Mast cell degranulation triggers hypersensitivity reactions at the body–environment interface. Adenosine modulates degranulation, but enhancement and inhibition have both been reported. Which of four adenosine receptors (ARs) mediate modulation, and how, remains uncertain. Also uncertain is whether adenosine reaches mast cell ARs by autocrine ATP release and ecto-enzymatic conversion. Uncertainties partly reflect species and cell heterogeneity, circumvented here by focusing on homogeneous human LAD2 cells. Quantitative PCR detected expression of A2A, A2B, and A3, but not A1, ARs. Nonselective activation of ARs with increasing NECA monotonically enhanced immunologically or C3a-stimulated degranulation. NECA alone stimulated degranulation slightly. Selective AR antagonists did not affect C3a-stimulated degranulation. NECA''s enhancement of C3a-triggered degranulation was partially inhibited by separate application of each selective antagonist, and abolished by simultaneous addition of antagonists to the three ARs. Only the A2A antagonist separately inhibited NECA''s enhancement of immunologically stimulated degranulation, which was abolished by simultaneous addition of the three selective antagonists. Immunological or C3a activation did not stimulate ATP release. NECA also enhanced immunologically triggered degranulation of mouse bone marrow derived mast cells (BMMCs), which was partially reduced only by simultaneous addition of the three antagonists or by the nonselective antagonist {"type":"entrez-protein","attrs":{"text":"CGS15943","term_id":"875345334"}}CGS15943. BMMCs also expressed A2A, A2B, and A3 ARs. but not A1AR detectably. We conclude that (a) A1AR is unnecessary for LAD2 degranulation or AR enhancement; (b) A2A, A2B, and A3 ARs all contribute to pharmacologic AR enhancement of LAD2 and BMMC degranulation; and (c) LAD2 cells depend on microenvironmental adenosine to trigger AR modulation. 相似文献
Adenosine, through A2A receptor (A2AR) activation, can act as a metamodulator, controlling the actions of other modulators, as brain-derived neurotrophic factor (BDNF). Most of the metamodulatory actions of adenosine in the hippocampus have been evaluated in excitatory synapses. However, adenosine and BDNF can also influence GABAergic transmission. We thus evaluated the role of A2AR on the modulatory effect of BDNF upon glutamate and GABA release from isolated hippocampal nerve terminals (synaptosomes). BDNF (30 ng/ml) enhanced K+-evoked [3H]glutamate release and inhibited the K+-evoked [3H]GABA release from synaptosomes. The effect of BDNF on both glutamate and GABA release requires tonic activation of adenosine A2AR since for both neurotransmitters, the BDNF action was blocked by the A2AR antagonist SCH 58261 (50 nM). In the presence of the A2AR agonist, {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 (30 nM), the effect of BDNF on either glutamate or GABA release was, however, not potentiated. It is concluded that both the inhibitory actions of BDNF on GABA release as well as the facilitatory action of the neurotrophin on glutamate release are dependent on the activation of adenosine A2AR by endogenous adenosine. However, these actions could not be further enhanced by exogenous activation of A2AR. 相似文献
Adenosine modulates dopamine in the brain via A1 and A2A receptors, but that modulation has only been characterized on a slow time scale. Recent studies have characterized a rapid signaling mode of adenosine that suggests a possible rapid modulatory role. Here, fast‐scan cyclic voltammetry was used to characterize the extent to which transient adenosine changes modulate stimulated dopamine release (5 pulses at 60 Hz) in rat caudate–putamen brain slices. Exogenous adenosine was applied and dopamine concentration monitored. Adenosine only modulated dopamine when it was applied 2 or 5 s before stimulation. Longer time intervals and bath application of 5 μM adenosine did not decrease dopamine release. Mechanical stimulation of endogenous adenosine 2 s before dopamine stimulation also decreased stimulated dopamine release by 41 ± 7%, similar to the 54 ± 6% decrease in dopamine after exogenous adenosine application. Dopamine inhibition by transient adenosine was recovered within 10 min. The A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine blocked the dopamine modulation, whereas dopamine modulation was unaffected by the A2A receptor antagonist SCH 442416. Thus, transient adenosine changes can transiently modulate phasic dopamine release via A1 receptors. These data demonstrate that adenosine has a rapid, but transient, modulatory role in the brain.
