Genetic analysis of protein kinase B (AKT) in Drosophila

The decision between survival and death is an important aspect of cellular regulation during development and malignancy. Central to this regulation is the process of apoptosis, which is conserved in multicellular organisms [1]. A variety of signalling cascades have been implicated in modulation of apoptosis, including the phosphatidylinositol (Pl) 3-kinase pathway. Activation of Pl 3-kinase is protective, and inhibition of this lipid kinase enhances cell death under several conditions including deregulated expression of c-Myc, neurotrophin withdrawal and anoikis [2-7]. Recently, the protective effects of Pl 3-kinase have been linked to its activation of the pleckstrin homology (PH)-domain-containing protein kinase B (PKB or AKT) [8]. PKB/AKT was identified from an oncogene, v-akt, found in a rodent T-cell lymphoma [9]. To initiate a genetic analysis of PKB, we have isolated and characterized a Drosophila PKB/AKT mutant (termed Dakt1) that exhibits ectopic apoptosis during embryogenesis as judged by induction of membrane blebbing, DNA fragmentation and macrophage infiltration. Apoptosis caused by loss of Dakt function is rescued by caspase suppression but is distinct from the previously described reaper/grim/hid functions. These data implicate Dakt1 as a cell survival gene in Drosophila, consistent with cell protection studies in mammals.

Immunohistochemical study of protein kinase C in the testes of cattle and pigs

We investigated the expression of novel protein kinase C (PKC) delta and theta in the testes of pigs and cattle using Western blot and immunohistochemical analysis. PKC delta and theta are recognized in the testes of pigs and cattle by Western blot analysis. We found in immunohistochemical study that PCK delta was localized in the spermatids of seminiferous tubules, but not in the interstitial cells, while PKC theta was recognized only in the interstitial cells of the testes of in both species. These findings suggest that PKC delta and theta play an important role in the development of spermatozoa and the regulation of androgen in the testicular interstitial cells (probably Leydig cells), respectively.

C-fos mediates cocaine inhibition of NGF-induced PC12 cell differentiation

In utero cocaine exposure can affect CNS development. Previous studies showed that cocaine inhibits neuronal differentiation in a dose-dependent fashion, in nerve growth factor (NGF)-stimulated PC12 cells, without affecting cell viability. NGF activates intracellular signaling proteins, specific immediate-early genes (IEG) including a transient peak of c-fos expression, and induction of late genes expression, leading to the neuronal phenotype. We hypothesized that cocaine interferes with NGF signaling. Therefore, we examined the pattern of c-fos expression in our cellular model. Time course of c-fos expression up to 72 h was determined in cells treated with NGF 20 ng/ml and cocaine 10 microgram/ml (a moderately toxic level) by RT-PCR analysis. Total RNA was isolated from cells, and levels of c-fos mRNA were estimated using gene-specific primers. In both control and experimental conditions, c-fos level was maximal at 0.5 h. In the control cells, c-fos expression declined rapidly to less than 5% of the 0.5h value, while in the cocaine-treated cells, c-fos level persisted through the 72-h exposure. Adding c-fos antisense to cells treated with NGF and cocaine resulted in significant improvement of neurite out-growth, from 28% (NGF + cocaine) to 89% (NGF + cocaine + c-fos antisense) of control differentiation after 72 h of exposure (Dunnet's T < 3.24). Inhibitory effects of cocaine on NGF-induced PC12 differentiation may be attributed to alteration of c-fos expression. Further studies will be required to examine the role of D1 receptor activation in mediating c-fos expression and to explore the effects of cocaine on other IEGs.

Distribution of P2Y receptor subtypes on haematopoietic cells

1. RT-PCR-southern hybridization analyses with radiolabelled P2Y receptor cDNAs as probes indicated that the peripheral blood leukocytes and the human umbilical vein endothelial cells express P2Y1, P2Y2, P2Y4 and P2Y6 receptors. 2. Of the haematopoietic cell lines tested, promonocytic U937 cells express P2Y2 and P2Y6, but not P2Y1 or P2Y4; promyelocytic HL-60 cells express the P2Y1, P2Y2 and P2Y6 receptors but not the P2Y4 receptor; K562 cells express P2Y1 but not P2Y2, P2Y4 or P2Y6; and Dami cells express P2Y1, P2Y2, P2Y4 and P2Y6 receptors. 3. Of the peripheral blood leukocytes tested, polymorphonuclear cells express P2Y4 and P2Y6 but not P2Y1 or P2Y2 receptors; monocytes express P2Y1, P2Y2, P2Y4 and P2Y6 receptors and lymphocytes express P2Y1, P2Y2, P2Y4 and P2Y6 receptors. 4. These results suggest a physiological role for different P2Y receptor subtypes in the extracellular nucleotide-mediated stimulation of monocytes, neutrophils, lymphocytes and endothelial cells.

