Neuropeptide Y: Direct vasoconstrictor and facilitatory effects on P2X1 receptor-dependent vasoconstriction in human small abdominal arteries.

Neuropeptide Y (NPY) is co-released with norepinephrine and ATP by sympathetic nerves innervating arteries. Circulating NPY is elevated during exercise and cardiovascular disease, though information regarding the vasomotor function of NPY in human blood vessels is limited. Wire myography revealed NPY directly stimulated vasoconstriction (EC50 10.3 ± 0.4 nM; N = 5) in human small abdominal arteries. Maximum vasoconstriction was antagonised by both BIBO03304 (60.7 ± 6%; N = 6) and BIIE0246 (54.6 ± 5%; N = 6), suggesting contributions of both Y1 and Y2 receptor activation, respectively. Y1 and Y2 receptor expression in arterial smooth muscle cells was confirmed by immunocytochemistry, and western blotting of artery lysates. α,ß-meATP evoked vasoconstrictions (EC50 282 ± 32 nM; N = 6) were abolished by suramin (IC50 825 ± 45 nM; N = 5) and NF449 (IC50 24 ± 5 nM; N = 5), suggesting P2X1 mediates vasoconstriction in these arteries. P2X1, P2X4 and P2X7 were detectable by RT-PCR. Significant facilitation (1.6-fold) of α,ß-meATP-evoked vasoconstrictions was observed when submaximal NPY (10 nM) was applied between α,ß-meATP applications. Facilitation was antagonised by either BIBO03304 or BIIE0246. These data reveal NPY causes direct vasoconstriction in human arteries which is dependent upon both Y1 and Y2 receptor activation. NPY also acts as a modulator, facilitating P2X1-dependent vasoconstriction. Though in contrast to the direct vasoconstrictor effects of NPY, there is redundancy between Y1 and Y2 receptor activation to achieve the facilitatory effect.

Giardia duodenalis trophozoites triggered bovine neutrophil extracellular traps formation dependent on P2X1 receptor and PAD4 in vitro.

Giardia duodenalis is an important intestinal protozoan parasite, infections of which are frequently seen in cattle and cause intermittent diarrhea and weight loss in young animals around the world. The release of neutrophil extracellular traps (NETs) is an effector mechanism of neutrophils to fight against invading pathogens including parasites. In this present study, we aimed to investigate the effect of Giardia duodenalis trophozoites on bovine NETs formation, and to further examine its basic characteristics and molecular mechanisms. Scanning electron microscopy analyses displayed that Giardia duodenalis trophozoites exposure triggered NET-like filamentary structures released by bovine polymorphonuclear leukocytes (PMNs), and many trophozoites were entrapped within these structures. Immunofluorescence analyses illustrated that these structures were mainly composed of DNA, histones, Myeloperoxidase (MPO) and neutrophil elastase (NE), which confirmed the classical characteristics of NETs. NETs quantification showed that Giardia duodenalis trophozoites significantly increased NETs formation, and it is in a dose-dependent manner from 4:1-1:2 ratio of PMN: trophozoites. Furthermore, pharmacological inhibitory experiment indicated that P2X1 receptor and PAD4 were essential for Giardia duodenalis trophozoites-triggered NETs formation. Additionally, LC3B-based immunostaining analyses revealed that autophagy and NETs formation occurred simultaneously in Giardia duodenalis trophozoites-exposed bovine PMN, imply that autophagy may play a key role in Giardia duodenalis trophozoites-triggered bovine NETs. In summary, these findings suggest that NETs formation might have a crucial role in innate host defense against Giardia duodenalis trophozoites. Hence, we call for future molecular investigations not only on Giardia duodenalis trophozoites-triggered NETs but also on its potential role in giardiasis-related pathology in vivo.

Novel evidence that the P2X1 purinergic receptor-Nlrp3 inflammasome axis orchestrates optimal trafficking of hematopoietic stem progenitors cells.

