bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black
Authors: Zhang Jie , Feng Shengyu , Ma Qingyu
Published: May 2003

The kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 5°C/min. The rate parameters were evaluated by the method of Freeman–Carroll. The results show that the thermal degradation of conductive silicone rubber begins at about 350°C and ends at about 600°C. The thermal degradation is multistage, in which zero‐order reactions are principal. The kinetics of the thermal degradation of conductive silicone rubber has relevance to its loading of conductive carbon black. The activation energies are temperature‐sensitive and their sensitivity to temperature becomes weak as temperature increases. In addition, the conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber without any fillers. Also, conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber filled with the same amount of silica. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1548–1554, 2003
Effect of glass transition on the concentration dependence of self‐diffusion coefficients
Authors: Vrentas J. S. , Vrentas C. M.
Published: May 2003

The free‐volume theory of diffusion is used to predict the effect of the glass transition on the concentration dependence of the solvent self‐diffusion coefficient at constant temperature. The theoretical prediction is in agreement with experimental data. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1682–1684, 2003
Blends of poly(propylene) and polyacetal compatibilized by ethylene vinyl alcohol copolymers
Authors: Huang Jieh‐Ming , Cheng Hua‐Jen , Wu Jiann‐Shing , Chang Feng‐Chih
Published: May 2003

Polymer blends of poly(propylene) (PP) and polyacetal (polyoxymethylene, POM) with ethylene vinyl alcohol (EVOH) copolymers were investigated by differential scanning calorimetry (DSC), rheological, tensile, and impact measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The PP–POM–EVOH blends were extruded with a co‐rotating twin‐screw extruder. The ethylene group in the EVOH is partially miscible with PP, whereas the hydroxyl group in the EVOH can form hydrogen bonding with POM. The EVOH tends to reside along the interface, acting as a surfactant to reduce the interfacial tension and to increase the interfacial adhesion between the blends. Results from SEM and mechanical tests indicate that a small quantity of the EVOH copolymer or a smaller vinyl alcohol content in the EVOH copolymer results in a better compatibilized blend in terms of finer phase domains and better mechanical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1471–1477, 2003
Computer simulation of conic‐shaped patterns on fracture surfaces of polymers
Authors: Wenbo Luo , Tingqing Yang
Published: May 2003

Fractographic analysis, using scanning electron microscopy, is an important method to study polymer fracture behavior. There are several distinctive patterns on fracture surfaces, such as radial striations, regularly spaced ‘rib’ markings, and conic‐shaped patterns. The conic‐shaped pattern is the intersection locus of a moving planar crack front and a radially growing circular craze or secondary crack front. In this paper, the effects of the ratio of crack velocity to growing craze or secondary crack velocity on the shape of intersection loci are discussed using computer simulations. It is shown that when the ratio of crack velocity to craze or secondary crack velocity ($\dot{a}/\dot{c}$) increases progressively, the fracture surface pattern changes from a parabola or a prolate parabola to an ellipse and finally to an approximate circle. Therefore, the crack growth velocity can be estimated based on the fracture surface morphology and then related to the fracture processes as well as to the ductile–brittle transition or toughening mechanism of brittle polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1722–1725, 2003
Electrochemical synthesis of poly(2‐iodoaniline) and poly(aniline‐co‐2‐iodoaniline) in acetonitrile
Authors: Şahin Yücel , Perçin Sabriye , Alsancak Güleren Özkan
Published: May 2003

Poly(2‐iodoaniline) (PIANI) and poly(aniline‐co‐2‐iodoaniline) [P(An‐co‐2‐IAn)] were synthesized by electrochemical methods in acetonitrile solution containing tetrabutylammonium perchlorate (TBAP) and perchloric acid (HClO4). The voltametry of the copolymer shows characteristics similar to those of conventional polyaniline (PANI), and it exhibits higher dry electrical conductivity than PIANI and lower than PANI. The observed decrease in the conductivity of the copolymer relative to PANI is attributed to the incorporation of the iodine moieties into the PANI chain. The structure and properties of these conducting films were characterized by FTIR and UV‐Vis spectroscopy and by an electrochemical method (cyclic voltametry). Conductivity values, FTIR and UV‐Vis spectra of the PIANI and copolymer were compared with those of PANI and the relative solubility of the PIANI and the copolymer powders was determined in various organic solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1652–1658, 2003
Synthesis, structure, and olefin polymerization catalysis of a novel vanadium(III) 1,1′‐bi‐2‐naphtholate complex
Authors: Sato Yoshinori , Nakayama Yuushou , Yasuda Hajime
Published: May 2003

The reaction of VCl3 with (S)‐(–)‐Na2 (binol) (binol = 1,1′‐bi‐2‐naphtholate) gave a new vanadium(III) complex, [Na(OEt2)]3[V(binol)3] (Fig. 1). The X‐ray crystallographic structure of this complex (Complex 1) in Figure 1 reveals its propeller‐like structure, which is similar to those of the reported rare earth analogues. The complex showed moderate catalytic activities for ethylene polymerization upon activation with modified methylaluminoxane (MMAO) and with diethylaluminum chloride (DEAC). The Complex 1/DEAC system also catalyzed the polymerization of propylene to give atactic polypropylene with low activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1659–1662, 2003

Complex 1

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1. Molecular structure of [Na(OEt2)]3[V(binol)3] (Complex 1).

