Alcohol action on membrane ion channels gated by extracellular ATP (P2X receptors)

Physicochemical Solubility of and Biological Sensitivity to Long-Chain Alcohols Determine the Cutoff Chain Length in Biological Activity

The cutoff phenomenon associated with the effectiveness of long-chain alcohols in the induction of anesthesia is also observed for various antimicrobial activities, although the mechanism has remained unknown for over eight decades. The minimum inhibitory concentrations at 25°C for budding yeast growth exponentially decreased with increasing chain length of n-alcohols (C2-C12), whereas alcohols ≥C13 lost the inhibitory effect. Thus, growth inhibition by n-alcohols obeys the Meyer-Overton correlation up to C12 and exhibits a cutoff phenomenon. The densities of n-alcohols are low, and the melting point and hydrophobicity increase with chain length. C13 and C14 inhibited yeast growth at 39.8°C, above their melting points. Alcohols ≤C14 inhibited thermophilic bacterial growth at 50°C, whereas C16 inhibited it at 67.5°C, above their melting points. Thus, the high melting points of long-chain alcohols contribute to the cutoff phenomenon. C14 did not effectively inhibit yeast growth in a static culture at 39.8°C, in contrast to a shaking culture, in which the low density-dependent concentration gradient was eliminated. The duration of the transient growth inhibition of yeast by C12 was prolonged by sonication, which prevented hydrophobic aggregation. Therefore, a nonuniform distribution owing to low density and high hydrophobicity contributes to the cutoff. C14 inhibited the growth at 25°C of the pdr1,3,5 mutant, defective in multidrug efflux pumps, whereas C12 did not inhibit the growth of yeast overexpressing PDR5, indicating that the sensitivity to long-chain alcohols contributed to the cutoff. A balance between the physicochemical solubility of and the biological sensitivity to long-chain alcohols determines the cutoff chain length.

Japanese Rice Wine can reduce psychophysical stress-induced depression-like behaviors and Fos expression in the trigeminal subnucleus caudalis evoked by masseter muscle injury in the rats

We determined if Japanese Rice Wine (Sake) had inhibitory effects on stress-induced enhancement of masseter muscle (MM) nociception in the rats. Male rats were subjected to the repeated forced swim stress (FS) or sham conditionings from Day -3 to -1. Daily administration of Sake or saline was conducted after each stress conditioning. At Day 0 the number of Fos positive cells, a marker for neural activity, was quantified at the trigeminal subnucleus caudalis (Vc) region by MM injury with formalin. FS increased MM-evoked Fos expression in the Vc region, which was inhibited by Sake compared to saline administration. Sake did not alter the number of Fos positive cells under sham conditions, indicating that inhibitory roles of Sake on neural activity in the Vc region were seen under FS conditions. These findings indicated that Sake had inhibitory roles on stress-induced MM nociception at the Vc region in our experimental conditions.

Fluorinated Alcohols' Effects on Lipid Bilayer Properties

Fluorinated alcohols (fluoroalcohols) have physicochemical properties that make them excellent solvents of peptides, proteins, and other compounds. Like other alcohols, fluoroalcohols also alter membrane protein function and lipid bilayer properties and stability. Thus, the questions arise: how potent are fluoroalcohols as lipid-bilayer-perturbing compounds, could small residual amounts that remain after adding compounds dissolved in fluoroalcohols alter lipid bilayer properties sufficiently to affect membranes and membrane protein function, and do they behave like other alcohols? To address these questions, we used a gramicidin-based fluorescence assay to determine the bilayer-modifying potency of selected fluoroalcohols: trifluoroethanol (TFE), HFIP, and perfluoro-tert-butanol (PFTB). These fluoroalcohols alter bilayer properties in the low (PFTB) to high (TFE) mM range. Using the same assay, we determined the bilayer partitioning of the alcohols. When referenced to the aqueous concentrations, the fluoroalcohols are more bilayer perturbing than their nonfluorinated counterparts, with the largest fluoroalcohol, PFTB, being the most potent and the smallest, TFE, the least. When referenced to the mole fractions in the membrane, however, the fluoroalcohols have equal or lesser bilayer-perturbing potency than their nonfluorinated counterparts, with TFE being more bilayer perturbing than PFTB. We compared the fluoroalcohols' molecular level bilayer interactions using atomistic molecular dynamics simulations and showed how, at higher concentrations, they can cause bilayer breakdown using absorbance measurements and ³¹P nuclear magnetic resonance.

Reduced expression of purinergic P2X4 receptors increases voluntary ethanol intake in C57BL/6J mice

Purinergic P2X4 receptors (P2X4Rs) belong to the P2X superfamily of ionotropic receptors that are gated by adenosine 5'-triphosphate (ATP). Accumulating evidence indicates that P2X4Rs play an important role in regulation of ethanol intake. At the molecular level, ethanol's inhibitory effects on P2X4Rs are antagonized by ivermectin (IVM), in part, via action on P2X4Rs. Behaviorally, male mice deficient in the p2rx4 gene (P2X4R knockout [KO]) have been shown to exhibit a transient increase in ethanol intake over a period of 4 days, as demonstrated by social and binge drinking paradigms. Furthermore, IVM reduced ethanol consumption in male and female rodents, whereas male P2X4R KO mice were less sensitive to the anti-alcohol effects of IVM, compared to wildtype (WT) mice, further supporting a role for P2X4Rs as targets of IVM's action. The current investigation extends testing the hypothesis that P2X4Rs play a role in regulation of ethanol intake. First, we tested the response of P2X4R KO mice to ethanol for a period of 5 weeks. Second, to gain insights into the changes in ethanol intake, we employed a lentivirus-shRNA (LV-shRNA) methodology to selectively knockdown P2X4R expression in the nucleus accumbens (NAc) core in male C57BL/6J mice. In agreement with our previous study, male P2X4R KO mice exhibited higher ethanol intake than WT mice. Additionally, reduced expression of P2X4Rs in the NAc core significantly increased ethanol intake and preference. Collectively, the findings support the hypothesis that P2X4Rs play a role in regulation of ethanol intake and that P2X4Rs represent a novel drug target for treatment of alcohol use disorder.

