Chimera Patterns of Synchrony in a Frustrated Array of Hebb Synapses.

The union of the Kuramoto-Sakaguchi model and the Hebb dynamics reproduces the Lisman switch through a bistability in synchronized states. Here, we show that, within certain ranges of the frustration parameter, the chimera pattern can emerge, causing a different, time-evolving, distribution in the Hebbian synaptic strengths. We study the stability range of the chimera as a function of the frustration (phase-lag) parameter. Depending on the range of the frustration, two different types of chimeras can appear spontaneously, i.e., from randomized initial conditions. In the first type, the oscillators in the coherent region rotate, on average, slower than those in the incoherent region; while in the second type, the average rotational frequencies of the two regions are reversed, i.e., the coherent region runs, on average, faster than the incoherent region. We also show that non-stationary behavior at finite N can be controlled by adjusting the natural frequency of a single pacemaker oscillator. By slowly cycling the frequency of the pacemaker, we observe hysteresis in the system. Finally, we discuss how we can have a model for learning and memory.

Multivariate spectrofluorimetric detection of lipase isolated from Serratia marcescens in chromatographic fractions.

Lipases are ubiquitous enzymes and widespread in nature. They have been widely purified as one of the most important enzymes in molecular biosciences and biotechnology. In this paper, the extracellular lipase was separated from Serratia marcescens. The separated enzyme was purified partially by ammonium sulfate precipitation, dialysis and gel filtration chromatography. Presence of the lipase in chromatography fractions was assayed by the hydrolysis of paranitrophenyl palmitate (pNPP) as substrate. The excitation and emission (EEM) fluorescence spectra of purified lipase in chromatographic fractions were investigated. The study demonstrates an application of fluorescence spectroscopy, combined with multivariate regression methods, to the analysis of fluorescent lipase component. N-way partial least squares (N-PLS) was utilized to show the importance of region selection in calibration modeling of the data. Genetic algorithm (GA) optimization was applied to improve the performance of radial basis function network based regression model. RBF-ANN was used to calibrate and predict lipase activity. The analytical performance of RBF-ANN method was characterized by Q^2parameter. The value of Q^2 was 0.919. The proposed method was successfully applied to the analysis of protein containing fractions and in order to explore the three way fluorescence data array from separated fractions, parallel factor analysis (PARAFAC) was applied. The fluorescence signal was resolved into excitation and emission profiles of the pure fluorescent compounds.

In vitro single-unit recordings reveal increased peripheral nerve conduction velocity by focused pulsed ultrasound.

Ultrasound that is widely used in medical diagnosis has drawn growing interests as a noninvasive means of neuromodulation. Focused pulsed ultrasound (FPUS) effectively modulates neural encoding and transmission in the peripheral nervous system (PNS) with unclear mechanism of action, which is further confounded by contradictory experimental outcomes from recordings of compound action potentials (CAP). To address that, we developed a novel in vitro set up to achieve simultaneous single-unit recordings from individual mouse sciatic nerve axon and systematically studied the neuromodulation effects of FPUS on individual axon. Unlike previous CAP recordings, our single-unit recordings afford superior spatial and temporal resolution to reveal the subtle but consistent effects of ultrasonic neuromodulation. Our results indicate that, 1) FPUS did not evoke action potentials directly in mouse sciatic nerve at all the tested intensities (spatial peak temporal average intensity, ISPTA of 0.91 to 28.2 W/cm2); 2) FPUS increases the nerve conduction velocity (CV) in both fast-conducting A- and slow-conducting C- type axons with effects more pronounced at increased stimulus duration and intensity; and 3) effects of increased CV is reversible and cannot be attributed to the change of local temperature. Our results support existing theories of non-thermal mechanisms underlying ultrasonic neuromodulation with low-intensity FPUS, including NICE, flexoelectricity, and solition models. This work also provides a solid experimental basis to further advance our mechanistic understandings of ultrasonic neuromodulation in the PNS.

Is current smoking status and its relationship to anti-cyclic citrullinated peptide antibodies a predictor of worse response to biological therapies in rheumatoid arthritis patients?