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1. Molecular structure of [Na(OEt2)]3[V(binol)3] (Complex 1).
Studies on the silicone resins cured with polymethylsilazanes at ambient temperature
Authors: Zhang Yuemei , Huang Ying , Liu Xiangluan , Yu Yunzhao
Published: May 2003

Polymethylsilazanes (PMS) were synthesized and used to cure silicone resins at ambient temperature. The curing degree of the silicone resins depends on the structure of PMS and its concentration in the resin. Silicone resins of different structure and different silanol content can be cured to a satisfactory degree, if the concentration of the PMS is high enough. Silicone resins cured with PMS showed improved thermal stability in nitrogen, compared with that of the heat‐cured counterparts. The mechanism of thermal decomposition of the silicone resins is discussed. The improvement of heat resistance using PMS as the curing agent is accounted for by diminished thermal rearrangement and degradation of the polysiloxane network initiated by silanol groups in the resins. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1702–1707, 2003
Effect of molecular weight and branch content on the creep behavior of oriented polyethylene
Authors: O'Connell P. A. , Bonner M. J. , Duckett R. A. , Ward I. M.
Published: May 2003

Creep studies were carried out on a range of homopolymers and copolymers of polyethylene with well‐defined molecular weight and branch content. The creep data were analyzed in terms of two thermally activated processes acting in parallel and the effects of molecular weight and branch content are discussed. It is shown that increasing either the number‐average molecular weight or the weight‐average molecular weight gives improved creep behavior at all stress levels. The introduction of butyl branches leads to lower creep at low‐stress levels but can give rise to higher creep at high stress. Plots of the equilibrium log10(strain rate) versus stress at fixed draw ratio (strain) can be used to define sections through a unique true stress/true strain/strain rate surface for each material. These creep results have an additional value in terms of the link between slow crack propagation (SCG) in polyethylene and fibril creep, confirming the proposal made elsewhere that SCG can be quantified in terms of creep to failure across the true stress/true strain/strain rate surface. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1663–1670, 2003
Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. III. The relationship between the drying condition of the membrane and its permeation behavior
Authors: Abe Yoshihiko , Mochizuki Akira
Published: May 2003

The effects of drying condition on the performance (ultrafiltration rate, diffusive solute permeability, and sieving) of hemodialysis membranes prepared from cellulose/N‐methylmorpholine‐N‐oxide (NMMO) solution (NMMO membrane) and cellulose/cuprammonium solution (cuprammonium membrane; the referential membrane) were studied. The drying condition investigated was the glycerin concentration of the solution, which was used to substitute glycerin for the water in the membrane before the membrane was dried. A lower glycerin concentration in the solution brought about a lower reswelling degree (water content) in the dried membrane in pure water, which resulted in a drop in the performance of the as‐cast membrane. The NMMO membrane had a high water content and a high membrane performance compared with the cuprammonium membrane when both the membranes were treated under the same drying condition. The differences in the performance between both membrane series is discussed on the basis of the results of the observation of the membrane morphology by scanning electron microscopy, the observation of the crystallinity of the membranes by wide‐angle X‐ray diffraction, and the estimation of the pore structure of the membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1671–1681, 2003
Searching for complex CA rules with GAs
Authors: Bilotta Eleonora , Lafusa Antonio , Pantano Pietro
Published: May 2003

An important problem in the theory of cellular automata (CA) is the research of complex rules, the parameterization of the rule space, and the description of the CA dynamic behavior. In this article, the authors used evolutionary techniques in the search of CA with specific characteristics, in order to understand how their data are related to the previous findings in this sector. Using as fitness function, the variance of the input‐entropy, a genetic algorithm was built to search complex rules for multistate CA. The algorithm used is efficient and many complex rules have been found. Many of these rules present interesting characteristics. Gliders with large period and large spatial dimensions may be observed. The experiments performed show that complex rules have several λ values, which do not reside in a sharply defined region; on the contrary, these values are extended on very large regions of the λ parameter. The results provide also a view of the CA rule space. © 2003 Wiley Periodicals, Inc.
Quantifying the complexity of flow networks: How many roles are there?
Authors: Zorach Alexander C. , Ulanowicz Robert E.
Published: May 2003

Weighted flow networks are structures that arise naturally when analyzing complex systems. The countable properties of unweighted networks are not easily generalized to weighted networks. One candidate measure of complexity is the number of roles, or specialized functions in a network. It is easy to identify the number of roles in a linear or cyclic unweighted network. There is only one logically consistent way to generalize the measures of nodes, flows, connectivity, and roles into weighted networks, and these generalizations are equivalent to indices derived from information theory and used by ecologists since the late seventies. Data from ecosystem networks suggests that ecosystems inhabit a narrow window of the parameter space defined by these measures. © 2003 Wiley Periodicals, Inc.
Agent‐based model for economic impact of free software
Authors: Khalak Asif
Published: May 2003

This article describes the potential impact that free (i.e., open source) software can have on an existing commercial software market. A model for the software market is constructed in terms of autonomous agents, which represent the users, the companies, and the free software providers. The model specifies a reservation price for each user agent and develops a gradient learning strategy for revenue‐maximizing company agents. Simulations explore parameters such as the demand distribution, and the relative importance of market share, advertising and random effects in product visibility. Results from the case without free software show a prevalence of monopolies, which is consistent with other studies of high‐technology market economics. The effects of free software are not uniform, but are highly parameter dependent. A “capture region” is found in which free software eventually dominates the market. © 2003 Wiley Periodicals, Inc.
Recent developments in the field of A3 adenosine receptor antagonists
Authors: Baraldi Pier Giovanni , Tabrizi Mojgan Aghazadeh , Fruttarolo Francesca , Bovero Andrea , Avitabile Barbara , Preti Delia , Romagnoli Romeo , Merighi Stefania , Gessi Stefania , Varani Katia , Borea Pier Andrea
Published: May 2003

