected cells. In mock-transfected cells, sulprostone had no effect on forskolin-stimulated cyclic AMP formation. 7. For these experiments we chose clones that showed similar expression levels of each isoform, as determined by binding of [3H]-prostaglandin E2 (PGE2) (EP3I, 0.71; EP3II, 1.47; EP3IV, 1.59 pmol mg-1 protein). Mock-transfected cells showed no detectable binding of [3H]-PGE2. In addition, we performed a detailed study of the effects of expression level on constitutive activity. Over a six fold range of expression there was no change in the properties of each isoform with regard to whether it was constitutively active or not. 8. The degree of constitutive activity correlated with the inverse of the length of the C-terminal tail of the isoforms. However, no correlation was found between isoforms from human and mouse: whereas EP3II shows no constitutive activity, its mouse homologue, EP3 gamma, shows almost complete constitutive activity, even though the C-terminal domains of the receptors following the splice site differ in only 7 of 29 amino acids.