INTRODUCTION: Our previous research demonstrated P2X purinergic receptors as important extracellular adenosine triphosphate (eATP) sensing receptors promoting the trafficking of hematopoietic stem progenitor cells (HSPCs). Accordingly, mice deficient in expression of P2X4 and P2X7 receptors turned out to mobilize poorly HSPCs. Similarly, defective expression of these receptors on transplanted HSPCs or in the bone marrow (BM) microenvironment of graft recipient mice led to defective homing, engraftment, and delayed hematopoietic reconstitution. This correlated with decreased activation of intracellular pattern recognition receptor Nlrp3 inflammasome. The P2X receptor family consists of seven purinergic receptors (P2X1-7) and we noticed that in addition to P2X4 and P2X7, HSPCs also highly express rapidly signaling the P2X1 receptor. Therefore, we asked if P2X1 receptor is also involved in HSPCs trafficking. MATERIAL AND METHODS: We employed in vitro and in vivo murine models to study the role of P2X1 receptor blocked on HSPCs or bone marrow microenvironment cells by specific small molecular inhibitor NF499. First, we performed in vitro cell migration assays of bone marrow mononuclear cells (BMMNCs) isolated from normal mice that were exposed to NF499 and compared them to unexposed control cells. Next, in experiments in vivo we mobilized mice exposed to NF499 with G-CSF or AMD3100 and compared mobilization to control unexposed animals. Flow cytometry was employed to identify cell populations and clonogenic assays to enumerate the number of mobilized clonogenic progenitors. Similarly, in homing and engraftment experiments BMMNCs or recipient mice were exposed to NF499 and we evaluated homing and engraftment of transplanted cells by enumerating the number of cells labeled with fluorochromes in recipient mice BM and by evaluating the number of clonogenic progenitors in BM and spleen 24 hours and 12 days after transplantation. We also evaluated the potential involvement of Nlrp3 inflammasome in P2X1 receptor-mediated HSPCs trafficking. RESULTS: We report that the functional P2X1 receptor is highly expressed on murine and human HSPCs. We could demonstrate that the P2X1 receptor promotes the trafficking of murine cells in Nlrp3 inflammasome-dependent manner. Mice after exposure to P2X1 receptor inhibitor poorly mobilized HSPCs from the bone marrow into the peripheral blood. Mice transplanted with BMNNCs exposed to NF499 or recipient mice pretreated with this inhibitor demonstrated defective homing and engraftment as compared to control animals transplanted with cells not exposed to P2X1 inhibitor. Similar effects were noticed for control recipient mice that were not exposed to NF499. CONCLUSIONS: This study demonstrates for the first time the novel role of the P2X1 receptor in HSPCs trafficking in the mouse. Furthermore, it supports an important role of purinergic signaling engaging its downstream target Nlrp3 inflammasome in the mobilization, homing and engraftment of HSPCs.

The P2X1 receptor as a therapeutic target.

Within the family of purinergic receptors, the P2X1 receptor is a ligand-gated ion channel that plays a role in urogenital, immune and cardiovascular function. Specifically, the P2X1 receptor has been implicated in controlling smooth muscle contractions of the vas deferens and therefore has emerged as an exciting drug target for male contraception. In addition, the P2X1 receptor contributes to smooth muscle contractions of the bladder and is a target to treat bladder dysfunction. Finally, platelets and neutrophils have populations of P2X1 receptors that could be targeted for thrombosis and inflammatory conditions. Drugs that specifically target the P2X1 receptor have been challenging to develop, and only recently have small molecule antagonists of the P2X1 receptor been available. However, these ligands need further biological validation for appropriate selectivity and drug-like properties before they will be suitable for use in preclinical models of disease. Although the atomic structure of the P2X1 receptor has yet to be determined, the recent discovery of several other P2X receptor structures and improvements in the field of structural biology suggests that this is now a distinct possibility. Such efforts may significantly improve drug discovery efforts at the P2X1 receptor.

Dysfunction of low-density neutrophils in peripheral circulation in patients with sepsis.

