Prototypic P2X7 Receptor Agonist, BzATP, Induced the Expression of Unfolded Protein Response Genes in Human M1 Macrophages.

Purinergic receptors stimulation by adenosine triphosphate (ATP) contributes significantly to macrophage activation, and also macrophage cell death. Upon the macrophage activation, the protein load of the endoplasmic reticulum is increased which is resulted in the activation of unfolded protein response (UPR). In the current study, we aimed to evaluate the connection between prototypic P2X7 receptor agonist, extracellular 2'(3')-O-(4-Benzoylbenzoyl)-ATP (BzATP), and the UPR pathway in macrophages. The monocyte-derived macrophages from blood samples of 14 healthy volunteers were skewed toward M1 macrophages after incubation with LPS and IFN-γ. M1 macrophages were treated with 200 µM BzATP. The expression levels of UPR genes, including CHOP, HERP, GADD34, XBP1, and ATF6 in macrophages before and after treatment were measured using real-time polymerase chain reaction. The results demonstrated that the expression of CHOP, HERP, and ATF6 is significantly decreased and the expression level of GADD34 and XBP1 is significantly increased after M1 polarization. BzATP not only significantly increased the expression levels of CHOP, GADD34, ATF6, and HERP but also significantly decreases the XBP1 expression level in M1 macrophages. The present study showed that BzATP induces cellular stress in M1 macrophages by elevating the expression levels of UPR genes including CHOP, GADD34, ATF6, and reducing cell viability.

P2X7 receptor in multifaceted cellular signalling and its relevance as a potential therapeutic target in different diseases.

P2X7 receptor, a purinergic receptor family member, is abundantly expressed on many cells, including immune, muscle, bone, neuron, and glia. It acts as an ATP-activated cation channel that permits the influx of Ca2+, Na+ and efflux of K+ ions. The P2X7 receptor plays crucial roles in many physiological processes including cytokine and chemokine secretion, NLRP3 inflammasome activation, cellular growth and differentiation, locomotion, wound healing, transcription factors activation, cell death and T-lymphocyte survival. Past studies have demonstrated the up-regulation and direct association of this receptor in many pathophysiological conditions such as cancer, diabetics, arthritis, tuberculosis (TB) and inflammatory diseases. Hence, targeting this receptor is considered a worthwhile approach to lessen the afflictions associated with the disorders mentioned above by understanding the receptor architecture and downstream signalling processes. Here, in the present review, we have dissected the structural and functional aspects of the P2X7 receptor, emphasizing its role in various diseased conditions. This information will provide in-depth knowledge about the receptor and help to develop apt curative methodologies for the betterment of humanity in the coming years.

Voltage-clamp fluorometry analysis of structural rearrangements of ATP-gated channel P2X2 upon hyperpolarization.

Gating of the ATP-activated channel P2X2 has been shown to be dependent not only on [ATP] but also on membrane voltage, despite the absence of a canonical voltage-sensor domain. We aimed to investigate the structural rearrangements of rat P2X2 during ATP- and voltage-dependent gating, using a voltage-clamp fluorometry technique. We observed fast and linearly voltage-dependent fluorescence intensity (F) changes at Ala337 and Ile341 in the TM2 domain, which could be due to the electrochromic effect, reflecting the presence of a converged electric field. We also observed slow and voltage-dependent F changes at Ala337, which reflect structural rearrangements. Furthermore, we determined that the interaction between Ala337 in TM2 and Phe44 in TM1, which are in close proximity in the ATP-bound open state, is critical for activation. Taking these results together, we propose that the voltage dependence of the interaction within the converged electric field underlies the voltage-dependent gating.

PI3K/Akt/GSK-3ß signal pathway is involved in P2X7 receptor-induced proliferation and EMT of colorectal cancer cells.