P2X4 receptors (P2X4Rs) represent a novel target for the development of drugs to prevent and/or treat alcohol use disorders

Alcohol use disorders (AUDs) have a staggering socioeconomic impact. Few therapeutic options are available, and they are largely inadequate. These shortcomings highlight the urgent need to develop effective medications to prevent and/or treat AUDs. A critical barrier is the lack of information regarding the molecular target(s) by which ethanol (EtOH) exerts its pharmacological activity. This review highlights findings implicating P2X4 receptors (P2X4Rs) as a target for the development of therapeutics to treat AUDs and discusses the use of ivermectin (IVM) as a potential clinical tool for treatment of AUDs. P2XRs are a family of ligand-gated ion channels (LGICs) activated by extracellular ATP. Of the P2XR subtypes, P2X4Rs are expressed the most abundantly in the CNS. Converging evidence suggests that P2X4Rs are involved in the development and progression of AUDs. First, in vitro studies report that pharmacologically relevant EtOH concentrations can negatively modulate ATP-activated currents. Second, P2X4Rs in the mesocorticolimbic dopamine system are thought to play a role in synaptic plasticity and are located ideally to modulate brain reward systems. Third, alcohol-preferring (P) rats have lower functional expression of the p2rx4 gene than alcohol-non-preferring (NP) rats suggesting an inverse relationship between alcohol intake and P2X4R expression. Similarly, whole brain p2rx4 expression has been shown to relate inversely to innate 24 h alcohol preference across 28 strains of rats. Fourth, mice lacking the p2rx4 gene drink more EtOH than wildtype controls. Fifth, IVM, a positive modulator of P2X4Rs, antagonizes EtOH-mediated inhibition of P2X4Rs in vitro and reduces EtOH intake and preference in vivo. These findings suggest that P2X4Rs contribute to EtOH intake. The present review summarizes recent findings focusing on the P2X4R as a molecular target of EtOH action, its role in EtOH drinking behavior and modulation of its activity by IVM as a potential therapy for AUDs.

Contribution of P2X4 receptors to ethanol intake in male C57BL/6 mice

P2X receptors (P2XRs) are a family of cation-permeable ligand-gated ion channels activated by synaptically released extracellular adenosine 5'-triphosphate. The P2X4 subtype is abundantly expressed in the central nervous system and is sensitive to low intoxicating ethanol concentrations. Genetic meta-analyses identified the p2rx4 gene as a candidate gene for innate alcohol intake and/or preference. The current study used mice lacking the p2rx4 gene (knockout, KO) and wildtype (WT) C57BL/6 controls to test the hypothesis that P2X4Rs contribute to ethanol intake. The early acquisition and early maintenance phases of ethanol intake were measured with three different drinking procedures. Further, we tested the effects of ivermectin (IVM), a drug previously shown to reduce ethanol's effects on P2X4Rs and to reduce ethanol intake and preference, for its ability to differentially alter stable ethanol intake in KO and WT mice. Depending on the procedure and the concentration of the ethanol solution, ethanol intake was transiently increased in P2X4R KO versus WT mice during the acquisition of 24-h and limited access ethanol intake. IVM significantly reduced ethanol intake in P2X4R KO and WT mice, but the degree of reduction was 50 % less in the P2X4R KO mice. Western blot analysis identified significant changes in γ-aminobutyric acidA receptor α1 subunit expression in brain regions associated with the regulation of ethanol behaviors in P2X4R KO mice. These findings add to evidence that P2X4Rs contribute to ethanol intake and indicate that there is a complex interaction between P2X4Rs, ethanol, and other neurotransmitter receptor systems.

Activation and regulation of purinergic P2X receptor channels

Mammalian ATP-gated nonselective cation channels (P2XRs) can be composed of seven possible subunits, denoted P2X1 to P2X7. Each subunit contains a large ectodomain, two transmembrane domains, and intracellular N and C termini. Functional P2XRs are organized as homomeric and heteromeric trimers. This review focuses on the binding sites involved in the activation (orthosteric) and regulation (allosteric) of P2XRs. The ectodomains contain three ATP binding sites, presumably located between neighboring subunits and formed by highly conserved residues. The detection and coordination of three ATP phosphate residues by positively charged amino acids are likely to play a dominant role in determining agonist potency, whereas an AsnPheArg motif may contribute to binding by coordinating the adenine ring. Nonconserved ectodomain histidines provide the binding sites for trace metals, divalent cations, and protons. The transmembrane domains account not only for the formation of the channel pore but also for the binding of ivermectin (a specific P2X4R allosteric regulator) and alcohols. The N- and C- domains provide the structures that determine the kinetics of receptor desensitization and/or pore dilation and are critical for the regulation of receptor functions by intracellular messengers, kinases, reactive oxygen species and mercury. The recent publication of the crystal structure of the zebrafish P2X4.1R in a closed state provides a major advance in the understanding of this family of receptor channels. We will discuss data obtained from numerous site-directed mutagenesis experiments accumulated during the last 15 years with reference to the crystal structure, allowing a structural interpretation of the molecular basis of orthosteric and allosteric ligand actions.