OBJECTIVE: To assess the association between smoking, anti-cyclic citrullinated peptide (anti-CCP) antibody status, and clinical efficacy of biological therapies in rheumatoid arthritis (RA) patients. METHOD: This retrospective clinical practice setting study included 1349 RA patients from the METEOR database (aged >18 years). We collected data on sociodemographics, smoking status (smoker, <10, 10-19, and >20 cigarettes/day; ex-smoker; non-smoker), baseline disease activity parameters and anti-CCP, previous disease-modifying anti-rheumatic drugs (DMARDs), biological therapy, combined therapy (steroids and DMARDs), and follow-up disease activity. Clinical efficacy was assessed by European League Against Rheumatism (EULAR) good/moderate response rates for all aggregated biological therapies, based on both smoking and anti-CCP status. RESULTS: The non-smoking RA patients were more often female at biological therapy initiation than the ex-smokers and smokers (91.1% vs 60.4% and 67.9%, respectively, p < 0.001), and ex-smokers were older than non-smokers and smokers (mean ± sd 56.5 ± 11.1, 53.5 ± 13.3 and 51.3 ± 11.0 years old, respectively; p < 0.001). In total, 845 (62.6%) were non-smokers, 214 (15.9%) ex-smokers, and 290 (21.5%) smokers [daily cigarettes smoked: 148 (11%) <11; 61 (4.5%) 11-20; and 81 (6%) >20]. Anti CCP-antibody status was similar in both groups. Non-smokers showed higher baseline DAS28 than ex-smokers and smokers (5.0 ± 1.5 vs 4.7 ± 1.4 and 4.7 ± 1.4, respectively; p < 0.001) and used more baseline steroids and DMARDs. A higher EULAR response rate was observed in non-smokers than in ex-smokers and smokers (73% vs 65% and 64.1%, respectively; p = 0.004). Drug survival was higher in non-smokers compared to ex-smokers and smokers [57.7 months (46.4-53.8), 38.6 (30.3-46.8), and 50.1 (41.8-58.4); p < 0.001, respectively]. CONCLUSION: In daily clinical practice, non-smokers respond better than smokers to biological therapy, but this does not result in better drug survival.

Mycosis fungoides two decades after exposure to sulphur mustard: a follow-up of 1100 victims.

BACKGROUND: Sulphur mustard (SM) is an alkylating chemical warfare agent which causes acute and chronic injuries to the eyes, skin, lung and respiratory tract. OBJECTIVE: We aimed to investigate the relationship between SM poisoning and Mycosis fungoides (MF) as a late consequence. MATERIAL AND METHODS: In this retrospective study, the medical files of 1100 Iranian veterans confirmed to have exposure to SM agent during the Iraq-Iran war of the 1980s were reviewed. RESULTS: All 10 cases with MF were confirmed by clinical and histopathological examinations. The mean age of the studied subjects was 43.3 ± 9.8 (years). In comparison to MF incidence rate in Iranian general population (0.39/100 000 person-years), we found an incidence rate of 0.799/100 000 person-years for MF among those who had short-term exposure to SM. The most common sites for SM lesions were flexural and thin skin areas. The main limitation was the retrospective design. CONCLUSION: This study indicates that the risk of MF in those exposed to SM may increase over time. Therefore, their follow-up is recommended.

In vitro multichannel single-unit recordings of action potentials from mouse sciatic nerve.

Electrode arrays interfacing with peripheral nerves are essential for neuromodulation devices targeting peripheral organs to relieve symptoms. To modulate (i.e., single-unit recording and stimulating) individual peripheral nerve axons remains a technical challenge. Here, we report an in vitro setup to allow simultaneous single-unit recordings from multiple mouse sciatic nerve axons. The sciatic nerve (~30 mm) was harvested and transferred to a tissue chamber, the ~5mm distal end pulled into an adjacent recording chamber filled with paraffin oil. A custom-built multi-wire electrode array was used to interface with split fine nerve filaments. Single-unit action potentials were evoked by electrical stimulation and recorded from 186 axons, of which 49.5% were classed A-type with conduction velocities (CV) greater than 1 m/s and 50.5% were C-type (CV < 1 m/s). The single-unit recordings had no apparent bias towards A- or C-type axons, were robust and repeatable for over 60 minutes, and thus an ideal opportunity to assess different neuromodulation strategies targeting peripheral nerves. For instance, ultrasonic modulation of action potential transmission was assessed using the setup, indicating increased nerve conduction velocity following ultrasound stimulus. This setup can also be used to objectively assess the design of next-generation electrode arrays interfacing with peripheral nerves.

Radiographic depiction of intra-abdominal fat in newborns: a marker of infants born to diabetic mothers.