P2X7 receptor (P2X7R) plays an important role in regulating the growth of tumor cells. However, the role of P2X7R in colorectal cancer (CRC) has remained poorly understood. Therefore, in this study, in vivo and in vitro experiments were performed to investigate the effect of P2X7R on the proliferation of CRC. The results showed that P2X7R was expressed in CRC cell lines (SW620 and HCT116). ATP and BzATP increased the expression of P2X7R in CRC cells, while the application of P2X7R antagonist A438079 and AZD9056 decreased the P2X7R expression induced by BzATP. Moreover, ATP and BzATP induced the activation of P2X7R to promote the proliferation, migration and invasion of CRC cells. Conversely, A438079, AZD9056 or siRNA transfection targeting P2X7R (siP2X7R) knockdown P2X7R expression inhibited the proliferation and migration of CRC cells. TGF-ß1 promoted the migration and invasion of CRC cells, while the application of P2X7R antagonist could inhibit TGF-ß1 induced migration of CRC cells. Furthermore, activation of P2X7R increased the expression of Vimentin, Snail, Fibronectin and decreased the expression of E-cadherin. While reducing the expression of P2X7R could inhibit these genes expression. In addition, ATP and BzATP increased the expression of p-Akt, p-GSK-3beta and ß-catenin via P2X7R. P13/Akt pathway inhibitor LY294002 inhibited the proliferation of CRC cells, and the P13/Akt signaling was required for BzATP induced the proliferation of CRC cells. Our conclusion is that P2X7R mediated the PI3K/Akt/GSK-3beta signaling to promote the proliferation and EMT of CRC, indicating that P2X7R may be used as a potential therapeutic target for CRC.

P2X receptor agonist enhances tumor-specific CTL responses through CD70+ DC-mediated Th17 induction.

Extracellular ATP is known to promote Th17 cell differentiation in the intestinal lamina propria by stimulating CD70+CD11clow dendritic cells (DCs) via P2X receptors (P2XRs). Recent studies have also shown that Th17 cells enhance antitumor immunity by directly promoting proliferation of cytotoxic T lymphocytes (CTLs). These finding led us to test a P2XR agonist, αß-methylene ATP (αß-ATP), as a mucosal vaccine adjuvant to promote CTL responses through Th17 induction. We demonstrated that (i) CD70+CD11clow DCs were present in the nasal lamina propria and expressed P2X1R, P2X2R and P2X4R; (ii) CD70+CD11clow DCs isolated from the nasal lamina propria enhanced Th17 cell differentiation of cocultured splenic CD4+ T cells upon stimulation with αß-ATP; (iii) mice intranasally immunized with ovalbumin (OVA) and αß-ATP had increased OVA-specific Th17 cells and CTLs in the nasal lamina propria and regional lymph nodes; (iv) mice intranasally immunized with OVA and αß-ATP also had elevated resistance to E.G7-OVA tumor growth compared with those intranasally immunized with OVA alone; (v) suramin, a broad-range inhibitor of P2 receptors, suppressed the increases of OVA-specific Th17 cells and CTLs in mice intranasally immunized with OVA and αß-ATP; and (vi) suramin also abrogated the enhanced antitumor immunity of mice intranasally immunized with OVA and αß-ATP against E.G7-OVA. Collectively, αß-ATP may be a promising mucosal adjuvant that promotes antigen-specific CTL responses via CD70+CD11clow DC-mediated Th17 induction.

Potentiation of P2X3 receptor mediated currents by endothelin-1 in rat dorsal root ganglion neurons.

Endothelin-1 (ET-1), an endogenous vasoconstrictor, has been known as a pro-nociceptive agent involved in multitude of pain. ET-1 acts on endothelin receptors on vascular endothelial cells, sensitizes release of ATP, which then acts on P2X3 receptors on nociceptors and results in mechanical hyperalgesia. Both endothelin receptors and P2X3 receptors are present in primary sensory neuron, where it remains unclear whether there is an interaction between them. Herein, we reported that ET-1 potentiated the electrophysiological activity of P2X3 receptors in rat dorsal root ganglia (DRG) neurons. ET-1 concentration-dependently increased α,ß-methylene-ATP (α,ß-meATP)-evoked inward currents, which were mediated by P2X3 receptors. ET-1 shifted the α,ß-meATP concentration-response curve upwards, with an increase of 34.38 ± 4.72% in the maximal current response to α,ß-meATP in the presence of ET-1. ET-1 potentiation of α,ß-meATP-evoked currents was voltage-independent. ET-1 potentiated P2X3 receptor-mediated currents through endothelin-A receptors (ETAR), but not endothelin-B receptors (ETBR). ET-1 potentiation was supressed by blockade of intracellular G-protein or protein kinase C (PKC) signaling. Moreover, there is a synergistic effect on mechanical allodynia induced by intraplantar injection of ET-1 and α,ß-meATP in rats. Pharmacological blockade of P2X3 receptors also alleviated ET-1-induced mechanical allodynia. These results suggested that ET-1 sensitized P2X3 receptors in primary sensory neurons via an ETAR and PKC signaling pathway. Our data provide evidence that cutaneous ET-1 induced mechanical allodynia not only by increasing the release of ATP from vascular endothelial cells, but also by sensitizing P2X3 receptors on nociceptive DRG neurons.