Ethanol is a fast channel inhibitor of P2X4 receptors

P2X receptors (P2XRs) are ion channels gated by synaptically released ATP. The P2X4 is the most abundant P2XR subtype expressed in the central nervous system and to date is the most ethanol-sensitive. In addition, genomic findings suggest that P2X4Rs may play a role in alcohol intake/preference. However, little is known regarding how ethanol causes the inhibition of ATP-gated currents in P2X4Rs. We begin to address this issue by investigating the effects of ethanol in wild-type and mutant D331A and M336A P2X4Rs expressed in human embryonic kidney (HEK) 293 cells using whole-cell patch-clamp methods. The results suggest that residues D331 and M336 play a role in P2X4R gating and ethanol inhibits channel functioning via a mechanism different from that in other P2XRs. Key findings from the study include: 1) ethanol inhibits ATP-gated currents in a rapid manner; 2) ethanol inhibition of ATP-gated currents does not depend on voltage and ATP concentration; 3) residues 331 and 336 slow P2X4 current deactivation and regulate the inhibitory effects of ethanol; and 4) ethanol effects are similar in HEK293 cells transfected with P2X4Rs and cultured rat hippocampal neurons transduced with P2X4Rs using a recombinant lentiviral system. Overall, these findings provide key information regarding the mechanism of ethanol action on ATP-gated currents in P2X4Rs and provide new insights into the biophysical properties of P2X4Rs.

Pharmacologically targeting the P2rx4 gene on maintenance and reinstatement of alcohol self-administration in rats

Genetic studies indicate that alcohol consumption associates with expression of the P2rx4 gene, a gene that codes for the P2X(4) receptor. This receptor is a subtype in the purinergic system of ligand-gated ion channels that when activated exerts excitatory effects in CNS. P2X(4) function is inhibited by alcohol and P2X(4) receptors are modulated positively by the antiparasitic agent, ivermectin. Two experiments were performed to test the ability of ivermectin to alter the behavioral effects of alcohol in rats. After alcohol exposure was achieved via the "drinking in the dark" procedure, separate groups of Sprague-Dawley rats were trained to lever press for either alcohol (10% ethanol/2% sucrose) or sucrose (3%) solutions in operant chambers. Rats were tested for maintenance of operant self-administration under a progressive ratio condition (Experiment 1) and for reinstatement of extinguished responding induced by solution presentation (Experiment 2) after ivermectin (0; 1-10mg/kg; IP) administration. Ivermectin decreased the amount of work that the animal performed to obtain reinforcers in the maintenance study, particularly in the group reinforced with alcohol, and tended to decrease reinstated lever press responding. Conditioned approach behavior (head entries) was significantly reduced by ivermectin in both experiments. Reduction in motor activity was seen during the longer maintenance sessions but not in the shorter reinstatement sessions. Results suggest some support for ivermectin-like drugs as potential treatment agents for alcohol dependence. Caution is warranted due to modest specificity on behavior reinforced by alcohol, some reduction in general activity levels, and the lack of dose-response effects.

Molecular targets and mechanisms for ethanol action in glycine receptors

Glycine receptors (GlyRs) are recognized as the primary mediators of neuronal inhibition in the spinal cord, brain stem and higher brain regions known to be sensitive to ethanol. Building evidence supports the notion that ethanol acting on GlyRs causes at least a subset of its behavioral effects and may be involved in modulating ethanol intake. For over two decades, GlyRs have been studied at the molecular level as targets for ethanol action. Despite the advances in understanding the effects of ethanol in vivo and in vitro, the precise molecular sites and mechanisms of action for ethanol in ligand-gated ion channels in general, and in GlyRs specifically, are just now starting to become understood. The present review focuses on advances in our knowledge produced by using molecular biology, pressure antagonism, electrophysiology and molecular modeling strategies over the last two decades to probe, identify and model the initial molecular sites and mechanisms of ethanol action in GlyRs. The molecular targets on the GlyR are covered on a global perspective, which includes the intracellular, transmembrane and extracellular domains. The latter has received increasing attention in recent years. Recent molecular models of the sites of ethanol action in GlyRs and their implications to our understanding of possible mechanism of ethanol action and novel targets for drug development in GlyRs are discussed.

Loop 2 structure in glycine and GABA(A) receptors plays a key role in determining ethanol sensitivity

The present study tests the hypothesis that the structure of extracellular domain Loop 2 can markedly affect ethanol sensitivity in glycine receptors (GlyRs) and gamma-aminobutyric acid type A receptors (GABA(A)Rs). To test this, we mutated Loop 2 in the alpha1 subunit of GlyRs and in the gamma subunit of alpha1beta2gamma2GABA(A)Rs and measured the sensitivity of wild type and mutant receptors expressed in Xenopus oocytes to agonist, ethanol, and other agents using two-electrode voltage clamp. Replacing Loop 2 of alpha1GlyR subunits with Loop 2 from the deltaGABA(A)R (deltaL2), but not the gammaGABA(A)R subunit, reduced ethanol threshold and increased the degree of ethanol potentiation without altering general receptor function. Similarly, replacing Loop 2 of the gamma subunit of GABA(A)Rs with deltaL2 shifted the ethanol threshold from 50 mm in WT to 1 mm in the GABA(A) gamma-deltaL2 mutant. These findings indicate that the structure of Loop 2 can profoundly affect ethanol sensitivity in GlyRs and GABA(A)Rs. The deltaL2 mutations did not affect GlyR or GABA(A)R sensitivity, respectively, to Zn(2+) or diazepam, which suggests that these deltaL2-induced changes in ethanol sensitivity do not extend to all allosteric modulators and may be specific for ethanol or ethanol-like agents. To explore molecular mechanisms underlying these results, we threaded the WT and deltaL2 GlyR sequences onto the x-ray structure of the bacterial Gloeobacter violaceus pentameric ligand-gated ion channel homologue (GLIC). In addition to being the first GlyR model threaded on GLIC, the juxtaposition of the two structures led to a possible mechanistic explanation for the effects of ethanol on GlyR-based on changes in Loop 2 structure.