Adenosine is an endogenous modulator of a large variety of physiological functions through the interaction with specific cell membrane G‐protein‐coupled receptors classified as A1, A2A, A2B, and A3. Activation of A3 receptors has been shown to stimulate phospholipase C and to inhibit adenylate cyclase. A3 agonists also cause stimulation of phospholipase D and the release of inflammatory mediators, such as histamine from mast cells, which are responsible for inflammation and hypotension. For these reasons, the clinical use of A3 adenosine receptors antagonists for the treatment of asthma and inflammatory disease has been suggested. Recent studies also indicated a possible employment of these derivatives as antitumor agents. Different classes of polyheterocyclic compounds have been identified as potent A3 antagonists. Herein, we report our past and recent results in the development of tricyclic A3 selective antagonists. The pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine nucleus has especially been investigated by our group. Our interests were focused on the effects of substitution of the phenyl ring of the arylcarbamoyl moiety at N5 position and of substituents at C9 and/or at N8 pyrazole nitrogen. These studies allowed us to obtain a large variety of compounds which showed affinities in the nanomolar range with human A3 adenosine receptors with a high degree of selectivity vs. all other receptors subtypes. Thanks to the introduction of alkylating groups at p‐position of the N5‐phenylcarbamoyl chain, we succeeded in realizing potent irreversible A3 adenosine antagonists. Finally, the replacement of the phenyl nucleus of carbamoyl function with a pyridine ring conferred water solubility to the corresponding derivatives, which are also characterized by high levels of A3 affinity and selectivity. Drug Dev. Res. 58:315–329, 2003. © 2003 Wiley‐Liss, Inc.
Engineering of A3 adenosine and P2Y nucleotide receptors and their ligands
Authors: Jacobson Kenneth A. , Kim Hak Sung , Ravi Gnana , Kim Soo‐Kyung , Lee Kyeong , Chen Aishe , Chen Wangzhong , Kim Seong Gon , Barak Dov , Liang Bruce T. , Gao Zhan‐Guo
Published: May 2003

Modification of the ribose moiety of nucleotides and nucleosides has provided new insights into structural and conformational requirements for ligands at P2Y nucleotide receptors and at adenosine receptors (ARs). Methanocarba derivatives (containing a rigid bicyclic ring system in place of ribose) of adenosine, ATP, ADP, UTP, UDP, and other receptor agonist analogs were synthesized. Biological evaluation led to the conclusion that in general the Northern (N)‐conformation was favored over the Southern (S)‐conformation of the pseudoribose moiety at A1 and A3 ARs and at P2Y1, P2Y2, P2Y4, or P2Y11 receptors, but not P2Y6 receptors. At the hA3 AR a new full agonist, MRS1898, the (N)‐methanocarba equivalent of Cl‐IB‐MECA (2‐chloro‐N6‐(3‐iodobenzyl)‐5'‐N‐methylcarbamoyladenosine), had a Ki value of 1.9 nM in binding to the hA3 AR expressed in CHO cells. Functional assays confirmed the selectivity of MRS1898, although Cl‐IB‐MECA was even more functionally selective for human A3 vs. hA1 and hA2A ARs. Thirty µM MRS1898 did not induce apoptosis in HL‐60 cells, suggesting that some of the proapoptotic effects of Cl‐IB‐MECA may be nonreceptor‐mediated. Manipulation of the sequence of A3 ARs through site‐directed mutagenesis has led to pharmacologically unique constructs: constitutively active receptors and “neoceptors.” Such engineered receptors may later prove to have potential for cardioprotection through gene transfer. Effects of single amino acid replacement were interpreted using a rhodopsin‐based model of ligand‐A3 receptor interactions, leading to the proposal that a movement of the conserved W243 in TM6 may be involved in AR activation. Drug Dev. Res. 58:330–339, 2003. © 2003 Wiley‐Liss, Inc.
Hetero‐oligomerization between adenosine A1 and P2Y1 receptors in living cells: Formation of ATP‐sensitive adenosine receptors
Authors: Nakata Hiroyasu , Yoshioka Kazuaki , Saitoh Osamu
Published: May 2003

We explored the possibility of hetero‐oligomerization between Gi/o protein‐coupled A1 adenosine receptor (A1R) and Gq protein‐coupled P2Y1 receptor (P2Y1R) in transfected cultured cells by a new bioluminescence resonance energy transfer technology (BRET2) in addition to indirect biochemical or pharmacological methods. The existence of A1R/P2Y1R hetero‐oligomers in cotransfected HEK293T cells was first shown using coimmunoprecipitation methods. In the same cotransfected cells, ADPβS was able to reduce forskolin‐evoked cAMP accumulation in a pertussis toxin‐ and A1R antagonist‐sensitive manner, indicating that the pharmacology of A1R was significantly modified in the cotransfected cells, i.e., ADPβS binds A1R and inhibits adenylyl cyclase activity via Gi/o proteins. Also, a high degree of A1R and P2Y1R colocalization was demonstrated in cotransfected cells by double immunofluorescence experiments with confocal laser microscopy. Then the BRET2 technique revealed constitutive heteromeric oligomerization between A1R and P2Y1R in living HEK293T cells. The BRET2 signal also increased in a time‐dependent manner upon addition of agonists for both receptors, which was inhibited by pretreatment with the P2Y1R antagonist MRS2179, indicating that this process is promoted by the simultaneous activation of both receptors. These results suggest that the oligomeric association of A1R with P2Y1R generates A1R with P2Y1R‐like agonistic pharmacology and provides a molecular mechanism for an increased diversity of purinergic signaling. Existence of this hybrid purinergic receptor may explain the controversial inhibition of synaptic transmission by adenine nucleotides. Drug Dev. Res. 58:340–349, 2003. © 2003 Wiley‐Liss, Inc.
In vivo studies of the release of adenine 5′‐nucleotides, adenosine, and its metabolites from the rat brain
Authors: Phillis John W. , O'Regan Michael H.
Published: May 2003