The ligand-gated ion channel P2X7 receptor mediates NLRP3/caspase-1-mediated pyroptosis in cerebral cortical neurons of juvenile rats with sepsis.

Sepsis-associated encephalopathy (SAE) is a common complication of severe sepsis. Some studies have suggested that P2X7 receptors, a ligand-gated ion channel receptor subgroup activated by extracellular ATP, plays an important role in cell pyroptosis. However, the role of P2X7 receptors in the development of SAE with pyroptosis and its pathways are still unclear. In this study, we established a juvenile rat model of sepsis by cecal ligation and perforation, and showed that there was a significant increase in P2X7 receptor expression in the cortex of juvenile rats with sepsis. When the P2X7 receptor antagonist was administrated, the pyroptosis and extracellular-signal-regulated kinase (ERK) 1/2 signaling pathway were inhibited, and when the P2X7 receptor agonist was administrated, the pyroptosis and ERK1/2 signaling pathway were further activated. In addition, we also found that the administration of ERK1/2 signaling pathway inhibitor not only weakened downstream pyroptosis, but also caused the inhibition of upstream P2X7 receptor expression. In conclusion, our findings illustrated that the ligand-gated ion channel P2X7 receptor mediates NLRP3/caspase-1-related pyroptosis in cerebral cortex of juvenile rats with sepsis through ERK1/2 signaling pathway and plays a neuroprotective role.

ATP and ADP enhance DNA damage repair in γ-irradiated BEAS-2B human bronchial epithelial cells through activation of P2X7 and P2Y12 receptors.

Agents that promote DNA repair may be useful as radioprotectants to minimize side effects such as radiation pneumonia caused by damage to normal cells during radiation therapy to treat lung cancer. We have reported that extracellular nucleotides and nucleosides are involved in the P2 or P1 receptor-mediated DNA damage response (DDR) after γ-irradiation. Here, we investigated the effects of ATP, UTP, GTP, ITP and their metabolites on the γH2AX/53BP1 focus formation in nuclei (a measure of γ-irradiation-induced DDR) and the survival of γ-irradiated immortalized human bronchial epithelial (BEAS-2B) cells. Fluorescence immunostaining showed that ATP and ADP increase DDR and DNA repair, and exhibit radioprotective effects as evaluated by colony formation assay. These effects of ATP or ADP were blocked by inhibitors of P2X7 or P2Y12 receptor, respectively, and by ERK1/2 inhibitor. ATP and ADP enhanced phosphorylation of ERK1/2 by suppressing MKP-1 and MKP-3 expression after γ-irradiation. These results indicate that ATP and ADP exhibit radioprotective effects by phosphorylation of ERK1/2 via activation of P2X7 and P2Y12 receptors, respectively, to promote γ-irradiation-induced DDR and DNA repair. ATP and ADP appear to be candidates for radioprotectants to reduce damage to non-cancerous cells during lung cancer radiotherapy by promoting DDR and DNA repair.

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.

Lithocholic acid inhibits P2X2 and potentiates P2X4 receptor channel gating.

The family of ATP-gated purinergic P2X receptors comprises seven bunits (P2X1-7) that are unevenly distributed in the central and peripheral nervous systems as well as other organs. Endogenous modulators of P2X receptors are phospholipids, steroids and neurosteroids. Here, we analyzed whether bile acids, which are natural products derived from cholesterol, affect P2X receptor activity. We examined the effects of primary and secondary bile acids and newly synthesized derivatives of lithocholic acid on agonist-induced responses in HEK293T cells expressing rat P2X2, P2X4 and P2X7 receptors. Electrophysiology revealed that low micromolar concentrations of lithocholic acid and its structural analog 4-dafachronic acid strongly inhibit ATP-stimulated P2X2 but potentiate P2X4 responses, whereas primary bile acids and other secondary bile acids exhibit no or reduced effects only at higher concentrations. Agonist-stimulated P2X7 responses are significantly potentiated by lithocholic acid at moderate concentrations. Structural modifications of lithocholic acid at positions C-3, C-5 or C-17 abolish both inhibitory and potentiation effects to varying degrees, and the 3α-hydroxy group contributes to the ability of the molecule to switch between potentiation and inhibition. Lithocholic acid allosterically modulates P2X2 and P2X4 receptor sensitivity to ATP, reduces the rate of P2X4 receptor desensitization and antagonizes the effect of ivermectin on P2X4 receptor deactivation. Alanine-scanning mutagenesis of the upper halve of P2X4 transmembrane domain-1 revealed that residues Phe48, Val43 and Tyr42 are important for potentiating effect of lithocholic acid, indicating that modulatory sites for lithocholic acid and ivermectin partly overlap. Lithocholic acid also inhibits ATP-evoked currents in pituitary gonadotrophs expressing native P2X2, and potentiates ATP currents in nonidentified pituitary cells expressing P2X4 receptors. These results indicate that lithocholic acid is a bioactive steroid that may help to further unveil the importance of the P2X2, and P2X4 receptors in many physiological processes.