Brown or beige fat activation can cause potent anti-obesity and anti-diabetic effects. In a study recently published in Nature, Gnad et al. show that adenosine is a novel activator of brown and beige fat that acts through the A2A receptor.Brown fat is a thermogenic type of adipose tissue containing abundant mitochondria and multilocular lipid droplets, and is uniquely suited and required for cold tolerance and body weight control1. Upon brown fat activation, intracellular cyclic AMP (cAMP) levels rise rapidly, leading to lipolysis and upregulation of uncoupling protein 1 (UCP1) which initiates uncoupling of mitochondrial respiration and heat generation2,3. Additionally, beige or brite fat is a form of white fat that can be “browned” and induced to engage in respiratory uncoupling similarly as brown fat. Activated brown and beige fat consume substantial amounts of metabolic substrate, leading to powerful anti-obesity and anti-diabetic effects in mice. Adult humans possess brown and beige fat, making these tissues potentially important targets for treating obesity and metabolic diseases4. Activation of brown and beige fat occurs through several mechanisms including cold, adrenergic signaling, and hormone signaling4. However, a critical question remains of which pathway is altered therapeutically, as targeting these known activation pathways may cause discomfort, have undesirable side effects, or be insufficient alone to exert anti-obesity effects in humans. Thus, the need to discover novel pathways for brown and beige fat thermogenic activation persists.Adenosine is a purine nucleoside that alters cAMP signaling in several tissues5,6. There is a ubiquitous presence of adenosine in the extracellular space, and adenosine levels can be increased extracellularly or intracellularly through conversion of adenine nucleotides. Adenosine binds to four P1 G-protein-coupled receptor subtypes, which include the inhibitory receptors A1 and A3 and the stimulatory receptors A2A and A2B7. Inhibitory receptor activation leads to increased adenylate cyclase activity and decreased cAMP, while stimulatory receptor activation has the opposite effect. The distribution of the adenine receptor subtypes varies widely by tissue and species, and the response is dependent on the level of receptor expression, thus the actions of adenosine can be highly disparate depending on the tissue context8.In adipose tissue, adenosine was previously found to inhibit cAMP production in studies performed in hamster and rat, where oxygen consumption and lipolysis also decreased9,10. In a study recently published in Nature, Gnad et al.11 show that adenosine activates lipolysis and the thermogenic program in brown and white human and murine adipocytes (Figure 1). This phenomenon occurs at significantly lower concentrations of adenosine in brown adipocytes than in white adipocytes. The difference is accounted for by differential expression of the A2A receptor, which is highly expressed in human and murine brown fat relative to white fat. It is also due to the ratio of expression compared to the inhibitory A1 receptor, which is expressed at low levels in brown fat compared to white fat. Moreover, the authors show that hamster brown fat expresses almost equal amounts of A1 and A2A receptors, explaining the lack of activating effects of adenosine in those cells.Open in a separate windowFigure 1Adenosine activates brown or beige adipocytes through the A2A receptor. Adenosine activates the A2A receptor, leading to increased cAMP- and PGC-1α-dependent signaling that enhances thermogenesis and lipolysis in brown and beige adipocytes. Crosstalk occurs with adrenergic signaling, which increases cAMP and adenosine levels. Adenosine is released both through efflux from brown adipocytes and through breakdown of extracellular ATP by the ecto-5′-nucleotidase CD73. AR, adrenergic receptor.The determination of the source of the adenosine driving brown fat activation was also pursued. Adenosine could be derived from breakdown of ATP released from sympathetic neurons and brown adipocytes, or from brown adipocyte efflux of adenosine itself. The authors find that activated brown fat both releases adenosine through efflux and converts extracellular ATP to adenosine, as inhibition of the ecto-5′-nucleotidase CD73, which converts ATP to adenosine, only partially blocks the adenosine increase. Noradrenaline also enhances adenosine release from brown fat without any change in extracellular ATP, suggesting an intracellular crosstalk between catecholamine and adenosine signaling.The author further show that A2A receptor knockout mice exposed to cold exhibit defective thermogenesis, oxygen consumption, and