Acute alcohol action and desensitization of ligand-gated ion channels

Ethanol exerts its biological actions through multiple receptors, including ion channels. Ion channels that are sensitive to pharmacologically relevant ethanol concentrations constitute a heterogeneous set, including structurally unrelated proteins solely sharing the property that their gating is regulated by a ligand(s). Receptor desensitization is almost universal among these channels, and its modulation by ethanol may be a crucial aspect of alcohol pharmacology and effects in the body. We review the evidence documenting interactions between ethanol and ionotropic receptor desensitization, and the contribution of this interaction to overall ethanol action on channel function. In some cases, such as type 3 serotonin, nicotinic acetylcholine, GABA-A, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors, ethanol actions on apparent desensitization play a significant role in acute drug action on receptor function. In a few cases, mutagenesis helped to identify different areas within a receptor protein that differentially sense n-alcohols, resulting in differential modulation of receptor desensitization. However, desensitization of a receptor is linked to a variety of biochemical processes that may alter protein conformation, such as the lipid microenvironment, post-translational channel modification, and channel subunit composition, the relative contribution of these processes to ethanol interactions with channel desensitization remains unclear. Understanding interactions between ethanol and ionotropic receptor desensitization may help to explain different ethanol actions 1) when ethanol is evaluated in vitro on cloned channel proteins, 2) under physiological or pathological conditions or in distinct cell domains with modified ligand concentration and/or receptor conformation. Finally, receptor desensitization is likely to participate in molecular and, possibly, behavioral tolerance to ethanol, which is thought to contribute to the risk of alcoholism.

Roles of ectodomain and transmembrane regions in ethanol and agonist action in purinergic P2X2 and P2X3 receptors

The present work investigated sites of ethanol action in ATP-gated P2X receptors (P2XRs) using chimeric strategies that exploited the differences in ethanol response between P2X2R (inhibition) and P2X3R (potentiation). We tested ethanol (10-200mM) effects on ATP- and alpha,beta-methylene-ATP (alpha,beta-meATP)-induced currents in wildtype P2X2, P2X3 and chimeric P2X2/P2X3Rs expressed in Xenopus oocytes using two-electrode voltage-clamp (-70mV). Exchanging ectodomain regions of P2X2 and P2X3Rs reversed wildtype ethanol responses. Substituting back portions of the P2X2R ectodomain at TM interfaces in chimeras that contained the P2X3R ectodomain restored wildtype P2X2R-like ethanol response. Point mutations that replaced non-conserved ectodomain residues at TM interfaces of P2X3Rs with homologous P2X2R residues identified positions that reversed the direction (304) or changed the magnitude (53, 55 and 313) of ethanol response. Homologous substitutions in P2X2Rs did not significantly alter wildtype P2X2R-like ethanol responses. These findings suggest that ectodomain segments at TM interfaces play key roles in determining qualitative and quantitative responses to ethanol of P2X2 and P2X3Rs. Studies that substituted TM regions of P2X3R with respective P2X2R TMs indicate that the TM1, but not the TM2, region plays a role in determining the magnitude of ethanol response. Studies with ATP and alpha,beta-meATP support prior indications that TM regions are important in agonist desensitization and suggest that both ectodomain and TM regions play roles in determining agonist potency and selectivity. Overall, these findings are the first to identify potential targets for ethanol in P2X2 and P2X3Rs and should provide insight into the sites of ethanol action in other P2XRs.

Effect of chronic administration of ethanol on the regulation of the delta-subunit of GABA(A) receptors in the rat brain

In the present study, we investigated the effect of chronic ethanol (CE) administration on the polypeptide levels of the delta-subunit of GABA(A) receptors and [(3)H]muscimol binding to the immunoprecipitated delta-subunit-containing GABA(A) receptor assemblies in the rat brain. CE administration resulted a down-regulation of polypeptide levels of the delta-subunit of GABA(A) receptors in the rat cerebellum and hippocampus, whereas there were no changes in the delta-subunit polypeptide levels in the rat cerebral cortex. Further, CE administration caused a down-regulation of native delta-subunit-containing GABA(A) receptor assemblies in the rat cerebellum as determined by [(3)H]muscimol binding to the immunoprecipitated receptor assemblies. These results indicate that the delta-subunit-containing GABA(A) receptors may play a role in chronic ethanol-induced tolerance and dependence.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Effects of ethanol on tonic GABA currents in cerebellar granule cells and mammalian cells recombinantly expressing GABA(A) receptors

The effects of ethanol on the GABA(A) receptors, which are regarded as one of the most important target sites of ethanol, are very controversial, ranging from potentiation to no effect. The delta subunit-containing GABA(A) receptors expressed in Xenopus oocytes were recently reported to be potently augmented by ethanol. We performed patch-clamp experiments using the cerebellar granule cells and mammalian cells expressing recombinant GABA(A) receptors. In granule cells, the sensitivity to GABA increased from 7 to 11 days in vitro. Furosemide, an antagonist of alpha6-containing GABA(A) receptors, inhibited GABA-induced currents more potently at 11 to 14 days than at 7 days. Ethanol at 30 mM had either no effect or an inhibitory effect on currents induced by low concentrations of GABA in granule cells. On alpha4beta2delta, alpha6beta2delta, or alpha6beta3deltaGABA(A) receptors expressed in Chinese hamster ovary cells, ethanol at 10, 30, and 100 mM had either no effect or an inhibitory effect on GABA currents. Ethanol inhibition of GABA(A) receptor was observed in all of the subunit combinations examined. In contrast, the perforated patch-clamp method to record the GABA currents revealed ethanol effects on the alpha6beta2delta subunits ranging from slight potentiation to slight inhibition. Ethanol seems to exert a dual action on the GABA(A) receptors and the potentiating action may depend on intracellular milieu. Thus, the differences between the GABA(A) receptors expressed in mammalian host cells and those in Xenopus oocytes in the response to ethanol might be due to changes in intracellular components under patch-clamp conditions.