Resolving the Ionotropic P2X4 Receptor Mystery Points Towards a New Therapeutic Target for Cardiovascular Diseases.

Adenosine triphosphate (ATP) is a primordial versatile autacoid that changes its role from an intracellular energy saver to a signaling molecule once released to the extracellular milieu. Extracellular ATP and its adenosine metabolite are the main activators of the P2 and P1 purinoceptor families, respectively. Mounting evidence suggests that the ionotropic P2X4 receptor (P2X4R) plays pivotal roles in the regulation of the cardiovascular system, yet further therapeutic advances have been hampered by the lack of selective P2X4R agonists. In this review, we provide the state of the art of the P2X4R activity in the cardiovascular system. We also discuss the role of P2X4R activation in kidney and lungs vis a vis their interplay to control cardiovascular functions and dysfunctions, including putative adverse effects emerging from P2X4R activation. Gathering this information may prompt further development of selective P2X4R agonists and its translation to the clinical practice.

Inhibitory Effect of Cannabidiol on the Activation of NLRP3 Inflammasome Is Associated with Its Modulation of the P2X7 Receptor in Human Monocytes.

Cannabidiol (CBD), a phytocannabinoid, has been reported to have anti-inflammatory effects associated with NLRP3 inflammasome activation, but its mechanism of anti-inflammasome action remains unclear. Herein, we report CBD's effect on NLRP3 inflammasome activation and its modulation of P2X7, an inflammasome activation-related receptor, in human THP-1 monocytes. CBD (0.1, 1, and 10 µM) exerted anti-inflammasome activity in LPS-nigericin-stimulated THP-1 monocytes by reducing media IL-1ß concentration (by 63.9%, 64.1%, and 83.1%, respectively), which was similar to the known NLRP3 inflammasome inhibitors oridonin and MCC950 (16.9% vs 20.8% and 17.4%, respectively; at 10 µM). CBD (10 µM) decreased nigericin-alone- and nigericin-lipopolysaccharide-induced potassium efflux by 13.7% and 13.0%, respectively, in THP-1 monocytes, strongly suggesting P2X7 receptor modulation. Computational docking data supported the potential for CBD binding to the P2X7 receptor via interaction with GLU 172 and VAL 173 residues. Overall, the observed CBD suppressive effect on NLRP3 inflammasome activation in THP-1 monocytes was associated with decreased potassium efflux, as well as in silico prediction of P2X7 receptor binding. CBD inhibitory effects on the NLRP3 inflammasome may contribute to the overall anti-inflammatory effects reported for this phytocannabinoid.

The role of P2X4 receptor in neuropathic pain and its pharmacological properties.

Neuropathic pain (NPP) is a common symptom of most diseases in clinic, which seriously affects the mental health of patients and brings certain pain to patients. Due to its pathological mechanism is very complicated, and thus, its treatment has been one of the challenges in the field of medicine. Therefore, exploring the pathogenesis and treatment approach of NPP has aroused the interest of many researchers. ATP is an important energy information substance, which participates in the signal transmission in the body. The P2 × 4 receptor (P2 × 4R) is dependent on ATP ligand-gated cationic channel receptor, which can be activated by ATP and plays an important role in the transmission of information in the nervous system and the formation of pain. In this paper, we provide a comprehensive review of the structure and function of the P2 × 4R gene. We also discuss the pathogenesis of NPP and the intrinsic relationship between P2 × 4R and NPP. Moreover, we explore the pharmacological properties of P2 × 4R antagonists or inhibitors used as targeted therapies for NPP.

Neurotensin induces hypothermia by activating both neuronal neurotensin receptor 1 and astrocytic neurotensin receptor 2 in the median preoptic nucleus.

