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1.
The intent of the present study was to investigate adenosine receptor sites in brain membranes of the saltwater teleost fish, Mullus surmuletus, using the A 1 receptor selective agonist, [ 3H]CHA, and A 2a receptor selective agonist [ 3H]CGS 21680. The A 1 selective agonist, [ 3H]CHA, bound saturably, reversibly and with high affinity to a single-class of binding sites (K d 1.47 nM; B max 100–190 fmol/mg protein, dependent on fish length). The A 2a selective agonist, [ 3H]CGS 21680, also bound saturably, reversibly and with relative high affinity to a single-class of binding sites (K d 44.2 nM; B max 150–300 fmol/mg protein dependent on fish length). In equilibrium competition experiments, adenosine analogous, NECA, CGS 21680, CHA, CPA, S-PIA, R-PIA, CPCA, DPMA, and xanthine antagonists, DPCPX, XAC, and THEO all displaced [ 3H]CHA and [ 3H]CGS 21680 specifically bound to brain membranes from Mullus surmuletus. Specific binding of both [ 3H]CHA and [ 3H]CGS 21680 was inhibited by GDPβS. For [ 3H]CHA the IC 50 value was 2.5 ± 0.1 μM, while for [ 3H]CGS 21680 the IC 50 value was 7.7 ± 0.3 μM. Our results indicate that the high affinity binding sites for [ 3H]CHA have some pharmacological characteristics of mammalian A 1 adenosine receptors, while the binding sites for [ 3H]CGS 21680 appear to be virtually identical to the binding sites for [ 3H]CHA. 相似文献
2.
Little is known about the mechanisms that regulate the expression of adenosine receptors during CNS development. We demonstrate here that retinas from chick embryos injected in ovo with selective adenosine receptor ligands show changes in A1 receptor expression after 48 h. Exposure to A1 agonist N 6‐cyclohexyladenosine (CHA) or antagonist 8‐Cyclopentyl‐1, 3‐dipropylxanthine (DPCPX) reduced or increased, respectively, A1 receptor protein and [ 3H]DPCPX binding, but together, CHA+DPCPX had no effect. Interestingly, treatment with A 2A agonist 3‐[4‐[2‐[[6‐amino‐9‐[(2R,3R,4S,5S)‐5‐(ethylcarbamoyl)‐3,4‐dihydroxy‐oxolan‐2‐yl]purin‐2‐yl]amino] ethyl]phenyl] propanoic acid (CGS21680) increased A1 receptor protein and [ 3H]DPCPX binding, and reduced A 2A receptors. The A 2A antagonists 7‐(2‐phenylethyl)‐5‐amino‐2‐(2‐furyl)‐pyrazolo‐[4,3‐e]‐1,2,4‐trizolo[1,5‐c] pyrimidine (SCH58261) and 4‐(2‐[7‐amino‐2‐[2‐furyl][1,2,4]triazolo[2,3‐a][1,3,5]triazo‐5‐yl‐amino]ethyl)phenol (ZM241385) had opposite effects on A1 receptor expression. Exposure to CGS21680 + CHA did not change A1 receptor levels, whereas CHA + ZM241385 or CGS21680 + DPCPX had no synergic effect. The blockade of adenosine transporter with S‐(4‐nitrobenzyl)‐6‐thioinosine (NBMPR) also reduced [ 3H]DPCPX binding, an effect blocked by DPCPX, but not enhanced by ZM241385. [ 3H]DPCPX binding kinetics showed that treatment with CHA reduced and CGS21680 increased the Bmax, but did not affect Kd values. CHA, DPCPX, CGS21680, and ZM241385 had no effect on A1 receptor mRNA. These data demonstrated an in vivo regulation of A1 receptor expression by endogenous adenosine or long‐term treatment with A1 and A 2A receptors modulators. 相似文献
3.