cis-Regulatory sequences of the genes involved in apoptosis, cell growth, and proliferation may provide a target for some of the effects of acute ethanol exposure

The physiological effects of alcohol are known to include drunkenness, toxicity, and addiction leading to alcohol-related health and societal problems. Some of these effects are mediated by regulation of expression of many genes involved in alcohol response pathways. Analysis of the regulatory elements and biological interaction of the genes that show coexpression in response to alcohol may give an insight into how they are regulated. Fifty-two ethanol-responsive (ER) genes displaying differential expression in mouse brain in response to acute ethanol exposure were subjected to bioinformatics analysis to identify known or putative transcription factor binding sites and cis-regulatory modules in the promoter regions that may be involved in their responsiveness to alcohol. Functional interactions of these genes were also examined to assess their cumulative contribution to metabolomic pathways. Clustering and promoter sequence analysis of the ER genes revealed the DNA binding site for nuclear transcription factor Y (NFY) as the most significant. NFY also take part in the proposed biological association network of a number of ER genes, where these genes interact with themselves and other cellular components, and may generate a major cumulative effect on apoptosis, cell survival, and proliferation in response to alcohol. NFY has the potential to play a critical role in mediating the expression of a set of ER genes whose interactions contribute to apoptosis, cell survival, and proliferation, which in turn may affect alcohol-related behaviors.

P2 receptors and neuronal injury

Extracellular adenosine 5'-triphosphate (ATP) was proposed to be an activity-dependent signaling molecule that regulates glia-glia and glia-neuron communications. ATP is a neurotransmitter of its own right and, in addition, a cotransmitter of other classical transmitters such as glutamate or GABA. The effects of ATP are mediated by two receptor families belonging either to the P2X (ligand-gated cationic channels) or P2Y (G protein-coupled receptors) types. P2X receptors are responsible for rapid synaptic responses, whereas P2Y receptors mediate slow synaptic responses and other types of purinergic signaling involved in neuronal damage/regeneration. ATP may act at pre- and postsynaptic sites and therefore, it may participate in the phenomena of long-term potentiation and long-term depression of excitatory synaptic transmission. The release of ATP into the extracellular space, e.g., by exocytosis, membrane transporters, and connexin hemichannels, is a widespread physiological process. However, ATP may also leave cells through their plasma membrane damaged by inflammation, ischemia, and mechanical injury. Functional responses to the activation of multiple P2 receptors were found in neurons and glial cells under normal and pathophysiological conditions. P2 receptor-activation could either be a cause or a consequence of neuronal cell death/glial activation and may be related to detrimental and/or beneficial effects. The present review aims at demonstrating that purinergic mechanisms correlate with the etiopathology of brain insults, especially because of the massive extracellular release of ATP, adenosine, and other neurotransmitters after brain injury. We will focus in this review on the most important P2 receptor-mediated neurodegenerative and neuroprotective processes and their beneficial modulation by possible therapeutic manipulations.

Keynote review: Allosterism in membrane receptors

Allosteric modulation of membrane receptors has been intensively studied in the past three decades and is now considered to be an important indirect mechanism for the control of receptor function. The allosteric site on the GABA(A) receptor is the target for the most widely prescribed sleep medicines, the benzodiazepines. Cinacalcet, an allosteric enhancer of the calcium-sensing receptor, is used to treat secondary hyperparathyroidism. Allosteric ligands might be especially valuable to control receptors for which the design of selective orthosteric agonists or antagonists has been elusive, such as muscarinic acetylcholine receptors.

The mechanism by which ethanol inhibits rat P2X4 receptors is altered by mutation of histidine 241

1. We investigated ethanol inhibition of the rat P2X(4) receptor and the contribution of the three histidine residues in the extracellular loop of this receptor to ethanol inhibition of receptor function, using site-directed mutagenesis and electrophysiological characterization of recombinant receptors. 2. In the wild-type receptor, 50, 200 and 500 mM ethanol increasingly shifted the ATP concentration-response curve to the right in a parallel manner, increasing the EC(50) value without affecting E(max). However, 750 or 900 mM ethanol did not produce a further increase in the EC(50) value of the ATP concentration-response curve, suggesting that this inhibition is not competitive. 3. The P2X(4) receptor mutations H140A and H286A did not significantly alter ethanol inhibition of ATP-activated current. By contrast, the mutation H241A changed the mechanism by which ethanol inhibits receptor function; viz., ethanol inhibition was not associated with an increased EC(50) value of the ATP concentration-response curve, instead, ethanol decreased the maximal response to ATP without affecting the EC(50) value of the ATP concentration-response curve. 4. Ethanol inhibition of the H241A mutant was voltage independent between -60 and +20 mV and ethanol did not alter the reversal potential of ATP-activated current. In addition, ethanol decreased the desensitization rate of the H241A-mediated current. 5. The purinoceptor antagonists, suramin and pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), did not alter the magnitude of ethanol inhibition of ATP-activated current in the H241A mutant. 6. The results suggest that ethanol inhibits the wild-type rat P2X(4) receptor by an allosteric action to increase the EC(50) value of the ATP concentration-response curve, the P2X(4) receptor mutation H241A alters the mechanism by which ethanol inhibits P2X(4) receptor function, and ethanol and PPADS or suramin appear to inhibit H241A-mutated receptors at independent sites.