Low-density neutrophils (LDNs) have been described in tumors and various autoimmune diseases, where they exhibit immune dysfunction and alter disease progression. Nevertheless, LDNs have been rarely reported in sepsis. We studied sepsis patients admitted to the intensive care unit. Wright-Giemsa stain assay and Transmission electron microscopy were performed to detect the morphology of neutrophils. Flow cytometry was used to analyze the number and function of LDNs. Concentration of cytokines was measured using ELISA. Neutrophil chemotaxis was examined using an under-agarose chemotaxis model. We found that LDNs were significantly elevated in patients with sepsis. Phenotypes and morphological characteristics suggest that LDNs may be formed by mixtures of neutrophils at various maturation stages. In vitro experiments showed that LDN formation was closely associated with neutrophil degranulation. We preliminarily discussed changes in immune function in LDNs. Compared with high-density neutrophils, expression levels of CXC chemokine receptor 4 on LDN surfaces were increased, phagocytotic capacity was decreased, and life span was prolonged. The chemotactic ability of LDNs was significantly reduced, possibly related to the increased expression of P2X1. These data suggest that LDNs are essential components of neutrophils in sepsis. To clarify the source and dysfunction mechanism of LDN in sepsis may be helpful for the diagnosis and treatment of sepsis in the future.

Regulation of P2X1 receptors by modulators of the cAMP effectors PKA and EPAC.

P2X1 receptors are adenosine triphosphate (ATP)-gated cation channels that are functionally important for male fertility, bladder contraction, and platelet aggregation. The activity of P2X1 receptors is modulated by lipids and intracellular messengers such as cAMP, which can stimulate protein kinase A (PKA). Exchange protein activated by cAMP (EPAC) is another cAMP effector; however, its effect on P2X1 receptors has not yet been determined. Here, we demonstrate that P2X1 currents, recorded from human embryonic kidney (HEK) cells transiently transfected with P2X1 cDNA, were inhibited by the highly selective EPAC activator 007-AM. In contrast, EPAC activation enhanced P2X2 current amplitude. The PKA activator 6-MB-cAMP did not affect P2X1 currents, but inhibited P2X2 currents. The inhibitory effects of EPAC on P2X1 were prevented by triple mutation of residues 21 to 23 on the amino terminus of P2X1 subunits to the equivalent amino acids on P2X2 receptors. Double mutation of residues 21 and 22 and single mutation of residue 23 also protected P2X1 receptors from inhibition by EPAC activation. Finally, the inhibitory effects of EPAC on P2X1 were also prevented by NSC23766, an inhibitor of Rac1, a member of the Rho family of small GTPases. These data suggest that EPAC is an important regulator of P2X1 and P2X2 receptors.

Targeting Purinergic Receptor P2RX1 Modulates Intestinal Microbiota and Alleviates Inflammation in Colitis.

Inflammatory bowel disease (IBD) remains one of the most prevalent gastrointestinal diseases worldwide. Purinergic signaling has emerged as a promising therapeutic target of inflammation-associated diseases. However, little is known about the specific roles of purinergic receptors in IBD. In the present study, expression profile of purinergic receptors was screened in the public Gene Expression Omnibus (GEO) datasets, and we found that expression of P2RX1 was significantly upregulated in inflamed colon tissues. Then, purinergic receptor P2RX1 was genetically ablated in the background of C57BL/6 mice, and dextran sulfate sodium (DSS) was used to induce mice colitis. RNA sequencing results of colon tissues showed that genetic knockout of P2RX1 suppressed the inflammation responses in DSS-induced mice colitis. Flow cytometry indicated that neutrophil infiltration was inhibited in P2RX1 ablated mice. 16S ribosomal DNA sequencing revealed major differences of intestinal microbiota between WT and P2RX1 ablated mice. Functional metagenomics prediction indicated that the indole alkaloid biogenesis pathway was upregulated in P2RX1 gene ablated mice. Further studies revealed that microbiota metabolites (indole alkaloid)-involved aryl hydrocarbon receptor (AhR)/IL-22 axis was associated with the beneficial effects of P2RX1 ablation. Finally, we found that a specific P2RX1 inhibitor succeeded to improve the therapeutic efficiency of anti-TNF-α therapy in DSS-induced mice colitis. Therefore, our study suggests that targeting purinergic receptor P2RX1 may provide novel therapeutic strategy for IBD.

Targeting P2RX1 alleviates renal ischemia/reperfusion injury by preserving mitochondrial dynamics.