The adenosine A 2B receptor is the least well characterized of the four adenosine subtypes due to the lack of potent and selective agonists and antagonists. Despite the widespread distribution of A 2B receptor mRNA, little information is available with regard to their function. The characterization of A 2B receptors, through radioligand binding studies, has been performed, until now, by using low-affinity and non-selective antagonists like 1,3-dipropyl-8-cyclopentylxanthine ([ 3H]DPCPX),(4-(2-[7-amino-2-(2-furyl)-[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl)-phenol ([ 3H]ZM 241385) and 3-(3,4-aminobenzyl)-8-(4-oxyacetate)phenyl-1-propyl-xanthine ([ 125I]ABOPX). Recently, high-affinity radioligands for A 2B receptors, [N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)-phenoxy]acetamide ([ 3H]MRS 1754), N-(2-(2-Phenyl-6-[4-(2,2,3,3-tetratritrio-3-phenylpropyl)-piperazine-1-carbonyl]-7H-pyrrolo[2,3-d]pyrimidin-4-ylamino)-ethyl)-acetamide ([ 3H]OSIP339391) and N-benzo[1,3]dioxol-5-yl-2-[5-(1,3-dipropyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]-acetamide] ([ 3H]MRE 2029F20), have been introduced. This minireview offers an overview of these recently developed radioligands and the most important applications of drugs towards A 2B receptors. 相似文献
4.
Adenosine A 2B receptors of native human and rodent cell lines were investigated using [ 3H]PSB-298 [(8-{4-[2-(2-hydroxyethylamino)-2-oxoethoxy]phenyl}-1-propylxanthine] in radioligand binding studies. [ 3H]PSB-298 showed saturable and reversible binding. It exhibited a K D value of 60 ± 1 nM and limited capacity (B max = 3.511 fmol per milligram protein) at recombinant human adenosine A 2B receptors expressed in human embryonic kidney cells (HEK-293). The addition of sodium chloride (100 mM) led to a threefold increase in the number of binding sites recognized by the radioligand. The curve of the agonist 5′-N-ethylcarboxamidoadenosine (NECA) was shifted to the right in the presence of NaCl, while the curve of the antagonist PSB-298 was shifted to the left, indicating that PSB-298 may be an inverse agonist at A 2B receptors. Adenosine A 2B receptors were shown to be the major adenosine A 2 receptor subtype on the mouse neuroblastoma x rat glioma hybrid cell line NG108-15 cells. Binding studies at rat INS-1 cells (insulin secreting cell line) demonstrated that [ 3H]PSB-298 is a selective radioligand for adenosine A 2B binding sites in this cell line. 相似文献
5.
Inhibitory and stimulatory adenosine receptors have been identified and characterized in both membranes and intact rat C6
glioma cells. In membranes, saturation experiment performed with [ 3H]DPCPX, selective A 1R antagonist, revealed a single binding site with a K
D = 9.4 ± 1.4 nM and B
max = 62.7 ± 8.6 fmol/mg protein. Binding of [ 3H]DPCPX in intact cell revealed a K
D = 17.7 ± 1.3 nM and B
max = 567.1 ± 26.5 fmol/mg protein. On the other hand, [ 3H]ZM241385 binding experiments revealed a single binding site population of receptors with K
D = 16.5 ± 1.3 nM and B
max = 358.9 ± 52.4 fmol/mg protein in intact cells, and K
D = 4.7 ± 0.6 nM and B
max = 74.3 ± 7.9 fmol/mg protein in plasma membranes, suggesting the presence of A 2A receptor in C6 cells. A 1, A 2A, A 2B and A 3 adenosine receptors were detected by Western-blotting and immunocytochemistry, and their mRNAs quantified by real time PCR
assays. Giα and Gsα proteins were also detected by Western-blotting and RT-PCR assays. Furthermore, selective A 1R agonists inhibited forskolin- and GTP-stimulated adenylyl cyclase activity and CGS 21680 and NECA stimulated this enzymatic
activity in C6 cells. These results suggest that C6 glioma cells endogenously express A 1 and A 2 receptors functionally coupled to adenylyl cyclase inhibition and stimulation, respectively, and suggest these cells as a
model to study the role of adenosine receptors in tumoral cells. 相似文献
6.