[The morphological and functional changes of pulmonary intravascular macrophages induced by LPS]

OBJECTIVE

To study the roles of pulmonary intravascular macrophages (PIMs) on infective acute lung injury (ALI).

METHOD

Porcine pulmonary blood vessels were flushed by modified Morton's method, PIMs were isolated by adhesion method and identified with the features at both light and electron microscopic level. The activity of IL-1 beta, and content of IL-6, IL-8 and TNF alpha in the culture supernatants were measured by thymocyte proliferation or ELISA, respectively.

RESULT

Enlarged and increased pseudopods, and increased amount of lysosomes and phagosomes were found in the PIM stimulated with lipopolysaccharide (LPS, 10 micrograms/ml); the releases of TNF alpha, IL-1 beta, IL-6 and IL-8 were increased significantly as compared with the level of pre-stimulation of LPS (P < 0.01), and reaching their peaks at 1 h, 2 h, 4 h and 6 h after LPS stimulation, respectively.

CONCLUSION

The isolation of porcine PIMs can be completed with modified Morton's method; the phagocytosis and secretion of PIMs are more active after LPS stimulation. In the pathogenesis of ALI, TNF alpha and IL-1 beta may play an important role at its early stage; however, the IL-6 and IL-8 may be associated with the pathophysiological changes at the later stage of ALI.

Enhancement of (-)-stepholidine on protein phosphorylation of a dopamine- and cAMP-regulated phosphoprotein in denervated striatum of oxidopamine-lesioned rats

AIM

To study effects of (-)-stepholidine (SPD) on the phosphorylation of a dopamine- and cAMP-regulated phosphoprotein (DARPP-32) in the striatum of oxidopamine-lesioned rats.

METHODS

The amount of dephospho-DARPP-32 was measured by a back-phosphorylation assay.

RESULTS

In the striatum of control rats, SPD per se had no effect on the phosphorylation of DARPP-32, but it antagonized the decrease by 28% of dephospho-DARPP-32 induced by the D1 agonist SK&F-38393. In the denervated striatum of oxidopamine-lesioned rats, SPD decreased the amount of dephospho-DARPP-32 by 44%. The effect of SPD was completely counteracted by the concomitant administration of the D1 antagonist Sch-23390.

CONCLUSION

SPD exhibits D1 agonistic action on DARPP-32 phosphorylation in the denervated striatum of oxidopamine-lesioned rats, but it acts as a D1 antagonist in normal striatum.

Three-dimensional modeling for modern diagnosis and planning in maxillofacial surgery

The existing methods of recording the face in three dimensions are reviewed, and a new method for three-dimensional facial modeling is introduced. The technique utilizes two stereo pairs of videocameras, a stereo pair at each side of the patient's face. The system allows rapid capture of the face in three dimensions and precise measurement of anatomic landmarks. The system can be used to capture the facial image and a cephalogram almost simultaneously, allowing more accurate superimposition of soft and hard tissues. This precision will facilitate development of the surgical treatment plan. A computer program in the early stages of development will use the data generated by this biostereometric measurement system to predict soft tissue changes following orthognathic surgery.

A three-dimensional imaging system for archiving dental study casts: a preliminary report

Dental study casts form an essential part of patient records for both diagnostic and medicolegal purposes. Storage of study casts poses major problems because of inconvenience and cost of mass storage. Various methods for recording and storage of study casts are discussed. A new biostereometric technique for digitally recording and storing dental casts, and using the recent advances in stereophotogrammetry, is presented. Archiving dental casts in a digital format would reduce problems of mass storage and provide new benefits such as duplication of casts and use in clinical and research studies.

Radioimmunoassay of human cardiac acidic isoferritin: a new index for hepatic cancer

OBJECTIVE

To investigate human cardiac acidic isoferritin as a specific index of hepatic cancer.

METHODS

Acidic isoferritin was isolated and purified from human heart muscle. A radioimmunoassay for the acidic isoferritin in human serum has been developed, on the equilibrium method. The antiserum was obtained from rabbits immunized with purified acidic isoferritin. The 125I-acidic isoferritin was prepared by the chloramine-T method. The data were processed using the automated smoothed spline function data processing program.