lipolysis, demonstrating the importance of the A2A receptor in mediating the thermogenic response. Moreover, pharmacological activation with an A2A receptor agonist increases oxygen consumption in mice, while inhibition with a specific A2A antagonist decreases cold-induced oxygen consumption. A2A receptor agonism acts synergistically with noradrenaline in driving lipolysis, revealing an additive thermogenic effect of adenosine with catecholamine signaling. An A2A agonist protects against diet-induced obesity in mice, leading to increases in lean mass, oxygen consumption, glucose tolerance, and browning of white fat, which signifies the potential therapeutic importance of adenosine signaling. Importantly, overexpression of the A2A receptor in inguinal white fat increases its browning, indicating that bolstering of A2A adenosine receptor expression is sufficient to initiate a thermogenic response in the presence of physiological concentration of adenosine.This study reveals an endogenous purinergic signaling pathway that activates brown and beige fat. The critical signaling effector involved is cAMP, therefore the mechanism of activation is similar to those of other agents that act through the sympathetic nervous system or adrenergic signaling. It is unclear whether adenosine would contribute any additional anti-obesity effects than what has already been achieved with these other agents.While this study demonstrates substantial effects of adenosine on thermogenesis, further studies would better elucidate the specificity toward the A2A receptor in adipocytes. Treatment of A2A knockout mice with the receptor agonist would help demonstrate whether there are effects of the agonist independent of the A2A receptor in vivo. Additionally, adipose tissue-specific A2A knockout mice would reveal whether there are any phenotypic contributions from knockout in other tissues.Another question is whether A2A receptor agonism could be used chronically as an anti-obesity therapy in the clinic, since adenosine receptors are expressed in many tissues. This study did not explore the potentially confounding effects of A2A receptor agonism on tissues such as the brain or heart, including complications from vasodilation or cardiotoxicity. Indeed, A2A receptor antagonists have been used in clinical trials for Parkinson''s disease, highlighting the possible adverse effects of A2A receptor agonism on the brain. The effect of adenosine on lipolysis also raises the question of whether this pathway is involved in the lipoatrophy caused by nucleoside analogues used as anti-retroviral drugs. Nevertheless, this work adds important information about a cellular signaling pathway that may be leveraged in finding new therapies for obesity and metabolic diseases. 相似文献
The inhibitory effect of adenosine on platelet aggregation is abrogated after the addition of adenosine-deaminase. Inosine is a naturally occurring nucleoside degraded from adenosine.
Objectives
The mechanisms of antiplatelet action of adenosine and inosine in vitro and in vivo, and their differential biological effects by molecular modeling were investigated.
Results
Adenosine (0.5, 1 and 2 mmol/L) inhibited phosphatidylserine exposure from 52±4% in the control group to 44±4 (p<0.05), 29±2 (p<0.01) and 20±3% (p<0.001). P-selectin expression in the presence of adenosine 0.5, 1 and 2 mmol/L was inhibited from 32±4 to 27±2 (p<0.05), 14±3 (p<0.01) and 9±3% (p<0.001), respectively. At the concentrations tested, only inosine to 4 mmol/L had effect on platelet P-selectin expression (p<0.05). Adenosine and inosine inhibited platelet aggregation and ATP release stimulated by ADP and collagen. Adenosine and inosine reduced collagen-induced platelet adhesion and aggregate formation under flow. At the same concentrations adenosine inhibited platelet aggregation, decreased the levels of sCD40L and increased intraplatelet cAMP. In addition, SQ22536 (an adenylate cyclase inhibitor) and ZM241385 (a potent adenosine receptor A2A antagonist) attenuated the effect of adenosine on platelet aggregation induced by ADP and intraplatelet level of cAMP. Adenosine and inosine significantly inhibited thrombosis formation in vivo (62±2% occlusion at 60 min [n = 6, p<0.01] and 72±1.9% occlusion at 60 min, [n = 6, p<0.05], respectively) compared with the control (98±2% occlusion at 60 min, n = 6). A2A is the adenosine receptor present in platelets; it is known that inosine is not an A2A ligand. Docking of adenosine and inosine inside A2A showed that the main difference is the formation by adenosine of an additional hydrogen bond between the NH2 of the adenine group and the residues Asn253 in H6 and Glu169 in EL2 of the A2A receptor.