Renal ischemia/reperfusion injury (IRI) is the major cause of acute kidney injury. However, mechanisms underlying the sudden loss in kidney function and tissue injury remain to be fully elucidated. Here, we performed RNA sequencing to systematically compare the transcriptome differences between IR injured kidneys and sham kidneys. We observed that mitochondrial dynamics was destructed in renal IRI. Expression of mitochondrial fusion-associated genes was reduced, whereas expression of mitochondrial fission-related genes was increased in renal IRI, and these findings were further confirmed by mitochondrial morphological observations. By screening 19 purinergic receptors, we noticed that P2RX1 expression was markedly upregulated in renal IRI. RNA sequencing and mitochondrial morphological observations revealed that mitochondrial dynamics was preserved in P2RX1 genetic knockout (P2rx1-/-) mice. Neutrophil extracellular traps (NETs) were reported to be essential for tissue injury in renal IRI, but the detailed mechanism remained unclear. In the present study, we found that P2RX1 favored the formation of neutrophil extracellular traps (NETs) in IRI, and NETs was essential for the impairment of mitochondrial dynamics. Mechanistically, P2RX1-involved metabolic interaction between platelets and neutrophils supported NETs formation. Activation of P2RX1 promoted platelets ATP release, which subsequently contributed to neutrophil glycolytic metabolism and NETs generation.

Bongkrekic acid induced neutrophil extracellular traps via p38, ERK, PAD4, and P2X1-mediated signaling.

Bongkrekic acid (BKA) produced by pseudomonas cocovenenans is a deadly toxin, and is mainly found in spoiled or fermented foods. However, less is known on its immunotoxicity. Neutrophil extracellular traps (NETs) are a novel effector mechanism of neutrophils against invading pathogens, but excessive NETs also contribute to tissue damage. This study aimed to investigate NET formation triggered by BKA in murine neutrophils, and describe its characteristics and potential mechanisms. Our results showed that BKA triggered NET formation via co-localization of DNA and histone or MPO by immunostaining. Moreover, BKA-triggered NET formation was dose- and time-dependent via NET quantification based on Picogreen-derived fluorescence intensities. Furthermore, BKA increased ROS production in neutrophils. Pharmacological inhibition indicated that BKA-triggered NET formation was associated with ROS-p38 and -ERK signaling pathways, but independent on NADPH oxidase. Besides, PAD4 and P2X1 receptor also mediated BKA-triggered NET formation. To our knowledge, all these findings provide for the first time an initial understanding of BKA on innate immunity, which might be helpful for further investigation on BKA immunotoxicity.

P2X1: a unique platelet receptor with a key role in thromboinflammation.

Thromboinflammation involves complex interactions between actors of inflammation and immunity and components of the hemostatic system, which are elicited upon infection or tissue injury. In this context, the interplay between platelets and innate immune cells has been intensively investigated. The ATP-gated P2X1 ion channel, expressed on both platelets and neutrophils is of particular interest. On platelets, this ion channel contributes to platelet activation and thrombosis, especially under high shear stress conditions of small arteries, whereas on neutrophils, it is involved in chemotaxis and in mitigating the activation of circulating cells. In vitro studies indicate that it may also be implicated in platelet-dependent immune responses during bacterial infection. More recently, in a mouse model of intestinal epithelial barrier disruption causing systemic inflammation, it has been reported that neutrophil P2X1 ion channel could play a protective role against exaggerated inflammation-associated thrombosis. This review will focus on this unique role of the ATP-gated P2X1 ion channel in thromboinflammation, highlighting possible implications and pointing to the need for further investigation of the role of P2X1 ion channels in the interplay between platelets and neutrophils during thrombus formation under various sterile or infectious inflammatory settings and in distinct vascular beds.

Neuropeptide Y facilitates P2X1 receptor-dependent vasoconstriction via Y1 receptor activation in small mesenteric arteries during sympathetic neurogenic responses.