RESULTS

The intra- and inter-assay CV of acidic isoferritin RIA were 1.65% and 9.71%, respectively, and the recovery rate was 102%. The antiserum provided a linear response from 7.0 to 369.6 micrograms/L with ED50 of 27.50 micrograms/L. The cross reactivity with AFP, CEA, lactoferrin and transferrin was negligible, and that with ferritin was 1.74%. The serum acidic isoferritin concentration showed a considerable variation in different sex and age groups. The serum acidic isoferritin was measured in liver diseases including hepatic cancer, hepatic cirrhosis and acute and chronic hepatitis. Its sensitivity for diagnosis of hepatic cancer was 73.05%, independent from the severity of hepatic injury. In 8 malignant tumors studied, acidic isoferritin appeared the most valuable in the diagnosis of hepatic cancer, with its positive, negative, false positive and false negative rates all being ideal.

CONCLUSIONS

Acidic isoferritin may turn to be a rather specific index of hepatic cancer. Combination of monitoring both acidic isoferritin and AFP would raise the positive detection and specificity in the diagnosis of hepatic cancer.

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.

Molecular basis for ADP-induced platelet activation. II. The P2Y1 receptor mediates ADP-induced intracellular calcium mobilization and shape change in platelets

ADP is an important platelet agonist causing shape change from smooth discoid shape to spiculated spheres and platelet aggregation. However, the molecular mechanisms involved in ADP-induced platelet activation have not been elucidated. We demonstrated earlier the existence of two distinct ADP receptors on platelets, one coupled to phospholipase C, P2TPLC, and the other to inhibition of adenylyl cyclase, P2TAC (Daniel, J. L., Dangelmaier, C., Jin, J., Ashby, B., Smith, J. B., and Kunapuli, S. P. (1998) J. Biol. Chem. 273, 2024-2029), in addition to the previously described P2X1 receptor. Here we report the cloning of a cDNA clone encoding the P2Y1 receptor from a human platelet cDNA library by homology screening with radiolabeled P2Y1-P2Y6 receptor cDNAs. ADP or 2-methyl(thio)-ADP-induced intracellular calcium increases were inhibited by the P2Y1 receptor-specific antagonists, adenosine 3'-phosphate 5'-phosphosulfate (A3P5PS), adenosine 3'-phosphate 5'-phosphate (A3P5P), and adenosine 2'-phosphate 5'-phosphate (A2P5P), in a concentration-dependent manner, but not by ARL 66096 or alpha, beta-MeATP. A3P5PS, A3P5P, and A2P5P also inhibited the shape change of aspirinated platelets induced by 10 microM ADP or 3 microM 2-methyl-(thio)-ADP in a concentration-dependent manner, with complete inhibition occurring at 300 microM. On the other hand ARL 66096 (100 nM), a potent P2TAC antagonist and alpha, beta-methylene-ATP (40 microM), a P2X1 receptor agonist, had no effect on ADP-induced platelet shape change. On the contrary, ADP-induced inhibition of adenylyl cyclase was blocked by ARL 66096, but not by alpha, beta-MeATP or the P2Y1 receptor-specific antagonists, A3P5PS, A3P5P, or A2P5P. These results demonstrate the role of the P2Y1 receptor in ADP-induced platelet shape change and calcium mobilization and support the idea that several P2 receptors are involved in the regulation of different aspects of platelet stimulus-response coupling.

[Multilocular cyst of kidney]

OBJECTIVE

Multilocular cyst of kidney is a rare, unique and characteristic renal lesion with benign biologic behavior. We report a case of the disease.

METHODS

It was confirmed by operation and pathology.

RESULTS

It is difficult to distinguish radiologically multilocular cyst of kidney from cystic renal carcinoma and wilms tumor.

CONCLUSION

Surgical intervention is the only effective treatment and method to differentiate multilocular cyst of kidney from a malignant lesion of the kidney.

Cardiokymograph system with a capacitance transducer and its preliminary application in the measurement of heart wall movement

A novel cardiokymograph system is introduced. The new system features a capacitance transducer with increased sensitivity and can be used in multichannel measurements. The novelty of this technique is the injection of a current into the patient coupled with the use of a capacitive displacement transducer and the possibility of multichannel monitoring. It provides for the possibility of removing breath noise when some signal processing technique, such as adaptive filtering, is used. Further investigation is needed to demonstrate clinical significance and pathologies.