Adenosine 5′ ‐triphosphate (ATP) and adenosine function as an excitatory neurotransmitter and a neuromodulator, respectively, in the central nervous system. Neuroexcitatory effects of ATP are mediated by P2X receptors: neuromodulator effects of adenosine by A1, A2, or A3 receptors. There is also evidence that ATP, acting a P2Y receptor, is involved in osmoregulatory responses to cell swelling. Studies on the release of ATP and/or adenosine into the interstitial fluid of the brain have served to clarify their roles in cerebral function. ATP release occurs during electrical or K+‐induced depolarization of cerebral tissues. Released ATP is rapidly hydrolyzed by ectonucleotidases, which may be released concurrently, to form adenosine 5′‐diphosphate (ADP) and adenine 5′‐monophosphate (AMP). In addition to synaptic release from neurons, there is evidence of glial release via gap‐junction hemichannels. Hydrolysis of AMP to adenosine initiates a further metabolic cascade with the formation of inosine, hypoxanthine, xanthine, and uric acid by adenosine deaminase, purine nucleoside phosphorylase, and xanthine oxidase. Hypoxanthine can be converted to inosine monophosphate by hypoxanthine phosphoribosyl transferase and thus used to replenish ATP. Cerebral ischemia causes ATP utilization, and adenosine formation. Adenosine can then be transported across the plasma membrane and released into the interstitial space. Hypoxemia‐evoked adenosine release from the cerebral cortex is inhibited by blockers of adenosine transport. Inhibition of purine metabolism by blockers of adenosine deaminase, purine nucleoside phosphorylase, and xanthine oxidase elevates upstream levels of adenosine and its metabolites. Exposure of the in vivo rat cerebral cortex to cerebrospinal fluid containing swelling‐inducing monocarboxylic acids elevated interstitial fluid levels of ADP and AMP, but not of adenosine. Taken together, these studies have led to a greater understanding of the metabolism and release of adenosine and the adenine nucleotides in the normoxic and ischemic brain. Drug Dev. Res. 58:412–419, 2003. © 2003 Wiley‐Liss, Inc.
Renal effects of BG9928, an A1 adenosine receptor antagonist, in rats and nonhuman primates
Authors: Ticho Barry , Whalley Eric , Gill Alan , Lutterodt Frank , Jin Xiaowei , Auchampach John , Smits Glenn
Published: May 2003

Stimulation of A1adenosine receptors in the kidney reduces glomerular filtration rate (GFR) via tubuloglomerular feedback and increases sodium reabsorption. Blocking A1 adenosine receptors would therefore maintain GFR and cause natriuresis. These attributes would be especially beneficial in treating congestive heart failure (CHF). BG9928 is a xanthine derivative that binds with high affinity to A1 adenosine receptors from several species including human and acts as a competitive antagonist at these receptors. This compound is being developed for the treatment of CHF. BG9928 receptor binding across a wide array of human and animal receptors was evaluated in vitro. Oral dose–response was assessed in rats, and oral and iv dose–responses were assessed in monkeys. The functional potency of BG9928 was demonstrated in vivo in rats. The binding affinity (Ki) for the human A1 adenosine receptor is 12.2 nM. BG9928 is orally active, with a dose of 0.3 mg/kg po achieving full natriuretic response in rats and with iv doses as low as 0.03 mg/kg showing activity in nonhuman primates. The renal protective effects of BG9928 were demonstrated by coadministration with the loop diuretic furosemide. In rats, administration of BG9928 effectively attenuated the reductions in GFR that usually occur with the administration of furosemide. Blockade of A1 receptors by BG9928 protects renal function against the adverse effects of loop diuretics and exerts additive natriuretic effects. In CHF patients, this profile may translate into significant clinical benefit by enhancing natriuresis with diminished concern of inducing renal insufficiency. Drug Dev. Res. 58:486–492, 2003. © 2003 Wiley‐Liss, Inc.
Impact of endogenous adenosine on airway hyperreactivity
Authors: Blackburn Michael R. , Young Hays W.J.
Published: May 2003

Adenosine signaling has been implicated in the exacerbation of chronic inflammatory lung diseases such as asthma. Challenging the airways with adenosine leads to bronchoconstriction; however, little is known about the role of endogenous adenosine on airway physiology. We examined the consequences of chronic adenosine elevations in mice genetically manipulated to contain low levels of the purine catabolic enzyme adenosine deaminase (ADA), which controls adenosine concentrations in tissues and cells. Examination of airway physiology in these animals revealed an increase in airway responsiveness. This increase in airway responsiveness was dependent on elevated adenosine in that treatment with ADA enzyme therapy reversed increased airway responsiveness in conjunction with lowering lung adenosine levels. Treatment with the broad‐spectrum adenosine receptor antagonist theophylline prevented airway hyperresponsiveness, implicating the involvement of adenosine receptors. Furthermore, transcript levels for the A1, A2B, and A3 adenosine receptors were elevated in the lungs of ADA‐deficient mice. These findings suggest that endogenous increases in lung adenosine concentrations are associated with alterations in airway physiology. Drug Dev. Res. 58:472–478, 2003. © 2003 Wiley‐Liss, Inc.
Evidence of tanscriptional and tanslational components in anti‐ischemic effects of adenosine
Authors: Headrick John P. , Peart Jason , Holmgren Kirsten , Ashton Kevin
Published: May 2003