Binding properties of the subtypes of adenosine A2 receptors in membrane preparations and the effects of adenosine receptor ligands on cAMP accumulation in slices from the optic tectum of neonatal chicks have been investigated. [ 3H]2-[4-(2-p-carboxyethyl)phenylamino]-5'-N-ethylcarboxaminoadenosine (CGS 21680), a selective ligand for adenosine A2a receptors, did not bind to optic tectal membranes, as observed with rat striatal membranes. CGS 21680 also did not induce cyclic AMP accumulation in optic tectum slices. However, 5'-N-ethylcarboxamidoadenosine (NECA), 2-chloro-adenosine or adenosine induced a 2.5- to 3-fold increase on cyclic AMP accumulation in this preparation. [ 3H]NECA binds to fresh non-washed-membranes obtained from optic tectum of chicks, displaying one population of binding sites, which can be displaced by NECA, 8-phenyltheophylline, 2-chloro-adenosine, but is not affected by CGS 21680. The estimated K D value was 400.90 ± 80.50 nM and the B max was estimated to be 2.51 ± 0.54 pmol/mg protein. Guanine nucleotides, which modulate G-proteins activity intracellularly, are also involved in the inhibition of glutamate responses by acting extracellularly. Moreover, we have previously reported that guanine nucleotides potentiate, while glutamate inhibits, adenosine-induced cyclic AMP accumulation in slices from optic tectum of chicks. However, the guanine nucleotides, GMP or GppNHp and the metabotropic glutamate receptors agonist, 1S,3R-ACPD did not alter the [ 3H]NECA binding observed in fresh non-washed-membranes. Therefore, the adenosine A2 receptor found in the optic tectum must be the adenosine A2b receptor which is available only in fresh membrane preparations, and its not modulated by guanine nucleotides or glutamate analogs. 相似文献
7.
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. A 2A and A 3 receptor expression was observed in the arterial wall and A 2A-immunoreactivity was identified in the adventitia–media junction and endothelium. A 1 and A 2B 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 A 2A antagonist, reduced NECA relaxations that were not modified by A 1, A 2B, and A 3 receptor antagonists. Neuronal voltage-gated Ca 2+ 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 (IK Ca)- and small (SK Ca)-conductance Ca 2+-activated K + channels. Inhibition of cyclooxygenase (COX), large-conductance Ca 2+-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 A 2A purinoceptors. The adenosine vasorelaxation, which is prejunctionally modulated, is produced via NO- and COX-independent mechanisms that involve activation of IK Ca and SK Ca 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
8.
A recently identified novel Gα olf variant, XLGα olf, is shown to functionally couple to the human adenosine A 2A receptor (A 2AR). In Sf9 cells expressing A 2AR, β1, and γ2, co-expression of XLGα olf increased NECA-induced [ 35S]GTPγS binding from approximately 130% to 300% of basal levels. Pharmacological characteristics of A 2AR ligands on these cells were evaluated by using [ 3H]ZM241385- and [ 35S]GTPγS- binding assays. The rank order of the equilibrium binding constants (K d or K i) of adenosine receptor ligands were [ 3H]ZM241385 ≈ CGS15943 < MRS1220 < < CV1808 ≈ NECA < CGS21680 ≈ adenosine < IBMECA < HEMADO ≈ CPA ≈ CCPA. The rank order of EC 50 values for agonists were CV1808 ≈ NECA < adenosine ≈ CGS26180 < IBMECA < HEMADO ≈ CPA ≈ CCPA. This pharmacology is consistent with the literature for A 2AR and suggests that Sf9 cells co-expressing A 2AR, β1, γ2, and XLGα olf could serve as a heterologous expression system for A 2AR drug screening. 相似文献
9.
6-Hydroxydopamine (6-OHDA) is the most used toxin in experimental Parkinson’s disease (PD) models. 6-OHDA shows high affinity for the dopamine transporter and once inside the neuron, it accumulates and undergoes non-enzymatic auto-oxidation, promoting reactive oxygen species (ROS) formation and selective damage of catecholaminergic neurons. In this way, our group has established a 6-OHDA in vitro protocol with rat striatal slices as a rapid and effective model for screening of new drugs with protective effects against PD. We have shown that co-incubation with guanosine (GUO, 100 μM) prevented the 6-OHDA-induced damage in striatal slices. As the exact GUO mechanism of action remains unknown, the aim of this study was to investigate if adenosine A1 (A1R) and/or A2A receptors (A2AR) are involved on GUO protective effects on striatal slices. Pre-incubation with DPCPX, an A1R antagonist prevented guanosine effects on 6-OHDA-induced ROS formation and mitochondrial membrane potential depolarization, while CCPA, an A1R agonist, did not alter GUO effects. Regarding A2AR, the antagonist SCH58261 had similar protective effect as GUO in ROS formation and mitochondrial membrane potential. Additionally, SCH58261 did not affect GUO protective effects. The A2AR agonist CGS21680, although, completely blocked GUO effects. Finally, the A1R antagonist DPCPX, and the A2AR agonist CGS21680 also abolished the preventive guanosine effect on 6-OHDA-induced ATP levels decrease. These results reinforce previous evidence for a putative interaction of GUO with A1R-A2AR heteromer as its molecular target and clearly indicate a dependence on adenosine receptors modulation to GUO protective effect. 相似文献
10.