OBJECTIVE: To examine whether the presence of intra-abdominal fat (IAF) in newborns is diagnostic of infants of diabetic mothers (IDMs), and determine whether IAF is merely the consequence of increased body size. STUDY DESIGN: Abdominal radiographs of 277 neonates >34 weeks gestational age (147 male and 130 female) were reviewed to determine the presence of IAF. Unpaired t-test and regression analyses were used to examine the influence of gestational age, birth weight, birth length and maternal diabetes on the prevalence and thickness of IAF. RESULT: The prevalence of IAF was higher in IDMs (41.2% vs 13.2%; P<0.0001)-an association that persisted even after accounting for sex, gestational age and weight. Both birth weight and maternal diabetic status influenced the amount of IAF. Values of IAF thickness in IDMs were, however, more than threefold greater than those in non-IDMs (2.53±2.08 vs 0.81±0.29 mm; P<0.0001). An IAF thickness >1.5 mm was indicative of an IDM. CONCLUSION: The depiction of IAF in radiographs is significantly more prevalent in IDMs when compared with non-IDMs, regardless of body size. A thickness of IAF >1.5 mm is a marker that should encourage work-up for the physiological, metabolic and congenital complications associated with IDM.

Enhancing the care of women with rheumatic diseases during pregnancy: challenges and unmet needs in the Middle East.

Pregnancy in women with rheumatic disorders is known to be associated with risks for both the mother and fetus; however, these risks can be minimized with proper planning and careful management of the disease. In the Middle East, there are specific cultural challenges that may have a negative impact on the care that women with rheumatic disorders receive. There is a need for cross-collaboration between specialist physicians, improved awareness of rheumatic disorders among the general public and more open discussion with patients about the potential complications of pregnancy. Women in the region are often unwilling to discuss their disease with their partner and are even less likely to seek advice regarding family planning from their physician. The objective of this review is to highlight the specific challenges of pregnancy management and to discuss why establishing specialist pregnancy clinics for women with rheumatic disorders could be an effective solution. Such clinics can provide high quality care before, during and after pregnancy as shown in several European and US centers. Additionally, such clinics could be useful for the collection of pregnancy outcomes data from the Middle East, which may currently be lacking in the region, in order to highlight where further improvements can be made. With specialist care and analysis of pregnancy outcomes, the standard of care for women with rheumatic disorders in this area could be significantly improved.

Administration of estradiol benzoate before insemination could skew secondary sex ratio toward males in Holstein dairy cows.

The present study was conducted to investigate the effect of estradiol benzoate administration before insemination on secondary sex ratio (proportion of male calves at birth) in Holstein dairy cows. Cows (n = 1,647) were randomly assigned to 2 experimental groups by parity over a 1-yr period. Cows in the control group (n = 827; 232 primiparous and 595 multiparous cows) received 2 administrations of PGF2α (500 µg) 14 d apart, started at 30 to 35 d postpartum. Twelve d after the second PGF2α injection, cows received GnRH (100 µg), followed by administration of PGF2α 7 d later. Cows in the treatment group (n = 820; 238 primiparous and 582 multiparous cows) received the same hormonal administrations as the cows in the control group. Additionally, cows in the treatment group received estradiol benzoate (1 mg) 1 d after the third PGF2α injection. Estrus detection by visual observation was started 1 d after the third PGF2α injection and after estradiol administration in the control (for 6 d) and treatment (for 36 h) groups, respectively. Artificial insemination was carried out 12 h after observation of standing estrus. Exposure of cows to heat stress at conception was determined based on temperature-humidity index. Estrus detection rate was lower in primiparous than in multiparous cows (P < 0.05), but conception rate was higher in primiparous vs multiparous cows (P < 0.05). Estradiol administration improved estrus detection rate and fertility (P < 0.05); moreover, it increased secondary sex ratio (adjusted odds ratio: 1.645; P = 0.017). Exposure to heat stress diminished heat detection rate and fertility (P < 0.05), and altered secondary sex ratio toward males (adjusted odds ratio: 2.863; P = 0.012). In conclusion, the present study revealed that estradiol administration before insemination could improve fertility and increase the probability of calves being male in Holstein dairy cows. Moreover, the results showed that cows exposed to heat stress around conception had diminished fertility and increased secondary sex ratio.

MicroRNA-146a expression and its intervention in NF-кB signaling pathway in diabetic rat aorta.