Adenosine protects against myocardial ischemic injury via poorly defined mechanisms. We examined effects of inhibition of gene transcription, mRNA translation, and mitochondrial KATP channels on cardioprotective effects of adenosine in mouse hearts subjected to 20‐min ischemia. Adenosine treatment reduced postischemic lactate dehydrogenase efflux (indicating necrosis) from 24±2 to 9±1 IU/g, and postischemic diastolic contracture from 21±2 to 5±2 mm Hg, and enhanced postischemic ventricular pressure development from 72±3 to 135±4 mm Hg. The antinecrotic response was reduced ≈50% by inhibition of protein translation (10 µM cycloheximide, CHX), unaltered by inhibition of transcription (20 µM actinomycin D, Act‐D), and abrogated by mitochondrial KATP channel inhibition (100 µM 5‐hydroxydecanoate, 5‐HD). In contrast, protection against contractile dysfunction was reduced but not eliminated by CHX, Act‐D, and 5‐HD, and inhibitory effects CHX and Act‐D were not additive with those of 5‐HD, supporting a common mechanistic path. Inhibitory effects of Act‐D were mimicked by 1.5 µM α‐amanitin. These data provide evidence that adenosine limits necrosis in a mito KATP channel‐dependent manner involving protein translation. The translational component is not dependent upon mRNA transcription. Adenosine also substantially reduces contractile dysfunction via a pathway involving mitochondrial KATP channel activation, protein translation, and mRNA transcription. Protection independent of this path was also evident. Thus, distinct signaling pathways appear to be involved in adenosine‐mediated protection against postischemic necrosis and contractile dysfunction. Drug Dev. Res. 58:454–460, 2003. © 2003 Wiley‐Liss, Inc.
Immunological characterization of A2B adenosine receptors in human mast cells
Authors: Feoktistov Igor , Goldstein Anna , Sheller James R. , Schwartz Lawrence B. , Biaggioni Italo
Published: May 2003

There is increasing evidence that adenosine modulates mast cell function. Such an interaction may be particularly important in asthma. Inhaled adenosine provokes bronchoconstriction in asthmatic patients through processes associated with mast cell activation. The adenosine receptor type that mediates these actions has not been identified. For this purpose, we generated antibodies against a 22‐mer peptide corresponding to C‐terminus of the human A2B adenosine receptor. This antibody recognized adenosine A2B receptors on Western blots as a band with an apparent molecular mass of 31kDa, and a smear of immunoreactivity in the region from 60 to 130kDa. Enzymatic deglycosylation of adenosine A2B receptor, or prevention of natural glycosylation with tunicamycin resulted in accumulation of protein with an apparent molecular mass of 29kDa. The specificity of this antibody was confirmed in experiments with HA‐tagged A2B receptor fusion protein. Anti‐HA and anti‐A2B antibodies, used for immunoprecipitation and Western blotting of the fusion protein, labeled the same glycoprotein in membranes of transfected, but not mock‐transfected cells. These antibodies were also found useful in immunocytochemistry, as evidenced by specific staining of cells expressing A2B, but not other subtypes of adenosine receptors. Human lung mast cells obtained from bronchoalveolar lavage fluid of asthmatic patients were identified by specific monoclonal anti‐tryptase antibody. Double immunostaining demonstrated expression of A2B receptors in tryptase‐positive cells. Our results, therefore, demonstrate the presence of A2B receptors in human lung mast cells and support the hypothesis that A2B receptors are involved in activation of mast cells in asthma. Drug Dev. Res. 58:461–471, 2003. © 2003 Wiley‐Liss, Inc.
Intracellular phosphorylation of chloro‐adenosine analogs is a prerequisite for activation of caspase‐3 and induction of apoptosis in human astrocytoma cells
Authors: Ceruti Stefania , Mazzola Alessia , Beltrami Elena , Passera Davide , Piantoni Elena , Cattabeni Flaminio , Abbracchio Maria P.
Published: May 2003

We previously demonstrated that both Cladribine (2‐chloro‐deoxyadenosine) and the related compound 2‐chloroadenosine induce apoptosis of human astrocytoma cells (Ceruti et al. [2000] J Neurosci Res 60:388–400). In the present study we have characterized the role of the most important “effector” caspase (caspase‐3) in the same experimental model and the relationship between the intracellular phosphorylation of the two adenosine analogs and activation of this enzyme. Data show that: 1) both adenosine analogs can activate caspase‐3 in a time‐dependent fashion; 2) significant activation of the enzyme (i.e., 6–7‐fold over control level) can be detected before any appearance of nuclear signs of apoptosis; 3) the degree of caspase‐3 activation is proportional to the percentage of apoptosis at the end of the incubation period, suggesting a causal relationship between enzyme activation and induction of cell death; and 4) both activation of caspase‐3 and induction of cell death can be completely prevented by preexposure of cultures to inhibitors of the intracellular phosphorylation of 2‐chloroadenosine and 2‐chloro‐2′‐deoxyadenosine (namely, 5‐iodotubercidin and 2′‐deoxycytidine, respectively). Adenosine analogs act, therefore, as prodrugs and the toxic species are represented by the corresponding chloro‐nucleotides. The pathways upstream of caspase‐3 activation in human astrocytoma cells still remain to be elucidated. Taken together, these data strongly suggest a possible use of adenosine analogs in the pharmacological treatment of central nervous system tumors and of all tumors characterized by a high activity of nucleoside kinases leading to selective intracellular accumulation of toxic chloro‐nucleotides. Drug Dev. Res. 58:396–404, 2003. © 2003 Wiley‐Liss, Inc.
Dissecting the regulatory mechanisms controlling inhibitory adenosine receptor signaling
Authors: Palmer Timothy M. , Ferguson Gail , Watterson Kenneth R.
Published: May 2003