Adenosine, through A 2A receptor (A 2AR) 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 A 2AR 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 A 2AR since for both neurotransmitters, the BDNF action was blocked by the A 2AR antagonist SCH 58261 (50 nM). In the presence of the A 2AR 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 A 2AR by endogenous adenosine. However, these actions could not be further enhanced by exogenous activation of A 2AR. 相似文献
11.
Guanine nucleotides (GN) have been implicated in many intracellular mechanisms. Extracellular actions, probably as glutamate receptor antagonists, have also been recently attributed to these compounds. GN may have a neuroprotective role by inhibiting excitotoxic events evoked by glutamate. Effects of extracellular GN on adenosine-evoked cellular responses have also been reported. However, the exact mechanism of such interaction is not known. In the present study, we showed that GN potentiated adenosine-induced cAMP accumulation in slices of hippocampus from young rats. However, neither GMP nor the metabotropic glutamate receptor agonist, 1S,3R-ACPD, inhibited the binding of the adenosine receptor agonist [ 3H]NECA (when binding to adenosine A2 receptors), or the binding of the adenosine A2a receptor agonist [ 3H]CGS 21680 in hippocampal membrane preparations. GppNHp, probably by interacting with G-proteins, decreased [ 3H]CGS 21680 binding. [ 3H]GMP binding was assayed in order to evaluate the GN sites which are not G-proteins. [ 3H]GMP binding was inhibited by GMP and GppNHp, but not by 1S,3R-ACPD. The interaction of endogenous adenosine with the GMP-binding sites was determined by incubating membranes in the presence or absence of adenosine deaminase (ADA). NECA, CADO, CGS 21680 and CPA (only at the highest concentration used) increased GMP binding in the presence of ADA. However, in the absence of ADA, the control levels of GMP binding were as high as in the presence of added ADA plus adenosine agonists, indicating that endogenous adenosine modulates the binding of GMP. If this site has a neuroprotective role, adenosine may be increasing its neuromodulator and proposed protective action. 相似文献
12.
5-Hydroxytryptamine 2A (5-HT 2A) receptor kinetics was studied in cerebral cortex and brain stem of streptozotocin (STZ) induced diabetic rats. Scatchard analysis with [ 3H] (±) 2,3dimethoxyphenyl-1-[2-(4-piperidine)-methanol] ([ 3H]MDL100907) in cerebral cortex showed no significant change in maximal binding (B max) in diabetic rats compared to controls. Dissociation constant (K d) of diabetic rats showed a significant decrease (p < 0.05) in cerebral cortex, which was reversed to normal by insulin treatment. Competition studies of [ 3H]MDL100907 binding in cerebral cortex with ketanserin showed the appearance of an additional low affinity site for 5-HT 2A receptors in diabetic state, which was reversed to control pattern by insulin treatment. In brain stem, scatchard analysis showed a significant increase (p < 0.05) in B max accompanied by a significant increase (p < 0.05) in K d. Competition analysis in brain stem also showed a shift in affinity towards a low affinity State for 5-HT 2A receptors. All these parameters were reversed to control level by insulin treatment. These results show that in cerebral cortex there is an increase in affinity of 5-HT 2A receptors without any change in its number and in the case of brain stem there is an increase in number of 5HT 2A receptors accompanied by a decrease in its affinity during diabetes. Thus, from the results we suggest that the increase in affinity of 5-HT 2A receptors in cerebral cortex and upregulation of 5-HT 2A receptors in brain stem may lead to altered neuronal function in diabetes. 相似文献
13.