Involvement of P2 receptors in the growth and survival of neurons in the CNS

Extracellular adenosine 5'-triphosphate (ATP) has been recognized as a ubiquitous, unstable signalling molecule, acting as a fast neurotransmitter and modulator of transmitter release and neuronal excitability. Recent findings have demonstrated that ATP is a growth factor participating in differentiation, cell proliferation, and survival, as well as a toxic agent that mediates cellular degeneration and death. Potential sources of extracellular purines in the nervous system include neurons, glia, endothelium, and blood. A complex family of ectoenzymes rapidly hydrolyzes or interconverts extracellular nucleotides, thereby either terminating their signalling action or producing an active metabolite of altered purinoceptor selectivity. Most effects are mediated through the 2 main subclasses of specific cell surface receptors, P2X and P2Y. Members of these P2X/Y receptor families are widely expressed in the central nervous system (CNS) and are involved in glia-glia and glia-neuron communications, whereby they play important physiological and pathophysiological roles in a variety of biological processes. After different kinds of "acute" CNS injury (e.g., ischemia, hypoxia, mechanical stress, axotomy), extracellular ATP can reach high concentrations, up to the millimolar range, flowing out from cells into the extracellular space, exocytotically, via transmembrane transport, or as a result of cell damage. In this review, P2 receptor activation as a cause or a consequence of neuronal cell activation or death and/or glial activation is described. The involvement of P2 receptors is also described under different "chronic" pathological conditions, such as pain, epilepsia, toxic influence of ethanol or amphetamine, retinal diseases, Alzheimer's disease (AD), and possibly, Parkinson's disease. The relationship between changes in P2 receptor expression and the specific response of different cell types to injury is extremely complex and can be related to detrimental and/or beneficial effects. The present review therefore considers ATP acting via P2 receptors as a potent regulator of normal physiological and pathological processes in the brain, with a focus on pathophysiological implications of P2 receptor functions.

Cut-off phenomenon in the protective effect of alcohols against lysophosphatidylcholine-induced calcium overload

We studied the effect of chain length on the protective effect of alcohols against lysophosphatidylcholine (LPC)-induced Ca2+ overload in neonatal rat cardiomyocytes. We previously found that ethanol retards Ca2+ elevation. Cells were loaded with the Ca2+-sensitive fluorophore fura-2, and changes in fluorescence were followed. The addition of 10 microM LPC increased Ca2+, which reached a plateau after an 8-10 min delay. The presence of 88 mM n-propanol, n-butanol, tert-butanol, or 2,2-dimethylpropanol significantly increased the delay by 94-213%. However, n-pentanol at 2 mM or 88 mM had no protective effect. Among n-alcohols, the increase in lag time was inversely proportional to the length of the carbon chain. Chain length, rather than molecular weight determines the effect, because 2,2-dimethylpropanol had a protective effect. The influence of alcohols on LPC micelle formation was estimated from the increase in octadecyl rhodamine B fluorescence; the increase by n-alcohols was directly proportional to chain length, indicating that micelle formation was not involved in the extension of lag time. The absence of the protective effect when the alcohol aliphatic chain exceeds four carbons suggests that the effect of ethanol may be mediated via a small lipophilic pocket on a protein, or to lateral pressure perturbation in the membrane.

General anesthetic octanol and related compounds activate wild-type and delF508 cystic fibrosis chloride channels

1. Cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel is defective during cystic fibrosis (CF). Activators of the CFTR Cl(-) channel may be useful for therapy of CF. Here, we demonstrate that a range of general anesthetics like normal-alkanols (n-alkanols) and related compounds can stimulate the Cl(-) channel activity of wild-type CFTR and delF508-CFTR mutant. 2. The effects of n-alkanols like octanol on CFTR activity were measured by iodide ((125)I) efflux and patch-clamp techniques on three distinct cellular models: (1). CFTR-expressing Chinese hamster ovary cells, (2). human airway Calu-3 epithelial cells and (3). human airway JME/CF15 epithelial cells which express the delF508-CFTR mutant. 3. Our data show for the first time that n-alkanols activate both wild-type CFTR and delF508-CFTR mutant. Octanol stimulated (125)I efflux in a dose-dependent manner in CFTR-expressing cells (wild-type and delF508) but not in cell lines lacking CFTR. (125)I efflux and Cl(-) currents induced by octanol were blocked by glibenclamide but insensitive to 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, as expected for a CFTR Cl(-) current. 4. CFTR activation by octanol was neither due to cell-to-cell uncoupling properties of octanol nor to an intracellular cAMP increase. CFTR activation by octanol requires phosphorylation by protein kinase-A (PKA) since it was prevented by H-89, a PKA inhibitor. 5. n-Alkanols chain length was an important determinant for channel activation, with rank order of potencies: 1-heptanol<1-octanol<2-octanol<1-decanol. Our findings may be of valuable interest for developing novel therapeutic strategies for CF.

Effects of ethanol on deep pain evoked by formalin injected in TMJ of rat

It has been reported that ethanol can alter nociceptive sensitivity from superficial tissues, such as skin and subcutaneous region. However, the influence of ethanol on deep pain conditions is not understood. The aim of this study was to demonstrate the acute, chronic and ethanol withdrawal effects on nociceptive behavioral responses induced by the injection of formalin into the temporomandibular joint (TMJ) region of rats. In experiment 1, rats were injected with ethanol (2,5 g/Kg, i.p.) or an equal volume of saline 15 min before the administration of formalin (1.5%) into the TMJ. Rats pretreated with ethanol showed a decrease in nociceptive behavioral responses. In experiment 2, rats were given an ethanol solution (6.5%) or tap water to drink for 4 and 10 days. On day 4, the animals (ethanol group) showed amounts of analgesia when submitted to the TMJ formalin test. Tolerance to the antinociceptive effects was observed on day 10. Behavioral hyperalgesia was verified 12 hr after withdrawal in another group that drank ethanol for 10 days. These results show that ethanol can affect the nociceptive responses related to deep pain evoked by the TMJ formalin test.