The ability of target cells to respond to rapid changes in extracellular adenosine concentrations that occur in response to ischemia is determined by their complement of adenosine receptors. Four adenosine receptor subtypes, termed A1, A2A, A2B, and A3, have been identified by pharmacological and molecular cloning studies. In addition to displaying distinct pharmacological characteristics, each receptor mediates its intracellular effects by coupling to defined G‐protein families. Our studies have concentrated on applying a combination of molecular biological, biochemical, and cell biological approaches to define the molecular mechanisms by which adenosine receptor‐derived signaling events are regulated. These studies have revealed that the desensitization of closely related adenosine receptors, which bind the same agonist in vivo (i.e., adenosine) and activate the same family of G proteins, is mediated by unique receptor‐specific mechanisms. In this review, the nature of these differences, and how they could potentially be exploited to test novel strategies for enhancing the cardioprotective effects of inhibitory adenosine receptor activation in vivo, will be described. Drug Dev. Res. 58:302–314, 2003. © 2003 Wiley‐Liss, Inc.
Adenosine A3 receptors in the rat hippocampus: Lack of interaction with A1 receptors
Authors: Lopes Luísa V. , Rebola Nelson , Costenla Ana Rita , Halldner Linda , Jacobson Marlene A. , Oliveira Catarina R. , Richardson Peter J. , Fredholm Bertil B. , Ribeiro Joaquim A. , Cunha Rodrigo A.
Published: May 2003

Adenosine acts as a neuromodulator in the hippocampus essentially through activation of inhibitory A1 receptors. Using single‐cell PCR analysis, we found that CA1 pyramidal cells coexpress A1 receptor mRNA together with that of another adenosine receptor, the A3 receptor. As occurs for the A1 receptor, Western blot analysis indicated that the A3 receptor is also located in hippocampal nerve terminals. However, activation of A3 receptors with its purportedly selective agonist Cl‐IBMECA (0.1–10 µM) failed to affect hippocampal synaptic transmission or to modify the evoked release of glutamate or GABA. Also, blockade of A3 receptors with MRS 1191 (5 µM) failed to affect either hypoxia‐ or ischemia‐induced depression of hippocampal synaptic transmission. Activation of A3 receptors also failed to control A1 receptor function, as Cl‐IBMECA (100 nM) did not modify the ability of CPA to displace [3H]DPCPX binding to hippocampal membranes or the A1 receptor‐mediated inhibition of hippocampal synaptic transmission. However, ligand binding studies revealed that Cl‐IBMECA displaced the binding of an A1 receptor agonist ([3H]R‐PIA, Ki=47 nM) or antagonist ([3H]DPCPX, Ki=130 nM), which suggests that A3 receptor ligands also act on native A1 receptors. We believe that A3 receptors are expressed in hippocampal neurons and are located in hippocampal nerve terminals, though their function remains elusive. Drug Dev. Res. 58:428–438, 2003. © 2003 Wiley‐Liss, Inc.
Cardioprotection with pre‐ and postischemic adenosine and A3 receptor activation: Differing mechanisms and effects on necrosis versus stunning
Authors: Flood Amanda , Willems Laura , Headrick John P.
Published: May 2003

The importance of pre‐ versus postischemic treatment in adenosine‐mediated cardioprotection is unclear. We characterized effects of pre‐ and postischemic adenosine or A3 adenosine receptor (A3AR) agonism in Langendorff perfused mouse hearts subjected to 20 min global ischemia and 45 min reperfusion. In untreated hearts, diastolic pressure remained elevated at 21±2 mmHg, ventricular pressure development recovered to 75±3 mmHg (50% of pre‐ischemia), and 24±3 IU/ lactate dehydrogenase (LDH) was lost. Adenosine (50 µM) treatment prior to ischemia reduced LDH efflux by 40% (15±2 IU/g) yet exerted only modest effects on recovery of force (83±2 mmHg). Additional treatment during the first 15 min reperfusion was no more effective in reducing LDH efflux (14±2 IU/g) but further limited contractile dysfunction (93±2 mmHg). Continued treatment throughout 45 min reperfusion most effectively limited LDH efflux (10±1 IU/g) and contractile dysfunction (124±6 mmHg). Some protection was also observed with treatment during reperfusion only (16±1 IU/g and 106±3 mmHg). Effects of pre‐ and postischemic adenosine on necrosis and contractile dysfunction were not mimicked by pre‐ and postischemic A3AR agonism with 100 nM 2‐chloro‐N6‐(3‐iodobenzyl)‐adenosine‐5′‐N‐methyluronamide (Cl‐IB‐MECA), or mitochondrial KATP channel activation with 50 µM diazoxide. Protection with Cl‐IB‐MECA and diazoxide was less than with adenosine, maximal with treatment during ischemia alone, and absent with treatment during reperfusion alone. Data indicate antinecrotic effects of adenosine are primarily mediated prior to and during ischemia and are consistent with A3AR and mitochondrial KATP channel activation. In contrast, protection against contractile dysfunction involves other mechanisms and is enhanced with prolonged postischemic treatment. Drug Dev. Res. 58:447–453, 2003. © 2003 Wiley‐Liss, Inc.
Nucleotides and dinucleotides in ocular physiology: New possibilities of nucleotides as therapeutic agents in the eye
Authors: Pintor Jesús , Peral Assumpta , Peláez Teresa , Carracedo Gonzalo , Bautista Alfredo , Hoyle Charles H. V.
Published: May 2003