OBJECTIVE: The present study was designed to evaluate whether microRNA-146a, as an NF-кB regulating factor and its adapter proteins (TRAF6 and IRAK1), are affected by diabetes in rat aorta. METHODS: Male Wistar rats were randomly divided into control and diabetic groups (n=6 in each). Diabetes was induced by a single injection of streptozotocin (55 mg/kg; i.p.) in 12 h fasted rats. The gene expression of microRNA-146a, NF-κB, IRAK1, and TRAF6 were determined by real time PCR. RESULTS: The expression of microRNA-146a was down-regulated in diabetic aorta when compared with the control group (p<0.05). The mRNA expression levels of NF-кB, TRAF6 and IRAK1 also increased in the diabetic rat aorta when compared with their control counterparts (p<0.01 for all comparisons). CONCLUSION: These results suggest that down-regulation of microRNA-146a may lead to derangement in NF-кB negative feedback loop, propelling the aorta toward inflammation.

Prevalence of HLA-B27 in Patients with Ankylosing Spondylitis in Qatar.

Background and Objectives. The human leukocyte antigen HLA-B27 is a class 1 antigen of the major histocompatibility complex and is strongly associated with ankylosing spondylitis (AS). The purpose of the present study is to investigate the distribution of HLA-B27 in patients with AS of different ethnic groups in Qatar. Design and Setting. Study design was cross-sectional and the setting was rheumatology clinics of Hamad General Hospital in Qatar where most of ankylosing spondylitis patients are followed up. Patients and Methods. Patients with diagnosis of AS who met the New York modified criteria for AS were tested for HLA-B27. 119 patients were tested for HLA-B27: 66 Arabs, 52 Asians (Indians, Pakistanis, Bengalis, and Iranians), and one Western (Irish). Results. Of all the individuals, 82 were positive (69%) for HLA-B27. Among the Arabs, 49/66 were positive (74%). Among the Asians, 32/52 were positive (61%). Furthermore, Qatari patients (10 males and one female) 9 were positive (82%), 14/19 Jordanians/Palestinians were positive, and 9/10 (90%) Egyptians were positive. Among the Asians, 19/26 Indians were positive (73%), which was similar to the Arabs. Conclusion. HLA-B27 in our small group of Arabs is present in 74%. Comparison with other data will be presented in detail.

Urinary and cutaneous complications of sulphur mustard poisoning preceding pulmonary and ocular involvement: an unusual sequence of symptoms.

Sulphur mustard was used as a disabling chemical warfare agent during World War I, and, in more recent times, the Iran-Iraq conflict. Various chronic and acute complications have been documented in almost 100,000 Iranian victims to date. Several individual and environmental factors affect the severity and persistency of the complications. The most common adverse effects occur in the respiratory system, skin and eyes, with ocular and respiratory features usually preceding cutaneous lesions. In this paper, we present the unusual case of a chemical victim presenting with characteristic mustard scar leading to stenosis of the external meatus. In this case, initial cutaneous involvement of the injured external genitalia and thighs preceded the ocular and respiratory symptoms. We discuss the possible aetiologies.

Cellular source of human platelet secretory phospholipase A2.

Platelets are one source of the group II extracellular form of phospholipase A2 (sPLA2) which is involved in the amplification of local and systemic inflammation. Although sPLA2 protein has been described in human platelets, its presence in human megakaryocytes has not been yet established. We demonstrated in this study that the human erythroleukaemia (HEL) cell line, which has megakaryoblastic features, constitutively expresses sPLA2. Using an anti-rhsPLA2 monoclonal antibody (mAb BA11) and dot-blot detection, we showed that HEL cells and platelets release sPLA2 into incubation medium upon stimulation by thrombin. Similar results were obtained for sPLA2 activity detected by a spectrofluorescence assay. Enzymatic activity was abolished by mAb BA11 and by protamine. In both cell types, although released, the major part of sPLA2 remained in the cell pellet, and was probably adsorbed at non-specific membrane sites. Double labelling experiments using mAb BA11 and an anti-GPIIb antiserum revealed the presence of sPLA2 in human bone-marrow megakaryocytes. The use of reverse transcription-polymerase chain reaction conjugated with hybridization analysis demonstrated the presence of mRNA encoding for sPLA2 in platelets and HEL cells. Expression of sPLA2 in platelets and megakaryocytes at both transcriptional and post-translational levels strongly argues in favour of a megakaryocytic origin of platelet sPLA2 and rules out a role for endocytosis of the enzyme from plasma by circulating platelets.

Signal transduction involved in the platelet adenylate cyclase sensitization associated with PGH2/TxA2 receptor desensitization.