ATP, norepinephrine and NPY are co-released by sympathetic nerves innervating arteries. ATP elicits vasoconstriction via activation of smooth muscle P2X receptors. The functional interaction between neuropeptide Y (NPY) and P2X receptors in arteries is not known. In this study we investigate the effect of NPY on P2X1-dependent vasoconstriction in mouse mesenteric arteries. Suramin or P2X1 antagonist NF449 abolished α,ß-meATP evoked vasoconstrictions. NPY lacked any direct vasoconstrictor effect but facilitated the vasoconstrictive response to α,ß-meATP. Mesenteric arteries expressed Y1 and Y4 receptors, but not Y2 or Y5. Y1 receptor inhibition (BIBO3304) reversed NPY facilitation of the α,ß-meATP-evoked vasoconstriction. L-type Ca2+ channel antagonism (nifedipine) had no effect on α,ß-meATP-evoked vasoconstrictions, but completely reversed NPY facilitation. Electrical field stimulation evoked sympathetic neurogenic vasoconstriction. Neurogenic responses were dependent upon dual α1-adrenergic (prazosin) and P2X1 (NF449) receptor activation. Y1 receptor antagonism partially reduced neurogenic vasoconstriction. Isolation of the P2X1 component by α1-adrenergic blockade allowed faciliatory effects of Y1 receptor activation to be explored. Y1 receptor antagonism reduced the P2X1 receptor component during neurogenic vasoconstriction. α1-adrenergic and P2X1 receptors are post-junctional receptors during sympathetic neurogenic vasoconstriction in mesenteric arteries. In conclusion, we have identified that NPY lacks a direct vasoconstrictor effect in mesenteric arteries but can facilitate vasoconstriction by enhancing the activity of P2X1, following activation by exogenous agonists or during sympathetic nerve stimulation. The mechanism of P2X1 facilitation by NPY involved activation of the NPY Y1 receptor and the L-type Ca2+ channel.

Diabetic bladder dysfunction in T2D KK-Ay mice and its changes in the level of relevant gene expression.

OBJECTIVE: Diabetic bladder dysfunction (DBD) is one of the most common and bothersome complications of diabetes mellitus (DM). The purpose of the present study is to investigate DBD in KK-Ay mice, and to identify the expression of relative genes. METHOD: Totally twenty-seven KK-Ay mice and thirty C57BL/6 J mice, respectively, were randomly divided into 12-, 18-, and 25-week old groups. The weight, water intake, voided volume, the frequency of micturition, fasting blood glucose (FBG), oral glucose tolerance test (OGTT) were measured at varying time points. Maximum bladder volume (MBC), residual volume (RV), bladder compliance (BC), micturition efficiency (VE) and maximum micturition pressure (MVP) were assessed by urodynamic test, and contractile responses to α, ß-methylene ATP, KCl, electrical-field stimulation, carbachol were performed by detrusor smooth muscle strips contractility test. The bladders were stained with hematoxylin and eosin (H&E) and Masson's trichrome to determine bladder wall thickness. Additionally, the mRNA expression of Myosin Va, SLC17A9, P2X1, M3 and M2 were then verified by qRT-PCR. RESULT: The weight, water intake, voided volumes, micturition frequency, FBG, the blood glucose AUC0-2h of KK-Ay mice were significantly increased at three time points. MBC, RV and BC were significantly increased; VE was significantly lower at the age of 18 and 25 weeks in KK-Ay mice; MVP was significantly increased at the age of 25 weeks in KK-Ay mice. In DSM strips contractility test, the amplitude of the spontaneous activity in KK-Ay mice significant increased at 12 weeks and 18 weeks, while both the amplitude and frequency were significantly decreased at the age of 25 weeks. The level of Myosin Va, SLC17A9 and M3 receptor significantly decreased in KK-Ay mice at 12 weeks, while Myosin Va markedly increased at 18 weeks; P2X1 and M2 receptors of KK-Ay mice was significantly increased at all three time points. CONCLUSION: Taken together, this study demonstrates that KK-Ay mice can be a proper model to investigate DBD whose transformation from compensatory state to decompensated state may ascribe to the time-dependent alternations of Myosin Va, SLC17A9, P2X1, M3 and M2 expression levels.

Functional expression of P2X1, P2X4 and P2X7 purinergic receptors in human monocyte-derived macrophages.