Abstract: Rat medullary brain segments containing primarily nucleus tractus solitarius (NTS) were used for superfusion studies of evoked transmitter release and for isotherm receptor binding assays. Isotherm binding assays with [ 3H]CGS-21680 on membranes prepared from NTS tissue blocks indicated a single high-affinity binding site with a KD of 5.1 ± 1.4 n M and a Bmax of 20.6 ± 2.4 fmol/mg of protein. The binding density for [ 3H]CGS-21680 on NTS membranes was 23 times less than comparable binding on membranes from striatal tissue. Electrically stimulated (1 min at 25 mA, 2 ms, 3 Hz) release of [ 3H]norepinephrine ([ 3H]NE) from 400-µm-thick NTS tissue slices resulted in an S 2/S 1 ratio of 0.96 ± 0.02. Superfusion of single tissue slices with 0.1–100 n M CGS-21680, a selective adenosine A 2a receptor agonist, for 5 min before the S 2 stimulus produced a significant concentration-dependent increase in the S 2/S 1 fractional release ratio that was maximal (31.3% increase) at 1.0 n M. However, superfusion of tissue slices with CGS-21680 over the same concentration range for 20 min before the S 2 stimulus did not alter the S 2/S 1 ratio significantly from control release ratios. The augmented release of [ 3H]NE mediated by 1.0 n M CGS-21680 with a 5-min tissue exposure was abolished by 1.0 and 10 n M CGS-15943 as well as by 100 n M 8-(3-chlorostyryl)caffeine, both A 2a receptor antagonists, but not by 1.0 n M 8-cyclopentyl-1,3-dipropylxanthine, the A 1 receptor antagonist. Taken together, these results suggest that CGS-21680 augmented the evoked release of [ 3H]NE in the NTS via activation of presynaptic A 2a receptors within the same concentration range as the binding affinity observed for [ 3H]CGS-21680. It was also apparent that this population of presynaptic adenosine A 2a receptors in the NTS desensitized within 20 min because the augmenting action of CGS-21680 on evoked transmitter release was not evident at the longer interval. 相似文献
14.
The neuromodulator adenosine is acting through specific receptors coupled to adenylate cyclase via G-proteins. The expression of both adenosine receptors A 1 and A 2 as well as forkolin binding sites was investigated by radioligand binding techniques in 8-day-old neurons isolated from fetal rat forebrain and cultured in chemically-defined medium. Adenosine A 1 receptors were specifically labeled with [ 3H]chloro-N 6-cyclopentyladenosine (CCPA), whereas [ 3H]CGS 21680 was used for the analysis of A 2 receptors. Cultured neurons exhibited high affinity binding sites for CCPA (Bmax=160 fmol/mg protein; Kd=2.9 nM), and for CGS 21680 (Bmax=14 fmol/mg protein; Kd=1.7 nM). These data correlate well with those obtained in crude membranes isolated from the newborn rat forebrain. The incubation of culture membranes in the additional presence of guanylyl-5-imidodiphosphate (Gpp(NH)p, a GTP analogue) led to significantly increased Kd-values, suggesting the association of adenosine receptors with G-proteins. Finally, cultured neurons also bound specifically [ 3H]forskolin with characteristics close to those found in the newborn brain, indicating that cultured neurons appear as an appropriate model for studying the neuromodulatory properties of adenosine. 相似文献
15.
Summary 1. Adenoregulin is an amphilic peptide isolated from skin mucus of the tree frog, Phyllomedusa bicolor. Synthetic adenoregulin enhanced the binding of agonists to several G-protein-coupled receptors in rat brain membranes.2. The maximal enhancement of agonist binding, and in parentheses, the concentration of adenoregulin affording maximal enhancement were as follows: 60% (20 µM) for A 1-adenosine receptors, 30% (100 µM) for A 2a-adenosine receptors, 20% (2 µM) for
2-adrenergic receptors, and 30% (100 µM) for 5HT 1A receptors. High affinity agonist binding for A 1-,
2-, and 5HT 1A-receptors was virtually abolished by GTP S in the presence of adenoregulin, but was only partially abolished in its absence. Magnesium ions increased the binding of agonists to receptors and reduced the enhancement elicited by adenoregulin.3. The effect of adenoregulin on binding of N 6-cyclohexyladenosine ([ 3H]CHA) to A 1-receptors was relatively slow and was irreversible. Adenoregulin increased the B max value for [ 3H]CHA binding sites, and the proportion of high affinity states, and slowed the rate of [ 3H]CHA dissociation. Binding of the A 1-selective antagonist, [ 3H]DPCPX, was maximally enhanced by only 13% at 2 µM adenoregulin. Basal and A 1-adenosine receptor-stimulated binding of [ 35S]GTP S were maximally enhanced 45% and 23%, respectively, by 50 µM adenoregulin. In CHAPS-solubilized membranes from rat cortex, the binding of both [ 3H]CHA and [ 3H]DPCPX were enhanced by adenoregulin. Binding of [ 3H]CHA to membranes from DDT 1 MF-2 cells was maximally enhanced 17% at 20 µM adenoregulin. In intact DDT 1 MF-2 cells, 20 µM adenoregulin did not potentiate the inhibition of cyclic AMP accumulation mediated via the adenosine A 1 receptor.4. It is proposed that adenoregulin enhances agonist binding through a mechanism involving enhancement of guanyl nucleotide exchange at G-proteins, resulting in a conversion of receptors into a high affinity state complexed with guanyl nucleotide-free G-protein. 相似文献
16.