Conclusion
Therefore, adenosine and inosine may represent novel agents lowering the risk of arterial thrombosis. 相似文献
Summary The present study was designed to examine which type of adenosine receptors was involved in enhancement of high K+-evoked taurine release fromin vivo rat hippocampus using microdialysis. Perfusion with 0.5 or 5.0 mM adenosine enhanced high K+-evoked taurine release. Perfusion with 2M R(–)-N6-2-phenylisopropyladenosine (PIA), a selective adenosine A1 receptor agonist, did not modulate taurine release. Perfusion with 1M 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), a selective adenosine A1 receptor antagonist, increased taurine release. On the other hand, perfusion with 20M 2-[4-(2-carboxyethyl)phenethylamino]-5-N-ethyl-carboxamideadenosine (CGS21680), a selective adenosine A2A receptor agonist, enhanced taurine release, while perfusion with 1 mM 3,7-dimethyl-propagylxanthine (DMPX), an adenosine A2 receptor antagonist, did not affect taurine release. These results demonstrate that adenosine enhances high K+-evoked taurine release via activation of adenosine A2A receptors from both neurons and glial cells ofin vivo rat hippocampus. 相似文献
Benign prostatic hypertrophy has been related with glandular ischemia processes and adenosine is a potent vasodilator agent. This study investigates the mechanisms underlying the adenosine-induced vasorelaxation in pig prostatic small arteries. Adenosine receptors expression was determined by Western blot and immunohistochemistry, and rings were mounted in myographs for isometric force recording. A2A and A3 receptor expression was observed in the arterial wall and A2A-immunoreactivity was identified in the adventitia–media junction and endothelium. A1 and A2B receptor expression was not obtained. On noradrenaline-precontracted rings, P1 receptor agonists produced concentration-dependent relaxations with the following order of potency: 5′-N-ethylcarboxamidoadenosine (NECA) = {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 > 2-Cl-IB-MECA = 2-Cl-cyclopentyladenosine = adenosine. Adenosine reuptake inhibition potentiated both NECA and adenosine relaxations. Endothelium removal and ZM241385, an A2A antagonist, reduced NECA relaxations that were not modified by A1, A2B, and A3 receptor antagonists. Neuronal voltage-gated Ca2+ channels and nitric oxide (NO) synthase blockade, and adenylyl cyclase activation enhanced these responses, which were reduced by protein kinase A inhibition and by blockade of the intermediate (IKCa)- and small (SKCa)-conductance Ca2+-activated K+ channels. Inhibition of cyclooxygenase (COX), large-conductance Ca2+-activated-, ATP-dependent-, and voltage-gated-K+ channel failed to modify these responses. These results suggest that adenosine induces endothelium-dependent relaxations in the pig prostatic arteries via A2A purinoceptors. The adenosine vasorelaxation, which is prejunctionally modulated, is produced via NO- and COX-independent mechanisms that involve activation of IKCa and SKCa channels and stimulation of adenylyl cyclase. Endothelium-derived NO playing a regulatory role under conditions in which EDHF is non-functional is also suggested. Adenosine-induced vasodilatation could be useful to prevent prostatic ischemia. 相似文献
Glaucoma, a leading cause of blindness worldwide, is an optic neuropathy commonly associated with elevated intraocular pressure (IOP). The major goals of glaucoma treatments are to lower IOP and protect retinal ganglion cells. It has been revealed recently that adenosine and adenosine receptors (ARs) have important roles in IOP modulation and neuroprotection.
Scope of review
This article reviews recent studies on the important roles of adenosine and ARs in aqueous humor formation and outflow facility, IOP and retinal neuroprotection.
Major conclusions
Adenosine and several adenosine derivatives increase and/or decrease IOP via A2A AR. Activation of A1 AR can reduce outflow resistance and thereby lower IOP, A3 receptor antagonists prevent adenosine-induced activation of Cl− channels of the ciliary non-pigmented epithelial cells and thereby lower IOP. A1 and A2A agonists can reduce vascular resistance and increase retina and optic nerve head blood flow. A1 agonist and A2A antagonist can enhance the recovery of retinal function after ischemia attack. Adenosine acting at A3 receptors can attenuate the rise in calcium and retinal ganglion cells death accompanying P2X(7) receptor activation.