This study sought to examine the co-expression of the following purinergic receptor subunits: P2X1, P2X1del, P2X4, and P2X7 and characterize the P2X response in human monocyte-derived macrophages (MDMs). Single-cell RT-PCR shows the presence of P2X1, P2X1del, P2X4, and P2X7 mRNA in 40%, 5%, 20%, and 90% of human MDMs, respectively. Of the studied human MDMs, 25% co-expressed P2X1 and P2X7 mRNA; 5% co-expressed P2X4 and P2X7; and 15% co-expressed P2X1, P2X4, and P2X7 mRNA. In whole-cell patch clamp recordings of human MDMs, rapid application of ATP (0.01 mM) evoked fast current activation and two different desensitization kinetics: 1. a rapid desensitizing current antagonized by PPADS (1 µM), reminiscent of the P2X1 receptor's current; 2. a slow desensitizing current, insensitive to PPADS but potentiated by ivermectin (3 µM), similar to the P2X4 receptor's current. Application of 5 mM ATP induced three current modalities: 1. slow current activation with no desensitization, similar to the P2X7 receptor current, present in 69% of human macrophages and antagonized by A-804598 (0.1 µM); 2. fast current activation and fast desensitization, present in 15% of human MDMs; 3. fast activation current followed by biphasic desensitization, observed in 15% of human MDMs. Both rapid and biphasic desensitization kinetics resemble those observed for the recombinant human P2X1 receptor expressed in oocytes. These data demonstrate, for the first time, the co-expression of P2X1, P2X4, and P2X7 transcripts and confirm the presence of functional P2X1, P2X4, and P2X7 receptors in human macrophages.

Synthesis of 2-phenyl-5,6,7,8-tetrahydroquinoxaline derivatives and screening for P2X1-purinoceptor antagonist activity in isolated preparations of rat vas deferens, for translation into a male contraceptive†.

Sympathetically mediated contractions of smooth muscle cells in the vasa deferentia are mediated by neuronally released adenosine 5'-triphosphate (ATP) and noradrenaline, which stimulate P2X1-purinoceptors and α1A-adrenoceptors, respectively. This process is crucial for sperm transport, as demonstrated in knockout mouse studies where simultaneous genetic deletion of P2X1-purinoceptors and α1A-adrenoceptors resulted in male infertility. We hypothesize that dual pharmacological antagonism of these two receptors could inhibit sperm transport sufficiently to provide a novel nonhormonal method of male contraception. To generate a suitable P2X1-purinoceptor antagonist, substituents were introduced on the phenyl moiety of 2-phenyl-5,6,7,8-tetrahydroquinoxaline to create a series of analogues that were tested for P2X1-purinoceptor antagonism in isolated preparations of rat vas deferens. Novel compounds were initially screened for their ability to attenuate contractile responses to electrical field stimulation (EFS: 60 V, 0.5 ms, 0.2 Hz). The addition of polar substituents to the meta, but not ortho, position markedly increased the inhibition of contractions, as did the addition of both polar and aliphatic substituents to the para position. Di-substituted compounds were also synthesized and tested, resulting in a compound 31 (2-hydroxy, 4-fluoro), which exhibited the greatest potency, with an IC50 of 14 µM (95% confidence limits: 12-16 µM). Additionally, compound 31 noncompetitively antagonized contractions mediated by exogenously administered αß-methylene ATP (10 nM-30 µM) but had no inhibitory effect on contractions mediated by exogenously administered noradrenaline (30 nM-100 µM) or acetylcholine (30 nM-100 µM). These results have contributed to a structure-activity relationship profile for the P2X1-purinoceptor that will inform future designs of more potent antagonists.

Mitochondria-derived ATP participates in the formation of neutrophil extracellular traps induced by platelet-activating factor through purinergic signaling in cows.