The excitatory glutamatergic neurons in the hippocampus are modulated by inhibitory GABA-releasing interneurons. The neuromodulator adenosine is known to inhibit the presynaptic release of neurotransmitters and to hyperpolarize postsynaptic neurons in the hippocampus, which would imply that it is an endogenous protective agent against cerebral ischemia and excitotoxic neuronal damage. Interactions of the GABAergic and adenosinergic systems in regulating neuronal excitability in the hippocampus is of crucial importance, particularly under cell-damaging conditions. We now characterized the effects of adenosine receptor agonists and antagonists on the release of preloaded [ 3H]GABA from hippocampal slices prepared from adult (3-month-old) mice, using a superfusion system. The effects were tested both under normal conditions and in ischemia induced by omitting glucose and oxygen from the superfusion medium. Basal and K +-evoked GABA release in the hippocampus were depressed by adenosinergic compounds. Under normal conditions activation of both adenosine A 1 and A 2A receptors by the agonists R(-) N6-(2-phenylisopropyl)adenosine and CGS 21680 inhibited the K +-evoked release, which effects were blocked by their specific antagonists, 8-cyclopentyl-1,3-dipropyl-xanthine and 3,7-dimethyl-1-propargylxanthine, respectively. Under ischemic conditions the release of both GABA and adenosine is markedly enhanced. The above receptor agonists then depressed both the basal and K +-evoked GABA release, only the action of A 2A receptors being however receptor-mediated. The demonstrated depression of GABA release by adenosine in the hippocampus could be deleterious to neurons and contribute to excitotoxicity. 相似文献
17.
Adenosine plays a dual role on acetylcholine (ACh) release from myenteric motoneurons via the activation of high-affinity inhibitory A 1 and facilitatory A 2A 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, A 2B and A 3, on electrically-evoked (5 Hz, 200 pulses) [ 3H]ACh release from myenteric neurons. Immunolocalization studies showed that A 2B receptors exhibit a pattern of distribution similar to the glial cell marker, GFAP. Regarding A 1 and A 3 receptors, they are mainly distributed to cell bodies of ganglionic myenteric neurons, whereas A 2A 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 (A 1) and facilitatory (A 2A and A 3) receptors by endogenous adenosine. The selective A 2B receptor antagonist, PSB603, alone was devoid of effect and failed to modify the inhibitory effect of NECA. The A 3 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 A 3 and A 2A receptors. In contrast to 2-Cl-IB MECA, activation of A 2A 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 A 3 and A 2A receptors along myenteric neurons explains why stimulation of A 3 receptors (with 2-Cl-IB MECA) on nerve cell bodies acts cooperatively with prejunctional facilitatory A 2A 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
18.