General significance
Evidence suggested that the adenosine system is one of the potential target systems for therapeutic approaches in glaucoma. 相似文献
Adenosine modulates the survival of chick embryo retinal neurons in culture. When cultures were incubated for 3 days and refed with fresh medium, a large proportion of neurons died in the subsequent 3 days of culture. This cell death was prevented by preincubation of cultures for at least 24h with adenosine plus the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), an adenosine uptake blocker nitrobenzylthioinosine (NBI), the adenosine A2A receptor agonist 2-[4-(2-carboxyethyl) phenethylamino]-5-N-ethylcarboxamidoadenosine (CGS21680), or the permeant cyclic AMP analog 8-bromo cyclic AMP, but not the A1 receptor agonist cyclohexyladenosine (CHA). Adenosine deaminase induced cell death when added to culture medium, and this effect was prevented by EHNA. Cell death was not observed when the medium was replaced by a conditioned medium from sister cultures. The data strongly suggest that adenosine regulates the survival of developing retinal neurons by a long-term activation of A2A receptors and the increase of cyclic AMP levels. 相似文献
1. In rat ileal smooth muscle both adenosine and ATP at 10−4 M significantly enhanced spontaneous mechanical activity. The excitatory actions of adenosine were blocked by the P1 receptor antagonist 8-phenyltheophylline and the excitatory effects of ATP were significantly reduced by the P2 receptor antagonist quinidine.2. The P2 receptor desensitizer α,β-methylene-ATP was without effect on ACh responses nor did the stable analogue β,gg-methylene-ATP exert any effect on spontaneous mechanical activity.3. Pretreatment with adenosine caused a dose-dependent enhancement of K-induced contractures in the ileum. Low adenosine concentrations slightly inhibited and high concentrations slightly enhanced ACh-induced contractures in the ileum.4. ATP potentiated the phasic component of the ileal K-induced contracture but strongly inhibited tonic force at high concentrations. This agent slightly inhibited the phasic component of the ACh-induced contracture while strongly inhibiting ACh-induced tonic force.5. α,β-methylene-ATP inhibited ileal muscle ACh induced contractures while it potentiated both phasic and tonic K-induced contractures. β, γ-methylene ATP inhibited ACh-induced contractures but it enhanced K-induced phasic contractures while inhibiting K-induced tonic force.6. The results of this study suggest that rat ileum may contain the A1 subtype of the P1 receptor but the evidence for a P2 receptor subtype is conflicting despite the inhibition of ATP actions by quinidine.7. The inhibition of K- and ACh-induced tonic force suggests that adenosine and ATP interactions with ileal smooth muscle may inactivate slow voltage-dependent calcium channels leading to EC uncoupling. 相似文献
Adenosine has been found to be cardioprotective during episodes of cardiac ischemia/reperfusion through activation of the A1 and possibly A3 receptors. Therefore, we have investigated whether activation of these receptors can protect also against apoptotic death induced by angiotensin II (Ang II) in neonatal rat cardiomyocyte cultures. Exposure to Ang II (10 nM) resulted in a 3-fold increase in programmed cell death (p < 0.05). Pretreatment with the A1 adenosine receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 1 M), abolished the effects of Ang II on programmed cardiomyocyte death. Moreover, exposure of cells to the A1 adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) before pretreatment with CCPA, prevented the protective effect of the latter. Pretreatment with the A3 adenosine receptor agonist N6-(3-iodobenzyl) adenosine-5-N-methyluronamide (IB-MECA, 0.1 M), led to a partial decrease in apoptotic rate induced by Ang II. Exposure of myocytes to Ang II caused an immediate increase in the concentration of intracellular free Ca2+ that lasted 40–60 sec. Pre-treatment of cells with CCPA or IB-MECA did not block Ang II-induced Ca2+ elevation. In conclusion, activation of adenosine A1 receptors can protect the cardiac cells from apoptosis induced by Ang II, while activation of the adenosine A3 receptors confers partial cardioprotection. 相似文献