Neutrophil extracellular trap (NET) formation eliminates/prevents the spread of infectious agents. Platelet activating factor (PAF) is involved in infectious diseases of cattle because it recruits and activates neutrophils. However, its ability to induce NET release and the role of metabolism in this process is not known. We investigated if inhibition of glycolysis, mitochondrial-derived adenosine triphosphate (ATP) synthesis and purinergic signaling though P2X1 purinoceptors interfered with NET formation induced by PAF. We inhibited bovine neutrophils with 2-deoxy-d-glucose, rotenone, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and NF449 to evaluate PAF-mediated NET extrusion. PAF induced mitochondrial hyperpolarization and triggered extracellular ATP release via pannexin-1. Inhibition of mitochondrial metabolism prevented extracellular ATP release. Inhibition of glycolysis, complex-I activity and oxidative phosphorylation prevented NET formation induced by PAF. Inhibition of P2X1 purinergic receptors inhibited mitochondrial hyperpolarization and NET formation. We concluded that PAF-induced NET release is dependent upon glycolysis, mitochondrial ATP synthesis and purinergic signaling.

Functional atropine sensitive purinergic responses in the healthy rat bladder.

While acetylcholine is regarded to be the main directly contractile transmitter substance in the urinary bladder, interactions with other transmitters likely occur. Presently, the interplay between purinergic and cholinergic signalling was investigated to unravel the involvement of the urothelium and efferent neurons in the functionally important purinergically evoked release of acetylcholine in vitro. Functional characterization of receptor subtypes involved in this interplay was also performed. In vitro organ bath experiments with electrical field stimulation (EFS) or administration of agonist were performed in the absence and presence of the neurotoxin tetrodotoxin (TTX; 5 × 10-7 M) and/or receptor antagonists, in intact and urothelium-denuded full thickness rat bladder strip preparations. Interestingly, functional contractions to ATP (10-6-10-3 M) remained unaffected by TTX, but were significantly lowered in the presence of the muscarinic antagonist atropine (10-6 M). However, in urothelium-denuded strip preparations, this latter phenomenon was not present and the ATP response remained unaltered. To rule out purinergic interference caused by break-down of ATP, experiments were performed in which the stable ATP-analogue αßMeATP (10-7-10-5 M) gave rise to functional atropine-sensitive contractions. Furthermore, contractions to ATP were not affected by P2Y6 purinoceptor blockade (by MRS2578; 10-7, 10-5 M), nor were relaxatory responses to ATP sensitive to atropine, PPADS (3 × 10-5 M) or αßMeATP. Lastly, relaxations to ADP (10-6-10-3 M) or NECA (10-8-10-5 M) were unaltered by the presence of atropine. To conclude, purinergic functional contractile, but not relaxatory, responses are supported by the cholinergic transmitter system in vitro, through non-neuronal mechanisms in the urothelium. Involved purinoceptors are of the P2X-subtype, most likely P2X1 and/or P2X3.

Discovery and Structure Relationships of Salicylanilide Derivatives as Potent, Non-acidic P2X1 Receptor Antagonists.

Antagonists for the ATP-gated ion channel receptor P2X1 have potential as antithrombotics and for treating hyperactive bladder and inflammation. In this study, salicylanilide derivatives were synthesized based on a screening hit. P2X1 antagonistic potency was assessed in 1321N1 astrocytoma cells stably transfected with the human P2X1 receptor by measuring inhibition of the ATP-induced calcium influx. Structure-activity relationships were analyzed, and selectivity versus other P2X receptor subtypes was assessed. The most potent compounds, N-[3,5-bis(trifluoromethyl)phenyl]-5-chloro-2-hydroxybenzamide (1, IC50 0.0192 µM) and N-[3,5-bis(trifluoromethyl)phenyl]-4-chloro-2-hydroxybenzamide (14, IC50 0.0231 µM), displayed >500-fold selectivity versus P2X2 and P2X3, and 10-fold selectivity versus P2X4 and P2X7 receptors, and inhibited collagen-induced platelet aggregation. They behaved as negative allosteric modulators, and molecular modeling studies suggested an extracellular binding site. Besides selective P2X1 antagonists, compounds with ancillary P2X4 and/or P2X7 receptor inhibition were discovered. These compounds represent the first potent, non-acidic, allosteric P2X1 receptor antagonists reported to date.

Purinergic P2X1 receptor, purinergic P2X7 receptor, and angiotensin II type 1 receptor interactions in the regulation of renal afferent arterioles in angiotensin II-dependent hypertension.