Neurotensin (NTS) is a neuropeptide acting as a neuromodulator in the brain and is a very potent hypothermic agent. However, the cellular mechanisms of actions are not fully understood. Here we report that NTS increases the firing rate of preoptic GABAergic neurons by activating both neurotensin receptor 1 (NTSR1) and neurotensin receptor 2 (NTSR2), expressed by neurons and astrocytes, respectively. Downstream of NTSR1 the neuropeptide activated an inward current, calcium release from intracellular stores and, postsynaptically, increased frequency and amplitude of inhibitory synaptic events. NTSR2 activation in astrocytes resulted in increased excitatory input in preoptic GABAergic neurons, an effect which was dependent upon the activation of P2X4 receptors. We also found that neuromedin N acted as a selective agonist at the NTSR1. Surprisingly, activation of both NTSR1 and NTSR2 in the median preoptic nucleus was required for activating a full hypothermic response.

Adenosine-5'-triphosphate suppresses proliferation and migration capacity of human endometrial stem cells.

Extracellular ATP through the activation of the P2X and P2Y purinergic receptors affects the migration, proliferation and differentiation of many types of cells, including stem cells. High plasticity, low immunogenicity and immunomodulation ability of mesenchymal stem cells derived from human endometrium (eMSCs) allow them to be considered a prominent tool for regenerative medicine. Here, we examined the role of ATP in the proliferation and migration of human eMSCs. Using a wound healing assay, we showed that ATP-induced activation of purinergic receptors suppressed the migration ability of eMSCs. We found the expression of one of the ATP receptors, the P2X7 receptor in eMSCs. In spite of this, cell activation with specific P2X7 receptor agonist, BzATP did not significantly affect the cell migration. The allosteric P2X7 receptor inhibitor, AZ10606120 also did not prevent ATP-induced inhibition of cell migration, confirming that inhibition occurs without P2X7 receptor involvement. Flow cytometry analysis showed that high concentrations of ATP did not have a cytotoxic effect on eMSCs. At the same time, ATP induced the cell cycle arrest, suppressed the proliferative and migration capacity of eMSCs and therefore could affect the regenerative potential of these cells.

P2X7 receptor activity landscape in rat and human glioma cell lines.

P2X7 is a commonly expressed purinergic receptor, which functions as a cation-permeable channel in the plasma membrane. In certain circumstances, the receptor may also form a large transmembrane pore what results in cell death. P2X7 receptors control numerous physiological and pathological cellular processes and their overexpression is often associated with cancer progression. As nucleotides are important signaling molecules in the central nervous system, P2X7 plays also an important but ambiguous role in glioma biology with contrary observations originating from different glioma models. Therefore, the aim of our research was to investigate P2X7 receptor expression and functions in three human (U-87 MG, U-138 MG, U-251 MG) and one rat (C6) glioma cell lines. Although the receptor mRNA and protein were present in all the studied cells, we found profound differences in their level. We also encountered a problem with one human cell lines authenticity (U-87 MG) and excluded it from most of the experiments. Interestingly, there was no clear dependency between P2X7 receptor level, calcium signal and pore formation ability in the studied glioma lines. In U-138 human cell line, the receptor seemed to be inactive, while in U-251 human and C6 rat cell line its activation resulted in calcium influx and large pore formation. However, the viability of studied cells upon the administration of specific P2X7 agonist - BzATP - was not affected for U-138 and U-251, whereas for C6 cells a stimulatory effect was observed. Our results stress the variability of P2X7 signaling in glioma models and the need for future research which would take into account the complicated landscape of the receptor signaling in the brain.

Prevention and rescue of cardiac dysfunction by methanocarba adenosine monophosphonate derivatives.

Accumulating evidence supports a therapeutic role of purinergic signaling in cardiac diseases. Previously, efficacy of systemically infused MRS2339, a charged methanocarba derivative of 2-Cl-adenosine monophosphate, was demonstrated in animal models of heart failure. We now test the hypothesis that an uncharged adenine nucleoside phosphonate, suitable as an oral agent with a hydrolysis-resistant phospho moiety, can prevent the development of cardiac dysfunction in a post-infarction ischemic or pressure overload-induced heart failure model in mice. The diester-masked uncharged phosphonate MRS2978 was efficacious in preventing cardiac dysfunction with improved left ventricular (LV) fractional shortening when administered orally at the onset of ischemic or pressure overload-induced heart failure. MRS2925, the charged, unmasked MRS2978 analog, prevented heart dysfunction when infused subcutaneously but not by oral gavage. When administered orally or systemically, MRS2978 but not MRS2925 could also rescue established cardiac dysfunction in both ischemic and pressure overload heart failure models. The diester-masked phosphate MRS4074 was highly efficacious at preventing the development of dysfunction as well as in rescuing pressure overload-induced and ischemic heart failure. MRS2978 was orally bioavailable (57-75%) giving rise to MRS2925 as a minor metabolite in vivo, tested in rats. The data are consistent with a novel therapeutic role of adenine nucleoside phosphonates in systolic heart failure.