Analysis of the Morgan-Elson chromogens by high-performance liquid chromatography

The Morgan-Elson method for quantitative N-acetylhexosamine analysis is a two-step procedure comprising alkali treatment of the sugar and subsequent condensation of the resulting chromogens with p-dimethylaminobenzaldehyde (Ehrlich's reagent) to yield a colored product. In the present investigation, the products formed in the first step of the procedure were analyzed by high-performance liquid chromatography (HPLC) on a reversed-phase (C18) column, which was eluted with a water-methanol gradient; the absorbance of the effluent was monitored at 229 nm. The profile generated from alkali-treated N-acetylglucosamine exhibited two major peaks, in a ratio of approximately 2.5:1, which accounted for 94% of the total peak area. A third peak, accounting for 3% of the peak area, was eluted in an intermediate position, and several smaller peaks were also observed. The three predominant components, isolated by preparative HPLC, all gave a purple color on addition of Ehrlich's reagent, indicating that they were Morgan-Elson chromogens. The HPLC profile of alkali-treated N-acetylmannosamine was identical to that of the products generated from N-actylglucosamine, as was expected because of the elimination of the asymmetry at C-2 during formation of the chromogens. N-Acetylgalactosamine yielded two major peaks, which were eluted in the same positions as the two major products formed from N-acetylglucosamine, but the intermediate peak seen in the N-acetylglucosamine pattern was absent. The HPLC procedure allowed detection of as little as approximately 25 ng of N-acetylglucosamine and may therefore be of value as an alternative to the complete Morgan-Elson procedure when only small amounts of sample are available for quantitative analysis.

Mechanical analysis and treatment of Harrington-rods broken after initial operation for scoliosis

Twenty-two cases of scoliosis with Harrington-rods broken after operation were treated by rod-sleeve method. The results of follow-up from 1 year and 3 months to 9 years and 3 months showed that all of the patients, but one patient occurred Harrington-rod rebroken and one's fixation being removed because of back pain in 6 months and 5 years and 11 months after rod-sleeve procedure, respectively, had no complaints. The author also found that the rod underwent a decrease in cross-sectional area of approximately 43.7% at the ratchet-shaft junction in experimental study on Harrington-rods, and stress unfairly distribution, stress concentration and cyclic loading producing fatigue in metals were proved to be the main cause of broken by mechanical analysis of Harrington-rod loaded in the body. In concluson, the rod-sleeve procedure was the effective method to keep from Harrington-rods broken.

Kainate induces the expression of the DNA damage-inducible gene, GADD45, in the rat brain

The expression of the novel growth arrest and DNA damage-inducible gene GADD45 was examined in kainate-induced epileptic brain damage in the rat using in situ hybridization, northern blot analysis, western blot analysis and immunocytochemistry. Systemic administration of kainate resulted in DNA damage and neuronal degeneration in vulnerable neurons of limbic regions, including the amygdala and hippocampal pyramidal layers, as shown by in situ DNA nick end-labelling and histological staining. GADD45 messenger RNA was transiently increased in non-vulnerable neurons (2-8 h after kainate injection) but was persistently elevated in vulnerable neurons (up to 24 h after injection) after kainate injection. GADD45 protein was elevated in both vulnerable and non-vulnerable neurons at 4 h, but levels decreased in vulnerable neurons thereafter, suggesting that translational blockage of GADD45 protein occurred in these cells. GADD45 protein was overexpressed in non-vulnerable neurons up to 72 h after kainate injection. Because GADD45 may participate in the DNA excision repair process and because it has been shown to be overexpressed in neurons that survive focal cerebral ischaemia, these results support the hypothesis that GADD45 may have a protective role in the injured brain.

On the SAR and field inhomogeneity of birdcage coils loaded with the human head

Birdcage coils are widely used as a radiofrequency (RF) resonator in magnetic resonance imaging (MRI) because of their capability to produce a highly homogeneous B1 field over a large volume within the coil. When they are employed for high-frequency MRI, the interaction between the electromagnetic field and the object to be imaged deteriorates the B1-field homogeneity and increases the specific absorption rate (SAR) in the object. To investigate this problem, a finite-element method (FEM) is developed to analyze the SAR and the B1 field in a two-dimensional (2D) model of a birdcage coil loaded with a 2D model of a human head. The electric field, magnetic field, and SAR distributions are shown, and a comprehensive study is carried out for both linear and quadrature birdcage coils at 64, 128, 171, and 256 MHz. It is shown that to generate the same value of the B1 field, the SAR is increased significantly with the frequency, and for the same imaging method the SAR produced by a quadrature coil is significantly lower than that of a linear coil. It is also shown that the B1-field inhomogeneity is increased significantly with the frequency.