The exposure of human platelets to prostaglandin H2 analogue (PGH2, U46619) induces homologous desensitization and a concomitant adenylate cyclase (AC) sensitization. We demonstrate the involvement of phospholipase C (PLC) in this enzyme sensitization. Pre-incubation of platelets with neomycin, a PLC activity inhibitor, prevented AC sensitization but not PGH2/thromboxane (Tx)A2 receptor desensitization. PGH2/TxA2 receptor desensitization, although necessary, is not sufficient to induce AC sensitization, since neomycin, which prevents AC sensitization, failed to prevent receptor desensitization. Inositol phosphate formation, determined in parallel, was also inhibited. Interestingly, no guanylate cyclase sensitization was noted, suggesting a specific relationship between PGH2/TxA2 receptor desensitization and AC sensitization. In addition, using alkaline phosphatase, a dephosphorylating enzyme, and the tyrosine kinase inhibitor erbstatin, we examined the role of phosphorylation-dephosphorylation on AC sensitization. Effectively, alkaline phosphatase, which has no effect by itself, enhances the cAMP production triggered by prostacyclin in control but not in desensitized platelets. In contrast, erbstatin failed to modify this synthesis, indicating the non-involvement of tyrosine kinase pathway in this process. Our results indicate that the AC sensitization was mediated by PLC and also suggest the participation of other mechanisms, including phosphorylation-dephosphorylation processes. This specific enzyme sensitization may be relevant for the in vivo modulation of platelet activation, in different thrombotic diseases with an increased TxA2 generation.

Comparative effects of recombinant staphylokinase and streptokinase on platelet aggregation.

Recombinant staphylokinase (RSTA) has been shown to offer promise as a thrombolytic agent. In contrast to streptokinase (SK), few studies have been devoted to possible effects of RSTA on platelets. We have compared the capacity of RSTA and SK to trigger platelet aggregation and to modify ADP (2.5 microM) response in platelet-rich plasma (PRP) of 125 healthy subjects. Thus, exposure of PRP to SK (40 to 50 micrograms/ml) induced platelet aggregation in 6 out of 25 subjects. However, under the same conditions, RSTA failed to induce platelet aggregation in all cases (25 out of 25 subjects). In contrast to RSTA, SK (0.4 to 50 micrograms/ml) greatly reduced ADP-induced platelet aggregation in 12 out of 25 subjects. Preincubation of plasma with SK is associated with a decrease in the fibrinogen concentration. Furthermore, there was a good correlation between SK-induced fibrinogenolysis and SK-induced platelet aggregation defect (r2 = 0.9; p = 0.001). No fibrinogenolysis was observed when different amounts of RSTA (0.4 to 50 micrograms/ml) were incubated in plasma for one min. However, there was a marked decrease in fibrinogen level (about 50%) when the plasma was incubated for five min with a very high concentration of RSTA. SK markedly enhanced the platelet response to ADP in 13 out of 25 subjects. In PRP of 6 out of 25 subjects, SK induces platelet aggregation and potentiates platelet response to ADP, however in PRP of 7 out of 25 subjects, SK caused only the increase of platelet response to ADP. The monoclonal antibody anti-Fc gamma RIIa1, I-3 (2 micrograms/ml), abolished SK-induced platelet aggregation and SK-enhanced ADP-induced platelet aggregation. In all cases (25 out of 25 subjects), RSTA failed to potentiate platelet response to ADP. These findings confirm that RSTA has a lesser fibrinogenolytic ability than SK and suggest its negligible effect on platelet function.

Signal transduction in the platelet activation induced by IgG anti-streptokinase and anisoylated plasminogen-streptokinase activator complex.