Caffeine, a stimulant largely consumed around the world, is a non-selective adenosine receptor antagonist, and therefore caffeine actions at synapses usually, but not always, mirror those of adenosine. Importantly, different adenosine receptors with opposing regulatory actions co-exist at synapses. Through both inhibitory and excitatory high-affinity receptors (A1R and A2R, respectively), adenosine affects NMDA receptor (NMDAR) function at the hippocampus, but surprisingly, there is a lack of knowledge on the effects of caffeine upon this ionotropic glutamatergic receptor deeply involved in both positive (plasticity) and negative (excitotoxicity) synaptic actions. We thus aimed to elucidate the effects of caffeine upon NMDAR-mediated excitatory post-synaptic currents (NMDAR-EPSCs), and its implications upon neuronal Ca2+ homeostasis. We found that caffeine (30–200 μM) facilitates NMDAR-EPSCs on pyramidal CA1 neurons from Balbc/ByJ male mice, an action mimicked, as well as occluded, by 1,3-dipropyl-cyclopentylxantine (DPCPX, 50 nM), thus likely mediated by blockade of inhibitory A1Rs. This action of caffeine cannot be attributed to a pre-synaptic facilitation of transmission because caffeine even increased paired-pulse facilitation of NMDA-EPSCs, indicative of an inhibition of neurotransmitter release. Adenosine A2ARs are involved in this likely pre-synaptic action since the effect of caffeine was mimicked by the A2AR antagonist, SCH58261 (50 nM). Furthermore, caffeine increased the frequency of Ca2+ transients in neuronal cell culture, an action mimicked by the A1R antagonist, DPCPX, and prevented by NMDAR blockade with AP5 (50 μM). Altogether, these results show for the first time an influence of caffeine on NMDA receptor activity at the hippocampus, with impact in neuronal Ca2+ homeostasis.
The latero-capsular part of the central nucleus of the amygdala (CeLC) is the target of the spino-parabrachio-amygdaloid pain pathway. Our previous studies showed that CeLC neurons develop synaptic plasticity and increased neuronal excitability in the kaolin/carrageenan model of arthritic pain. These pain-related changes involve presynaptic group I metabotropic glutamate receptors (mGluRs) and postsynaptic NMDA and calcitonin gene-related peptide (CGRP1) receptors. Here we address the role of group II mGluRs.
Results
Whole-cell current- and voltage-clamp recordings were made from CeLC neurons in brain slices from control rats and arthritic rats (>6 h postinjection of kaolin/carrageenan into the knee). Monosynaptic excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation of afferents from the pontine parabrachial (PB) area. A selective group II mGluR agonist (LY354740) decreased the amplitude of EPSCs more potently in CeLC neurons from arthritic rats (IC50 = 0.59 nM) than in control animals (IC50 = 15.0 nM). The inhibitory effect of LY354740 was reversed by a group II mGluR antagonist (EGLU) but not a GABAA receptor antagonist (bicuculline). LY354740 decreased frequency, but not amplitude, of miniature EPSCs in the presence of TTX. No significant changes of neuronal excitability measures (membrane slope conductance and action potential firing rate) were detected.
Conclusion
Our data suggest that group II mGluRs act presynaptically to modulate synaptic plasticity in the amygdala in a model of arthritic pain. 相似文献
Sensory stimuli evoke responses in cerebellar Purkinje cells (PCs) via the mossy fiber-granule cell pathway. However, the properties of synaptic responses evoked by tactile stimulation in cerebellar PCs are unknown. The present study investigated the synaptic responses of PCs in response to an air-puff stimulation on the ipsilateral whisker pad in urethane-anesthetized mice.
Methods and Main Results
Thirty-three PCs were recorded from 48 urethane-anesthetized adult (6–8-week-old) HA/ICR mice by somatic or dendritic patch-clamp recording and pharmacological methods. Tactile stimulation to the ipsilateral whisker pad was delivered by an air-puff through a 12-gauge stainless steel tube connected with a pressurized injection system. Under current-clamp conditions (I = 0), the air-puff stimulation evoked strong inhibitory postsynaptic potentials (IPSPs) in the somata of PCs. Application of SR95531, a specific GABAA receptor antagonist, blocked IPSPs and revealed stimulation-evoked simple spike firing. Under voltage-clamp conditions, tactile stimulation evoked a sequence of transient inward currents followed by strong outward currents in the somata and dendrites in PCs. Application of SR95531 blocked outward currents and revealed excitatory postsynaptic currents (EPSCs) in somata and a temporal summation of parallel fiber EPSCs in PC dendrites. We also demonstrated that PCs respond to both the onset and offset of the air-puff stimulation.