AbstractThe binding characteristics of radiolabeled N 6-(cyclohexyl)adenosine ([ 3H]CHA), N 6-(R-phenylisopropyl)adenosine ([ 3H]R-PIA), 5′-N-ethylcarboxamidoadenosine ([ 3H]NECA), and 2-[4-(2-carboxyethyl)phenyl]ethyl-amino-5′-N-ethylcarboxamidoadenosine ([ 3H]CGS 21680), to rat testis membranes were investigated. Specific binding of [ 3H]CGS 21680, a selective agonist for the A 2a adenosine receptor, was very modest whilst the nonselective agonist [ 3H]NECA bound to rat testis membranes showing high binding capacity. At least two types of binding sites for [ 3H]NECA could be identified in rat testis membranes: high affinity sites and high capacity sites. Selective agonists for the At adenosine receptor, [ 3H]CHA and [ 3H]R-PIA bound with high affinity to a single class of binding sites. This high affinity binding site showed the typical pharmacological specificity of the A 1 adenosine receptor with a potency order for agonists of CHA R-PIA > NECA > N 6-(S-phenylisopropyl)adenosine (S-PIA). In order to detect the presence of the A 3 adenosine receptor in these membranes we selectively blocked the A 1 receptor with a large molar excess of a xanthine antagonist, either 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) or xanthine amine congener (XAC). In the presence of an antagonist a low affinity binding site for [ 3H]CHA and [ 3H]R-PIA was detected. This low affinity binding site showed a different pharmacological specificity than the high affinity binding site. In fact the potency order for agonists was CHA NECA = R-PIA > S-PIA. This finding suggests that the low affinity binding site represents the A 3 adenosine receptor. 相似文献
19.
The release of the inhibitory amino acid taurine is markedly enhanced under ischemic conditions in both adult and developing
brain stem, together with a pronounced increase in the release of the neuromodulator adenosine. We now studied the effects
of adenosine receptor agonists and antagonists on [ 3H]taurine release in the brain stem in normoxia and ischemia, using a superfusion system. Under standard conditions, the adenosine
A 1 receptor agonist N 6-cyclohexyladenosine (CHA) potentiated basal taurine release in adult mice, which response was blocked by the antagonist 8-cyclopentyl-1,3-dipropylxanthine
(DPCPX). CHA and the A 2a receptor agonist 2- p-(2-carboxyethyl)phenylamino-5′- N-ethylcarboxaminoadenosinehydrochloride (CGS 21680) had no effect on the release in developing mice. In ischemia, CHA depressed
both basal and K +-stimulated taurine release in developing mice in a receptor-mediated manner, blocked by DPCPX. The A 2a receptor agonist CGS 21680 was also inhibitory. Taurine and adenosine may thus not cooperate in developing mice to prevent
ischemic neuronal damage. On the other hand, CGS 21680 enhanced taurine release in the adult brain stem in ischemia, both
basal and K +-stimulated release being affected. These effects were abolished by the antagonist 3,7-dimethyl-1-propargylxanthine (DMPX),
indicating a receptor-mediated process. In this case elevated levels of taurine could be beneficial, protecting against hyperexcitation
and excitotoxicity. 相似文献
20.
Abstract: The modulation by adenosine analogues and endogenous adenosine of the electrically evoked release of [ 3H]acetylcholine ([ 3H]ACh) was compared in subslices of the three areas of the rat hippocampus (CA1, CA3, and dentate gyrus). The mixed A 1/A 2 agonist 2-chloroadenosine (CADO; 2–10 µ M) inhibited, in a concentration-dependent manner, the release of [ 3H]ACh from the three hippocampal areas, being more potent in the CA1 and CA3 areas than in the dentate gyrus. The inhibitory effect of CADO (5 µ M) on [ 3H]ACh release was prevented by the A 1 antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 50 n M) in the three hippocampal areas and was converted in an excitatory effect in the CA3 and dentate gyrus areas. The A 2A agonist CGS-21680 (30 n M) produced a greater increase of the evoked release of [ 3H]ACh in the CA3 than in the dentate gyrus areas, whereas no consistent effect was found in the CA1 area or in the whole hippocampal slice. The excitatory effect of CGS-21680 (30 n M) in the CA3 area was prevented by the adenosine receptor antagonist 3,7-dimethyl-1-propargylxanthine (10 µ M). Both adenosine deaminase (2 U/ml) and DPCPX (250 n M) increased the evoked release of [ 3H]ACh in the CA1 and CA3 areas but not in the dentate gyrus. The amplitude of the effect of DPCPX and adenosine deaminase was similar in the CA1 area, but in the CA3 area DPCPX produced a greater effect than adenosine deaminase. It is concluded that the electrically evoked release of [ 3H]ACh in the three areas of the rat hippocampus can be differentially modulated by adenosine. In the CA1 area, only A 1 inhibitory receptors modulate ACh release, whereas in the CA3 area, both A 2A excitatory and A 1 inhibitory adenosine receptors modulate ACh release. In the dentate gyrus, both A 1 inhibitory and A 2A excitatory adenosine receptors are present, but endogenous adenosine does not activate them. 相似文献
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