Streptokinase (SK) is one of the plasminogen activators currently used in therapeutics. SK antibodies may appear in the blood after thrombolytic therapy with SK or after ss-hemolytic streptococci infection. Such antibodies may both activate platelets and neutralize the ability of SK to convert plasminogen into plasmin. We previously demonstrated that platelet activation induced by the combination of IgG anti-SK and anisoylated plasminogen-SK activator complex (APSAC) is mediated by Fgamma7RIIal receptor. However, the mechanism by which IgG anti-SK and APSAC (or SK) transduce an activating signal across the platelet plasma membrane remains unknown. We have demonstrated in the present study that the platelet aggregation induced by the combination of IgG anti-SK and APSAC is accompanied by an increase in inositol phosphate, Ca(2+) mobilization and thromboxane (Tx) A2 generation. Neomycin, erbstatin and GF 109203X, which inhibit phospholipase C (PLC), protein tyrosine kinase (PTK) and protein kinase C (PKC) activities, respectively, abolished platelet aggregation induced by IgG anti-SK plus APSAC, indicating the pivotal roles of the PLC, PTK and PKC pathways in this immunological activation. In addition, TxA2 generation is also important since aspirin, a cyclo-oxygenase inhibitor and SQ 29548, a TxA2 receptor antagonist, showed significant inhibition of the platelet response. The contribution of released ADP was confirmed using apyrase, which significantly inhibited IgG anti-SK plus APSAC-induced platelet aggregation. Finally, WEB 2086, a platelet-activating factor (PAF) receptor antagonist, was not effective, indicating that PAF is not involved in this process. APSAC- or SK-induced platelet activation may limit the therapeutic effectiveness of the drug and may contribute to the pathogenesis of early reocclusion. The study of the mechanism leading to APSAC-induced platelet activation could be relevant for a better understanding of the physiopathology of immune complex disorder diseases and thrombolytic treatment failure.

Reversible inhibition by protamine of human synovial and rabbit platelet secretory phospholipase A2.

We investigated the effects of protamine on the release and the activity of 14 kDa type II phospholipase A2 (sPLA2). Protamine blocks both release and activity of sPLA2 from thrombin-stimulated platelets in a concentration-dependent manner. Heparin, an anionic sulfate polysaccharide which has a high affinity for this enzyme, has no inhibitory effect on sPLA2 by itself but it is able to reverse the inhibitory effect of protamine. The liberation by thrombin of platelet factor 4, an alpha-granule constituent, unlike to that of ATP stored in dense bodies, was suppressed by protamine. Platelet aggregation, determined in parallel, was not affected by protamine. Also, protamine did not inhibit platelet arachidonic acid liberation, which is mainly produced by cytosolic PLA2. The non-proteinaceous polycationic hexadimethrine and acidic protein casein failed to inhibit platelet sPLA2 activity. By contrast, the basic polypeptides poly(L-arginine) and poly(L-lysine) potently inhibited sPLA2 activity, indicating the important role of basic amino acids in the inhibitory effect evoked by protamine. Activities of the human recombinant sPLA2 and the unpurified synovial enzyme of patients with rheumatoid arthritis were also inhibited by the same range of protamine, poly(L-arginine) and poly(L-lysine) concentrations. Our results demonstrate that protamine, unlike heparin, blocks platelet sPLA2 release and exerts a reversible inhibitory effect on its activity, probably through the interaction of basic amino acids with the enzyme.

Dissociation between the phospholipases C and A2 activities in stimulated platelets and their involvement in the arachidonic acid liberation.

In previous work we have demonstrated that platelets depleted from secretory phospholipase A2 (sPLA2) produced similar amounts of thromboxane (Tx)B2 as control platelets upon stimulation by thrombin. However, since depletion of sPLA2 was not total, this sole finding only suggested the non-involvement of sPLA2 in arachidonic acid release. In the present study we provide further evidence for the non-involvement of sPLA2 in arachidonic acid liberation during platelet activation. Thus, rabbit platelets exposed to thrombin secreted sPLA2, released free arachidonic acid and formed TxB2 and inositol phosphates. In contrast, U46619, a stable prostaglandin (PG)H2 analogue, activates phospholipase C (PLC) and induces release of sPLA2 without TXB2 generation nor arachidonic acid liberation. At each concentration tested of both agonists, stimulation of sPLA2 activity paralleled the production of inositol phosphates. These data suggest that sPLA2 is dependent on phosphoinositide hydrolysis and on the release reaction and that it is not involved in the liberation of arachidonic acid from stimulated platelets. In addition, a dissociation was observed between sPLA2 and the enzyme involved in the arachidonic acid mobilization, suggesting that the liberation of this fatty acid from membrane phospholipids was mediated by cytosolic phospholipase A2 (cPLA2). Finally, PLC does not play a major role in arachidonic acid liberation, since U46619, which induced the breakdown of inositol phospholipids, failed to release arachidonic acid. In confirmation, neomycin, which inhibits PLC activity, failed to inhibit ATP, sPLA2 and arachidonic acid release upon stimulation of platelets by fluoroaluminate. These data demonstrate that sPLA2 is not involved in the arachidonic acid release by stimulated platelets and indicate that the activations of PLC, sPLA2 and cPLA2 are independent events.