In ANG II-dependent hypertension, ANG II activates ANG II type 1 receptors (AT1Rs), elevating blood pressure and increasing renal afferent arteriolar resistance (AAR). The increased arterial pressure augments interstitial ATP concentrations activating purinergic P2X receptors (P2XRs) also increasing AAR. Interestingly, P2X1R and P2X7R inhibition reduces AAR to the normal range, raising the conundrum regarding the apparent disappearance of AT1R influence. To evaluate the interactions between P2XRs and AT1Rs in mediating the increased AAR elicited by chronic ANG II infusions, experiments using the isolated blood perfused juxtamedullary nephron preparation allowed visualization of afferent arteriolar diameters (AAD). Normotensive and ANG II-infused hypertensive rats showed AAD responses to increases in renal perfusion pressure from 100 to 140 mmHg by decreasing AAD by 26 ± 10% and 19 ± 4%. Superfusion with the inhibitor P2X1Ri (NF4490; 1 µM) increased AAD. In normotensive kidneys, superfusion with ANG II (1 nM) decreased AAD by 16 ± 4% and decreased further by 19 ± 5% with an increase in renal perfusion pressure. Treatment with P2X1Ri increased AAD by 30 ± 6% to values higher than those at 100 mmHg plus ANG II. In hypertensive kidneys, the inhibitor AT1Ri (SML1394; 1 µM) increased AAD by 10 ± 7%. In contrast, treatment with P2X1Ri increased AAD by 21 ± 14%; combination with P2X1Ri plus P2X7Ri (A438079; 1 µM) increased AAD further by 25 ± 8%. The results indicate that P2X1R, P2X7R, and AT1R actions converge at receptor or postreceptor signaling pathways, but P2XR exerts a dominant influence abrogating the actions of AT1Rs on AAR in ANG II-dependent hypertension.

P2RX1-Involved Glycolytic Metabolism Supports Neutrophil Activation in Acute Pancreatitis.

Acute pancreatitis (AP) is characterized by disordered inflammation of the pancreas, and the underlying mechanisms remain unclear. Purinergic signaling plays crucial roles in initiating and amplifying inflammatory signals. Recent evidence reveals that targeting dysregulated purinergic signaling is promising for treating inflammation-associated diseases. To explore the potential involvement of purinergic signaling in AP, we investigated the expression profiles of purinergic signaling molecules in human and mouse pancreas tissues. Results showed that purinergic receptor P2RX1 was among the most highly expressed genes in both human and mouse pancreas tissues. Genetic ablation or specific antagonism of P2RX1 markedly alleviated inflammatory responses in caerulein-induced AP mice. Bone marrow chimeras and adoptive transfer studies revealed that neutrophil-derived P2RX1 contributed to the inflammatory responses in AP. Further studies demonstrated that P2RX1 promoted neutrophil activation by facilitating glycolytic metabolism. Therefore, our study indicates that purinergic receptor P2RX1 may be a potential therapeutic target to treat disordered inflammation in AP.

Tonic Calcium-Activated Chloride Current Sustained by ATP Release and Highly Desensitizing Human P2X1 Receptors.

Extracellular adenosine triphosphate (ATP) participates in maintaining the vascular tone in the CNS, particularly in the retina, via the tonic activity of ligand gated activated P2X1 receptors. P2X1 receptors are characterized by their high affinity for ATP and their strong desensitization to concentrations of ATP that are 200-fold lower than their EC50. The mechanism behind P2X1 tonic activity remains unclear. In this study, we expressed human P2X1 (hP2X1) homomeric receptors in Xenopus oocytes to explore the relationship between ATP release from oocytes at rest, hP2X1, and Ca2+-activated Cl- channels. Our results indicate that Xenopus oocytes release ATP at rest via vesicular exocytosis, and this process is a constitutive phenomenon independent of extracellular Ca2+. Our results also indicate that hP2X1 receptors are able to sustain a tonic activity of Ca2+-activated Cl- channels. In the presence of extracellular Ca2+ the activity of hP2X1 receptors is greatly amplified by its coupling with Ca2+-activated Cl- channels. Future studies addressing the relationship between hP2X1 receptors and Ca2+-activated Cl- channels in vascular smooth muscle cells should provide information about additional mechanisms that regulate the vascular tone and their potential as pharmaceutical targets. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.