[R wave relative oscillometric blood pressure measurement]

To improve the accuracy of oscillometric blood pressure measurement, an artifact rejection method for oscillations detection called R wave-relative method was developed. It was mainly based on the correlation between ECG R wave and oscillation. Combining with identification of oscillation characteristics this method can distinguish valid signals from interference. This algorithm has been implemented in 8098 microcontroller. Its program flowchart has also been presented in this paper.

[Primary and secondary structure of 3'--end of the large subunit ribosomal RNA of silkworm Attacus ricini and evolution implications as inferred from the gene sequence]

The DNA sequence of the 3'-end of LSu-rRNA coding region of silkworm Attacus ricini was determined. By comparisons with the corresponding sequence of H. sapiens, X. leavis, H. momus, A. albopictus, D. melanogaster, C. elegants, S. pombe, M. musculus and M. racemosus, we found that the coding sequence we obtained is very conserved. Phylogenetic tree inferred by Neighbor-joining Method showed that the rate of evolution of insects was much faster than vertebrate. In addition, the secondary structure has also worked out it is highly conserved.

[Investigation of analytical methods of laser photothermal spectroscopy for trace microchemical analysis]

The purpose of this work is to investigate the analytical characteristics of laser photothermal spectroscopy and discuss the feasibility to performance trace microchemical analysis by analytical methods of laser photothermal spectroscopy.

Characterization of S1 nuclease sensitive site at transcription initiation region of Attacus ricini rDNA

A single-stranded S1 nuclease hypersensitive site which contains a d(AT)(18) sequence structure located in the 5'-non transcription spacer of silkworm A. ricini ribosomal RNA gene has been reported([1]). Using starved-refed silkworms, another S1 nuclease sensitive site was found existing in the rDNA chromatin, while under merely starving, this S1 sensitive site disappeared([2]). Recently this inducible S1 sensitive site has been further determined. It consists of a d(GT)(10)-d(AT)(10) special DNA sequence at the transcription initiation region, and shows a behavior of ease in DNA-unwinding, indicating that S1 nuclease sensitive sites may have an important function in the regulation of rDNA transcription and replication.

[Study on polysaccharide of Lobaria kurokauae]

LOK polysaccharide is isolated from Lobaria kurokauae. By chromatography, LOK is shown to be sing substance. By gas chromatography analysis, LOK composes of rhamnose, arabinose, xylose, mannose, glucose and galactose. Their molecule ratio is about 1.00:1.34:1.12:10.13:6.99:6.47. Its mean molecule weight is estimated to be 1.5 x 10(4), its main chain is joined by a (1-->4) and a (1-->6) glucosidic linkages.

Colocalization of P2Y2 and P2Y6 receptor genes at human chromosome 11q13.3-14.1

Extracellular nucleotides mediate a number of physiological responses through either ligand gated P2X or G protein-coupled P2Y receptors. To date, six P2Y receptor subtypes, P2Y1-P2Y6, have been cloned. We mapped the human P2Y6 receptor gene to chromosome 11q13.3-13.5. Oligonucleotide primers complementary to a part of the human P2Y6 receptor cDNA were used to amplify a region from genomic DNA from a panel of mouse/human somatic cell hybrid cell lines, each containing a single human chromosome. A PCR product of the expected size (714 bp) resulted from a single hybrid cell line containing human chromosome 11. The gene was further localized to a region of chromosome 11 using a subchromosomal hybrid panel containing different segments of chromosome 11. Based on the specific PCR product obtained and its Southern hybridization to the P2Y6 receptor cDNA, the human P2Y6 receptor gene was localized to chromosome 11q13.3-13.5. Previously, we have localized the P2Y2 receptor gene to human chromosome 11q13.5-14.1. This is the first report of the clustering of the P2 receptor genes. The clustering of these two P2Y receptor subtypes suggests a relatively recent expansion of the gene family by gene duplication.

Inhibitory receptors, ITIM sequences and phosphatases

A diverse group of inhibitory receptors, including FcgammaRII, killer cell inhibitory receptors, and B22, shares an immunoreceptor tyrosine-based inhibition motif (ITIM). Recent studies have shown that this motif, when phosphorylated on tyrosine, forms a docking site for the Src homology 2 recognition domains of the protein tyrosine phosphatase SHP-1 and the inositol 5-phosphatase SHIP. A similar motif in cytotoxic T-lymphocyte antigen-4 recruits the related tyrosine phosphatase SHP-2. These three enzymes act to inhibit signaling cascades resulting from ligation of the BCR, TCR, FcgammaRIII, and FcepsilonRI, although the relative importance of the tyrosine phosphatases and the inositol phosphatase differs depending on the cell type.

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.