Conclusions
These findings indicated that tactile stimulation induced asynchronous parallel fiber excitatory inputs onto the dendrites of PCs, and failed to evoke strong EPSCs and spike firing in PCs, but induced the rapid activation of strong GABAA receptor-mediated inhibitory postsynaptic currents in the somata and dendrites of PCs in the cerebellar cortex Crus II in urethane-anesthetized mice. 相似文献
Adenosine plays a dual role on acetylcholine (ACh) release from myenteric motoneurons via the activation of high-affinity inhibitory A1 and facilitatory A2A receptors. The therapeutic potential of adenosine-related compounds for controlling intestinal motility and inflammation, prompted us to investigate further the role of low-affinity adenosine receptors, A2B and A3, on electrically-evoked (5 Hz, 200 pulses) [3H]ACh release from myenteric neurons. Immunolocalization studies showed that A2B receptors exhibit a pattern of distribution similar to the glial cell marker, GFAP. Regarding A1 and A3 receptors, they are mainly distributed to cell bodies of ganglionic myenteric neurons, whereas A2A receptors are localized predominantly on cholinergic nerve terminals. Using selective antagonists (DPCPX, ZM241385 and MRS1191), data indicate that modulation of evoked [3H]ACh release is balanced through tonic activation of inhibitory (A1) and facilitatory (A2A and A3) receptors by endogenous adenosine. The selective A2B receptor antagonist, PSB603, alone was devoid of effect and failed to modify the inhibitory effect of NECA. The A3 receptor agonist, 2-Cl-IB MECA (1–10 nM), concentration-dependently increased the release of [3H]ACh. The effect of 2-Cl-IB MECA was attenuated by MRS1191 and by ZM241385, which selectively block respectively A3 and A2A receptors. In contrast to 2-Cl-IB MECA, activation of A2A receptors with CGS21680C attenuated nicotinic facilitation of ACh release induced by focal depolarization of myenteric nerve terminals in the presence of tetrodotoxin. Tandem localization of excitatory A3 and A2A receptors along myenteric neurons explains why stimulation of A3 receptors (with 2-Cl-IB MECA) on nerve cell bodies acts cooperatively with prejunctional facilitatory A2A receptors to up-regulate acetylcholine release. The results presented herein consolidate and expand the current understanding of adenosine receptor distribution and function in the myenteric plexus of the rat ileum, and should be taken into consideration for data interpretation regarding the pathophysiological implications of adenosine on intestinal motility disorders. 相似文献
Adenosine and its metabolite, inosine, have been described as molecules that participate in regulation of inflammatory response. The aim of this study was to investigate the effect of adenosine and inosine in a mouse model of carrageenan-induced pleurisy as well as the participation of adenosine receptors in this response. Injection of carrageenan into the pleural cavity induced an acute inflammatory response characterized by leukocyte migration, pleural exudation, and increased release of interleukin-1β and tumor necrosis factor-α in pleural exudates. The treatment with adenosine (0.3–100 mg/kg, i.p.) and inosine (0.1–300 mg/kg, i.p.) 30 min before carrageenan injection reduced significantly all these parameters analyzed. Our results also demonstrated that A2A and A2B receptors seem to mediate the adenosine and inosine effects observed, since pretreatment with selective antagonists of adenosine A2A (ZM241385) and A2B (alloxazine) receptors, reverted the inhibitory effects of adenosine and inosine in pleural inflammation. The involvement of A2 receptors was reinforced with adenosine receptor agonist {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 treatment, since its anti-inflammatory effects were reversed completely and partially with ZM241385 and alloxazine injection, respectively. Moreover, the combined treatment with subeffective dose of adenosine (0.3 mg/kg) and inosine (1.0 mg/kg) induced a synergistic anti-inflammatory effect. Thus, based on these findings, we propose that inosine contributes with adenosine to exert anti-inflammatory effects in pleural inflammation, reinforcing the notion that endogenous nucleosides play an important role in controlling inflammatory diseases. This effect is likely mediated by the activation of adenosine A2 subtype receptors and inhibition of production or release of pro-inflammatory cytokines. 相似文献