Nucleotides and dinucleotides have interesting physiological actions in the eye. The involvement of these naturally occurring substances in processes such as tear secretion, intraocular pressure, corneal wound healing, or retinal detachment is discussed. Nucleotides are present in rabbit and human tears and they exert interesting effects, such as increasing tear secretion and augmenting the rate of re‐epithelialisation. Nucleotides and dinucleotides are present in the aqueous humour, and they can modify the production or drainage of the aqueous humour and therefore affect the intraocular pressure. In the retinal space, nucleotides can modify the activity of both neuronal and glial retinal elements in different ways. Some chemically modified nucleotides and dinucleotides can be more active than the natural ones, opening up the possibility of using them for clinical purposes. In particular, compounds designed for dry eye syndrome, ocular hypertension, and retinal detachment are under study with very promising results. In summary, these compounds are becoming more relevant to the understanding of ocular physiology and also as a novel strategy for the treatment of ocular pathologies. Drug Dev. Res. 59:136–145, 2003. © 2003 Wiley‐Liss, Inc.
Modeling the response of the asthmatic airways to adenosine: Mechanisms and receptors
Authors: Fozard John R. , Tigani Bruno , Wolber Cedric , Williams Iwan , Mazzoni Lazzaro , Hannon Jason P.
Published: May 2003

We describe a new experimental animal model which mimics closely the bronchoconstrictor effects of adenosine in asthmatics. Brown Norway (BN) rats were sensitized to ovalbumin (OA). Subsequent challenge with OA induced a marked and selective airway hyperresponsiveness to adenosine. The augmented response to adenosine was blocked selectively by disodium cromoglycate, methysergide, and theophylline and associated with increases in the plasma concentrations of histamine and 5‐HT and degranulation of airway mast cells. The broad‐spectrum adenosine receptor agonist, NECA, also induced bronchoconstriction in actively sensitized (AS), OA‐challenged animals, whereas agonists selective for A1, A2A, and A3 receptors induced minimal effects. MRS 1754, which has similar affinity for rat A2B and A1 receptors, failed to block the response to adenosine, despite blocking the A1 receptor‐mediated bradycardia‐induced by NECA. 8‐SPT and CGS 15943, antagonists at A1, A2A, and A2B but not A3 receptors, inhibited the bronchoconstrictor response to adenosine by 3‐fold but only at doses yielding plasma concentrations 139 and 21 times greater than their respective KB values at the rat A2B receptor. Adenosine and NECA, but not CPA, CGS 21680, or 2‐Cl‐IB‐MECA, induced contraction of parenchymal strip preparations from AS, OA‐challenged animals. Responses to adenosine could not be antagonized by 8‐SPT or MRS 1754 at concentrations≥50 times their affinities at the rat A2B receptor. Upregulation by allergic activation, mast cell dependency, and selective blockade by theophylline represent striking similarities between the bronchoconstrictor response to adenosine in the BN rat and that on the airways of asthmatics. However, the receptor mediating the response in the rat cannot be categorized as one of the four recognized adenosine receptor subtypes. Drug Dev. Res. 59:23–29, 2003. © 2003 Wiley‐Liss, Inc.
P2Y receptors: New subtypes, new functions
Authors: Boeynaems Jean‐Marie , Wilkin Françoise , Marteau Frédéric , Duhant Xavier , Savi Pierre , Suarez Gonzalez Nathalie , Robaye Bernard , Communi Didier
Published: May 2003

The orphan receptor GPR86 was recently identified as a new ADP receptor coupled to Gi and named P2Y13. This brings to eight the number of genuine P2Y receptors. On the basis of sequence homology, they can be subdivided into two subgroups: P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11; and P2Y12, P2Y13, and the UDP‐glucose receptor that should be renamed P2Y14. Some pharmacological properties of the P2Y13 receptor are significantly different from those of the P2Y12 receptor:

• ATP and 2MeSATP behaved as weak partial agonists.

• Potency of 2MeSADP was greater than or equal to that of ADP, depending on the expressing cell line and signaling pathway studied.

• AR‐C67085MX behaved as an antagonist, but only with a µM potency as compared to nM at the P2Y12 receptor.

• The active metabolite of clopidogrel had no effect.