Do we need zinc to think?

Chelatable Zn(2+), which is found in the synaptic vesicles of certain glutamatergic neurons in several regions of the forebrain, is released during neuronal activity. Zn(2+) exhibits numerous effects on ligand-gated and voltage-dependent ion channels, and released Zn(2+) is therefore likely able to modulate synaptic transmission. The physiologically relevant actions of Zn(2+), however, have remained unclear. Recent research exploiting improved Zn(2+)-sensitive optical probes has suggested some intriguing effects for synaptically released Zn(2+), including heterosynaptic regulation of N-methyl-D-aspartate (NMDA) receptor function, and a novel role as a trans-synaptic second messenger that may enter postsynaptic neurons to modulate various signal transduction pathways.

Characterization of P2X3, P2Y1 and P2Y4 receptors in cultured HEK293-hP2X3 cells and their inhibition by ethanol and trichloroethanol

Membrane currents and changes in the intracellular Ca2+ concentration ([Ca2+]i) were measured in HEK293 cells transfected with the human P2X3 receptor (HEK293-hP2X3). RT-PCR and immunocytochemistry indicated the additional presence of endogenous P2Y1 and to some extent P2Y4 receptors. P2 receptor agonists induced inward currents in HEK293-hP2X3 cells with the rank order of potency alpha,beta-meATP approximately ATP > ADP-beta-S > UTP. A comparable rise in [Ca2+]i was observed after the slow superfusion of ATP, ADP-beta-S and UTP; alpha,beta-meATP was ineffective. These data, in conjunction with results obtained by using the P2 receptor antagonists TNP-ATP, PPADS and MRS2179 indicate that the current response to alpha,beta-meATP is due to P2X3 receptor activation, while the ATP-induced rise in [Ca2+]i is evoked by P2Y1 and P2Y4 receptor activation. TCE depressed the alpha,beta-meATP current in a manner compatible with a non-competitive antagonism. The ATP-induced increase of [Ca2+]i was much less sensitive to the inhibitory effect of TCE than the current response to alpha,beta-meATP. The present study indicates that in HEK293-hP2X3 cells, TCE, but not ethanol, potently inhibits ligand-gated P2X3 receptors and, in addition, moderately interferes with G protein-coupled P2Y1 and P2Y4 receptors. Such an effect may be relevant for the interruption of pain transmission in dorsal root ganglion neurons following ingestion of chloral hydrate or trichloroethylene.

Molecular mechanisms of analgesia induced by opioids and ethanol: is the GIRK channel one of the keys?

Opioids and ethanol have been used since ancient times for pain relief. Opioid signaling is mediated by various effectors, including G protein-activated inwardly rectifying potassium (GIRK) channels, adenylyl cyclases, voltage-dependent calcium channels, phospholipase Cbeta(PLCbeta), and mitogen-activated protein kinases, although it has been unclear which effector mediates the analgesic effects of opioids. Ethanol induces a variety of physiological phenomena via various proteins, including GIRK channels rather than via membrane lipids. GIRK channel activation by either G proteins or ethanol is impaired in weaver mutant mice. The mutant mice may therefore serve as a useful animal model for studying the role of GIRK channels in vivo. Reduced analgesia by using either opioids or ethanol in weaver mutant mice suggests that GIRK channels are important effectors in both opioid- and ethanol-induced analgesia. This hypothesis is supported by similar findings in GIRK2 knockout mice. Among the various effectors coupled with opioid receptors and various targets of ethanol, GIRK channels are the only molecules whose involvement in opioid- and ethanol-induced analgesia has been demonstrated in vivo. The GIRK channel is potentially one of the key molecules in furthering the understanding of the pain control system and in developing advanced analgesics with fewer adverse effects.

Effect of in vivo and in vitro ethanol on adrenergic and purinergic responses of the bisected rat vas deferens to low and high frequency pulses

1. This study investigates the effect of acute in vivo and in vitro ethanol administration on the contractions evoked electrically and by exogenous noradrenaline and alpha,beta-methylene-ATP in the rat bisected vas deferens. 2. In vivo ethanol treatment (3 g kg(-1), i.p.) significantly potentiated the early purinergic (phase I) and the delayed adrenergic (phase II) phases evoked by single-pulse stimulation of the epididymal portion of the rat vas deferens, leaving unaffected both phases in the prostatic portion. In vitro 50 mM ethanol significantly depressed phase I leaving unaffected phase II in both portions from untreated rats. In vitro ethanol significantly depressed phase I in the epididymal portion from in vivo ethanol treated animals and potentiated phase II in both portions. 3. In vivo ethanol treatment (3.0 g kg(-1), i.p.) selectively impaired the response to noradrenaline only in the prostatic portion of rat vas deferens while it was devoid of any action on alpha,beta-methylene-ATP contractions. Ethanol 50 mM in vitro was devoid of any action on the response to exogenous noradrenaline and alpha,beta-methylene-ATP in both tissues. 4. In vivo ethanol treatment slightly but significantly increased the phasic response in the epididymal portion to trains of stimuli (2-30 Hz). In vitro 50 mM ethanol was ineffective against the phasic and tonic contractions elicited by the tetanus in both portions. 5. It is concluded that ethanol treatment affects purinergic and adrenergic pathways of transmission possibly leading to a disruption of physiological contractions necessary to seminal emission.