The role of pannexin 1 in the release to the extracellular space of ATP/adenosine modulating the acetylcholine (ACh) secretion was studied in mouse diaphragm motor synapses. Using neuromuscular preparations obtained from wild-type and pannexin-1 knockout mice, the miniature endplate potential (MEPPs) and evoked endplate potentials (EPPs) were recorded in combination with pharmacological modulation of P2-type ATP receptors and A1-type adenosine receptors. Selective inhibition of A1 receptors with DPCPX or P2 receptors with PPADS increased quantal content of EPPs in wild-type mice. MRS 2211, selective antagonist of P2Y13 receptors, produced the same effect. Activation of receptors A1 or P2Y13 by their agonists (2-CADO and IDP, respectively) decreased the EPP quantal content. It means that the activity of endogenous ATP and adenosine is synergistic and directed to depression of the ACh release. ARL67156, an inhibitor of synaptic ecto-ATPases, which blocks the hydrolysis of ATP to adenosine and increases the level of ATP in the synaptic cleft, prolonged EPPs without changing their quantal content. In pannexin-1 knockout mice there were no changes in the EPP quantal content and in other parameters of synaptic transmission as compared to wildtype mice. However, downregulation of purinergic effects with antagonists of A1 or P2 receptors (DPCPX, PPADS, MRS 2211) did not change EPP quantal content and any other parameters of spontaneous or evoked ACh release in all cases. ARL67156 did not alter the temporal parameters of EPPs, either. Nevertheless, 2-CADO, the A1-type receptor agonist, decreased the EPP quantal content, while the agonist of P2Y13 receptors decreased the MEPP amplitude. Thus, in mice lacking pannexin 1, procedures revealing the presence and regulatory activity of synaptic ATP/adenosine did not change the parameters of synaptic transmission. The obtained data substantiate a mandatory role of pannexin 1 in the purinergic regulation of motor synapse activity by endogenous ATP/adenosine. 相似文献
N6-2-(4-aminophenyl)ethyladenosine (APNEA) is a nonselective adenosine receptor agonist known to have a high affinity for the adenosine A1 and A3 receptors. It was found to be able to dose-dependently increase the sustained (4 min) Ca2+ influx into rat cortical synaptosomes while 2-chloro-N6-(3-iodobenzyl)-adenosine-5-N-methyluronamide (Cl-IB-MECA), a selective A3 agonist has no effect. However, this effect of APNEA was not affected by the presence of 8-cyclopentyl-l,3-dimethylxanthine (CPT), a selective A1 antagonist; but instead completely abolished by 8-(3-chlorostyryl)caffeine (CSC), a selective A2a antagonist, or -conotoxin GVIA. These results show that in the rat cortex, presynaptic A2a receptors can mediate neurotransmitter release by increasing Ca2+ influx through the N-type calcium channels. A1 and A3 receptors appear not to be involved. 相似文献
AimsWe investigated the effects induced by exogenous adenosine on the spontaneous contractile activity of the longitudinal muscle of a mouse ileum, the receptor subtypes activated, the involvement of enteric nerves and whether opening of K+ channels was a downstream event leading to the observed effects.Main methodsMechanical responses of the mouse ileal longitudinal muscle to adenosine were examined in vitro as changes in isometric tension.Key findingsAdenosine caused a concentration-dependent reduction of the spontaneous contraction amplitude of the ileal longitudinal muscle up to its complete disappearance. This effect induced was markedly reduced by an A1 receptor antagonist, but not by A2 and A3 receptor antagonists and mimicked only by the A1 receptor agonist. Adenosine uptake inhibitors did not change adenosine potency. A1 receptor expression was detected at the smooth muscle level. Adenosine responses were insensitive to tetrodotoxin, atropine or nitric oxide synthase inhibitor. Tetraethylammonium and iberiotoxin, BKCa channel blockers, significantly reduced adenosine effects, whilst 4-aminopyridine, a Kv blocker, apamin, a small conductance Ca2+-activated K+ (SKCa) channel blocker, charybdotoxin, an intermediate conductance Ca2+-activated K+ (IKCa) and BKCa channel blocker, or glibenclamide, an ATP-sensitive K+ channel blocker, had no effects. The combination of apamin plus iberiotoxin caused a reduction of the purinergic effects greater than iberiotoxin alone.SignificanceAdenosine acts as an inhibitory modulator of the contractility of mouse ileal longitudinal muscle through postjunctional A1 receptors, which in turn would induce opening of BKCa and SKCa potassium channels. This study would provide new insight in the pharmacology of purinergic receptors involved in the modulation of the gastrointestinal contractility. 相似文献