Curcumin amends Ca2+ dysregulation in microglia by suppressing the activation of P2X7 receptor.

Curcumin (Cur) is widely used as an anti-inflammation agent and has anti-depression potential. Neuroinflammation mediated by Ca2+ channel activation is closely associated with the progression of post-stroke depression (PSD). In the current study, the role of P2X7 receptor (P2X7R) in the anti-PSD function of Cur was explored. Rats were subjected to middle cerebral artery occlusion (MCAO) surgery and chronic mild stress administration to induce PSD symptoms and then treated with Cur. The behaviors of rats were assessed with sucrose preference and forced swim tests. The accumulation of Ca2+ and the systemic inflammatory response in rats were detected. To determine the role of P2X7R in the anti-PSD function of curcumin, the PSD mice were further administrated with P2X7R agonist and antagonist. The administration of Cur attenuated behavior disorders associated with PSD. Moreover, the Ca2+ accumulation and the inflammatory response associated with PSD were also blocked by Cur. Cur also inhibited the activation of Ca2+ channel. The induced activity of P2X7R blocked the function of Cur by maintaining the symptoms of PSD in Cur-treated rats. Collectively, the anti-PSD function of Cur was dependent on the inhibition of P2X7R, which then deactivated Ca2+ channel-mediated inflammatory response associated with PSD progression.

P2RX2 and P2RX4 receptors mediate cation absorption in transitional cells and supporting cells of the utricular macula.

Purinergic receptors protect the cochlea during high-intensity stimulation by providing a parallel shunt pathway through non-sensory neighboring epithelial cells for cation absorption. So far, there is no direct functional evidence for the presence and type/subunit of purinergic receptors in the utricle of the vestibular labyrinth. The goal of the present study was to investigate which purinergic receptors are expressed and carry cation-absorption currents in the utricular transitional cells and macula. Purinergic agonists induced cation-absorption currents with a potency order of ATP > bzATP = αßmeATP â‰« ADP = UTP = UDP. ATP and bzATP are full agonists, whereas αßmeATP is a partial agonist. ATP-induced currents were partially inhibited by 100 µM suramin, 10 µM pyridoxal-phosphate-6-azo-(benzene-2,4-disulfonic acid (PPADS), or 5 µM 5-(3-bromophenyl)-1,3-dihydro-2H-benzofuro[3,2-e]-1, 4-diazepin-2-one (5-BDBD), and almost completely blocked by 100 µM Gd3+ or by a combination of 10 µM PPADS and 5 µM 5-BDBD. Expression of the P2RX2 and P2RX4 receptor was detected by immunocytochemistry in transitional cells and macular supporting cells. This is the first study to demonstrate that ATP induces cation currents carried by a combination of P2RX2 and P2RX4 in utricular transitional and macular epithelial cells, and supporting the hypothesis that purinergic receptors protect utricular hair cells during elevated stimulus intensity levels.

Role of Carbon Monoxide in the Mechanisms of Action of Extracellular ATP on Contractile Activity of Vascular Smooth Muscle Cells.

We studied the role of carbon monoxide (CO) in the effect of P2X and P2Y receptor agonist ATP on the tone of rat aorta segments with intact endothelium. ATP (1-1000 µM) and P2X receptor agonist α,ß-MeATP (100 µM) relaxed segments precontracted with phenylephrine (10 µM), while UTP (100-1000 µM) increased the amplitude of phenylephrine-induced contraction. The relaxing effect of ATP was enhanced by CORM II (100 µM), NO synthase inhibitor L-NAME, and guanylate cyclase inhibitor ODQ and attenuated by ZnPP IX (100 µM). The constrictive effect of UTP was weakened by CORM II (100 µM), but was not changed by ZnPP IX (100 µM). ZnPP IX (100 µM) weakened the relaxation response to α,ß-MeATP. Thus, ATP involves the CO-dependent signaling cascade through P2X receptors.