Expression of P2Y13 mRNA was highest in brain, spleen, and various types of leukocytes, in particular dendritic cells. Recent results underscore the role of other P2Y receptors, especially P2Y11, in dendritic cell biology. Indeed, ATP and other nucleotides have multiple effects on human dendritic cells: potentiation of maturation, potentiation, or inhibition of IL‐12p40 secretion (depending on the level of stimulation), inhibition of IL‐12p70 production, potentiation of IL‐10 secretion, and modulation of the repertoire of expressed chemokines and chemokine receptors. These actions are mediated by a rise in cAMP and the rank order of potency of various nucleotides is consistent with the involvement of the P2Y11 receptor. On the other hand, several nucleotides inhibit the proliferation of human CD4+ T‐cells and their secretion of cytokines: these actions also involve a rise in cAMP, apparently mediated by a receptor other than P2Y11. These actions are reminiscent of those of PGE2 and might represent a protective mechanism operating during an exaggerated inflammatory response, when large amounts of nucleotides are released from damaged and dying cells. Drug Dev. Res. 59:30–35, 2003. © 2003 Wiley‐Liss, Inc.
Signalling pathways and ion channel regulations of P2Y receptors
Authors: Barnard Eric A. , Simon Joseph , Tsim Karl W.K. , Filippov Alexander K. , Brown David A.
Published: May 2003

The P2Y receptors form a particularly diverse family of nucleotide receptors, whose current status is briefly reviewed here. A recent addition, the P2Y12 receptor, is of particular interest for its significance for blood coagulation and for some unusual behaviour of its ligand potencies. Strong antagonists for it in the platelet can become strong agonists in its recombinant expression. We have cloned it also from a capillary endothelial cell line, again with similar variation from the behaviour in the platelet. The P2Y receptors are shown to couple to several types of ion channels, as significant new transductions for them. Comparison between subtypes in these properties is illuminating. The downstream signalling of the P2Y1 receptor has been studied and these properties are considered, with an approach to comparing native and recombinant transduction behaviours. Evidence for a role of the P2Y1 receptor in synaptogenesis is also presented, with actions at the level of gene transcription. Drug Dev. Res. 59:36–48, 2003. © 2003 Wiley‐Liss, Inc.
ATP induced three types of pain behaviors, including allodynia
Authors: Inoue Kazuhide , Tsuda Makoto , Koizumi Schuichi
Published: May 2003

ATP excites dorsal root ganglion (DRG) neurons in the nociceptive signaling pathway via ATP‐gated cation channels (P2X receptors). ATP and its analog α,β‐methylene ATP (αβmeATP) activated two types of inward currents; one is a rapidly desensitizing current which is observed in capsaicin (CAP)‐sensitive DRG neurons and in C6BU‐1 cells expressing homomeric P2X3 receptors. The other is a slowly desensitizing current which is seen in CAP‐insensitive medium‐sized DRG neurons and in C6BU‐1 expressing heteromeric P2X2/3 receptors. These findings suggest that P2X3 and P2X2/3 are involved in the generation or modulation of pain. To clarify this hypothesis, we investigated the effects of agonists for P2X receptors on pain sensitivities using a behavioral approach. Activation of P2X receptors at a peripheral site by the injection of ATP or αβmeATP into the hindpaw produced three distinct types of pain‐related behaviors (nocifensive behavior, thermal hyperalgesia, and mechanical allodynia). Nocifensive behavior and thermal hyperalgesia were blocked by pretreatment with PPADS and were not observed in neonatal CAP‐treated adult rats that had selectively lost CAP‐sensitive neurons. The αβmeATP‐induced allodynia was sensitive to PPADS, was a relatively long‐lasting response, and remained in neonatal CAP‐treated adult rats. Furthermore, while pretreatment by P2X3 antisense oligodeoxynucleotide (ODN) diminished all three pain responses, P2X2 antisense ODN inhibited only the mechanical allodynia. These findings suggests that activation of homomeric P2X3 receptors in peripheral terminals of CAP‐sensitive primary afferent fibers plays a role in the induction of nocifensive behavior and thermal hyperalgesia and that activation of heteromeric P2X2/3 receptors in CAP‐insensitive fibers leads to the induction of mechanical allodynia. Drug Dev. Res. 59:56–63, 2003. © 2003 Wiley‐Liss, Inc.
Flavonoids — novel lead compounds for the development of P2Y2 receptor antagonists
Authors: Kaulich Marko , Streicher Franziska , Mayer Ralf , Müller Ingrid , Müller Christa E.
Published: May 2003

A series of 40 flavonoids were investigated as antagonists at P2Y2 receptors expressed in NG108‐15 cells (mouse neuroblastoma×rat glioma hybrid cell line) in a functional assay measuring the inhibition of UTP‐stimulated intracellular calcium release. Several flavonoids were identified as potent antagonists at P2Y2 receptors with IC50 values in the low micromolar concentration range; they were similarly potent or more potent than the standard P2Y2 antagonists Reactive Blue 2 and suramin. Flavone derivatives proved to be more potent than flavanones. The flavone derivatives catechin and epicatechin were inactive. However, a bicyclic benzopyranone ring system was found to be not an absolute prerequisite for P2Y2 antagonism, since the chalcone derivative β‐oxo‐aurentiacin (14) was also relatively potent (IC50 19 µM). Investigated flavone glycosides were completely inactive. The most potent P2Y2 receptor antagonists of the present series were kaempferol (19), heptamethoxyflavon (29), and tangeretin (25), with IC50 values between 6–19 µM. Increased lipophilicity by introducing (additional) methyl groups did not generally increase antagonistic potency. Structure–activity relationships proved to be complex. Concentration–response curves for the P2Y2 agonist UTP were not shifted to the right in the presence of increasing concentrations of tangeretin (25), and EC50 values for UTP were not affected by the antagonist, but the amplitude of the response was reduced, indicating allosteric antagonism. In conclusion, we have identified flavonoids as novel lead structures for the development of noncompetitive antagonists at P2Y2 receptors, which may be of interest as potential antiinflammatory drugs. Drug Dev. Res. 59:72–81, 2003. © 2003 Wiley‐Liss, Inc.