Glucose deprivation and chemical hypoxia: neuroprotection by P2 receptor antagonists

In this work we investigate cell survival after glucose deprivation and/or chemical hypoxia and we analyse the neuroprotective properties of selected antagonists of P2 ATP receptors. We find that in rat cerebellar granule neurones, the antagonist basilen blue prevents neuronal death under hypoglycaemia. Basilen blue acts through a wide temporal range and it retains its efficacy under chemically induced hypoxic conditions, in the presence of the respiratory inhibitors of mitochondria electron transport chain complexes II (3-nitropropionic acid) and III (antimycin A). In spite of the presence of these compounds, basilen blue maintains normal intracellular ATP levels. It furthermore prevents neuronal death caused by agents blocking the mitochondrial calcium uptake (ruthenium red) or discharging the mitochondrial membrane potential (carbonyl cyanide m-chlorophenylhydrazone). Inhibition of poly (ADP-ribose) polymerase, modulation of the enzyme GAPDH and mitochondrial transport of mono-carboxylic acids are not conceivable targets for the action of basilen blue. Survival is sustained by basilen blue also in CNS primary cultures from hippocampus and in PNS sympathetic-like neurones. Partial neuroprotection is furthermore provided by three additional P2 receptor antagonists: suramin, pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid 4-sodium and 4,4'-diisothiocyanatostilbene-2,2'disulphonic acid. Our data suggest the exploitation of selected P2 receptor antagonists as potential neuroprotective agents.

Alteration of spontaneous firing rate of primary myelinated afferents by ATP in adjuvant-induced inflamed rats

The action of adenosine 5'-triphosphate (ATP) on primary myelinated mechanosensitive afferents was investigated in adjuvant-induced inflamed rats. ATP injected intravenously increased the spontaneous firing rate in most of the A fibers from sciatic nerve innervating inflamed hindpaw, whereas it affected only a few units in normal rats. The effects of ATP were blocked or attenuated by competitive P2 receptor antagonist suramin or reactive blue 2 in most of the fibers tested. Degranulation of mast cells with compound 48/80 did not change the response rate of afferents to ATP in inflamed rats while chemical sympathectomy with 6-hydroxydopamine decreased it to some extent, suggesting an involvement of sympathetic efferents in mediating ATP effects. The results support the view that ATP could change the activity of large mechanosensitive afferents via P2 receptors under state of inflammation, which may be related to touch-evoked pain.

Trichloroethanol inhibits ATP-induced membrane currents in cultured HEK 293-hP2X3 cells

Membrane currents in response to the application of alpha, beta-methylene ATP (alpha,beta-meATP) were recorded by the whole-cell patch-clamp technique in human embryonic kidney 293 cells transfected with the human P2X3 receptor (HEK 293-hP2X3 cells). Trichloroethanol, the biologically active metabolite of chloral hydrate, but not ethanol itself concentration-dependently and reversibly inhibited the current responses. It was concluded that the reported analgesic effect of chloral hydrate may be due to the interruption of pain transmission in dorsal root ganglia expressing P2X3 receptors.

Ethanol inhibition of adenosine 5'-triphosphate-activated current in freshly isolated adult rat hippocampal CA1 neurons

The effect of ethanol on current activated by extracellular adenosine 5'-triphosphate (ATP) was studied in freshly isolated adult rat hippocampal CA1 neurons using whole-cell patch-clamp recording. ATP activated an inward current with an EC(50) value of 18 microM. The inward current was also activated by 2-methylthio ATP (2-MeSATP) and alpha,beta-methylene ATP (alpha,beta-MeATP), inhibited by pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), and potentiated by Zn(2+). Ethanol inhibited current activated by 10 microM ATP with an IC(50) value of 83 mM in a voltage-independent manner. Ethanol, 100 mM, shifted the ATP concentration-response curve to the right, increasing the EC(50) value for ATP from 18 to 33 microM, but did not reduce the maximal response to ATP. The results suggest that ethanol can inhibit the function of P2X receptors in adult rat hippocampal neurons by decreasing the apparent affinity of the binding site for ATP.

Alcohol differentially affects noradrenergic and purinergic responses in the bisected rat vas deferens

This study investigates the effect of acute in vivo or in vitro ethanol administration on the adrenergic and purinergic responses in the epididymal and prostatic portion of rat vas deferens. Acute in vivo ethanol treatment (3.0 g/kg, i.p.) selectively impaired the response to noradrenaline in the prostatic portion of rat vas deferens, leaving unaffected the epididymal portion. In addition, the response evoked by the maximal concentration of alpha, beta-methylene-ATP was significantly depressed by acute in vivo ethanol treatment in both the epididymal and prostatic segments. Ethanol 50 mM in vitro was devoid of any action on the response to exogenous noradrenaline in both tissues. Ethanol in vitro left unaltered the response to alpha,beta-methylene-ATP in the epididymal portion, while potentiated the contractile response in the prostatic one. These results provide, for the first time, evidence that ethanol in vitro and in vivo differentially affects the noradrenergic and purinergic responses in the bisected vas deferens, suggesting that this substance may alter the male reproductive tract function.

Inhibition by ethanol of rat P2X(4) receptors expressed in Xenopus oocytes

1. The effect of ethanol on the function of P2X(4) receptors expressed in Xenopus oocytes was studied using two-electrode voltage-clamp recording. 2. The amplitude of current activated by 1 microM ATP was decreased by ethanol in a concentration-dependent manner over the concentration range 1 - 500 mM. The concentration of ethanol that produced 50% inhibition (IC(50)) of current activated by 1 microM ATP was 58 mM. 3. Ethanol inhibition of ATP-activated current was not dependent on membrane potential from -60 to +20 mV, and ethanol did not change the reversal potential of ATP-activated current. 4. Ethanol, 50 mM, shifted the ATP concentration-response curve to the right, increasing the EC(50) for ATP from 9.1 to 16.0 microM, but did not reduce the maximal response to ATP. 5. The results suggest that ethanol may inhibit P2X(4) receptors by decreasing the apparent affinity of the binding site for ATP. 6. Since the P2X(4) receptor is the most abundant P2X subunit in the brain, these receptors could be important effectors of ethanol action in the central nervous system.