51
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Ambrósio AF, Silva AP, Malva JO, Soares-da-Silva P, Carvalho AP, Carvalho CM. Inhibition of glutamate release by BIA 2-093 and BIA 2-024, two novel derivatives of carbamazepine, due to blockade of sodium but not calcium channels. Biochem Pharmacol 2001; 61:1271-5. [PMID: 11322931 DOI: 10.1016/s0006-2952(01)00584-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We investigated the mechanism(s) of action of two new putative antiepileptic drugs (AEDs), (S)-(-)-10-acetoxy-10,11-dihydro-5H-dibenz[b,f]azepine-5-carboxamide (BIA 2-093) and 10,11-dihydro-10-hydroxyimino-5H-dibenz[b,f]azepine-5-carboxamide (BIA 2-024), by comparing their effects on the release of endogenous glutamate in hippocampal synaptosomes, with those of carbamazepine (CBZ) and oxcarbazepine (OXC). The AEDs inhibited the release of glutamate evoked by 4-aminopyridine (4-AP) or veratridine in a concentration-dependent manner, being CBZ more potent than the other AEDs. Using conditions of stimulation (30 mM KCl), where Na(+) channels are inactivated, the AEDs did not inhibit either the Ca(2+)-dependent or -independent release of glutamate. The results indicate that BIA 2-093 and BIA 2-024 have sodium channel-blocking properties, but CBZ and OXC are more potent than the new AEDs. Moreover, the present data also indicate that Ca(2+) channels coupled to the exocytotic release of glutamate and the activity of the glutamate transporter were not affected by the AEDs.
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Affiliation(s)
- A F Ambrósio
- Department of Cell Biology, Center for Neuroscience of Coimbra, University of Coimbra, 3004-517, Coimbra, Portugal
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52
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Abstract
To clarify the mechanisms of interaction between adenosine A(1) receptor (A1-R) and adenosine A(2) receptor (A2-R) on neurotransmitter release, this study determined the functional interactions among adenosine receptors (AD-Rs), voltage-sensitive Ca(2+) channels (VSCCs), protein kinases (PKs), and synaptic proteins [N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors] on hippocampal serotonin release using in vivo microdialysis in freely moving rat. Basal serotonin release was regulated by two functional complexes: N-type VSCC (N-VSCC)/calcium-phospholipid-dependent protein kinase (PKC)/syntaxin (major pathway) and P-type VSCC (P-VSCC)/cyclic AMP-dependent protein kinase (PKA)/synaptobrevin (minor pathway). However, K(+)-evoked serotonin release was regulated by N-VSCC/PKC/syntaxin (minor pathway) and P-VSCC/PKA/synaptobrevin (major pathway). A1-R antagonists increased basal serotonin release, which was reduced by inhibitors of N-VSCC, PKC, and syntaxin predominantly and by inhibitors of PKA and synaptobrevin weakly, but was not affected by P-VSCC inhibitor. In the presence of A1-R antagonist, A2-R agonists increased basal serotonin release, which was inhibited by inhibitors of P-VSCC, PKA, and synaptobrevin predominantly and reduced by inhibitors of N-VSCC, PKC, and syntaxin weakly. Under the condition of activation of adenylate cyclase in the absence of A1-R antagonists, A2-R agonists increased basal serotonin release. A1-R antagonist and A2-R agonist enhanced K(+)-evoked serotonin release, which was inhibited by inhibitors of P-VSCC, PKA, and synaptobrevin predominantly. These results suggest that an activation of A1-R suppresses serotonin release via inhibition of both N-VSCC/PKC/syntaxin and P-VSCC/PKA/synaptobrevin pathways, and an activation of A2-R stimulates serotonin release via enhancement of the P-VSCC/PKA/synaptobrevin pathway. Therefore, PKA activity plays an important role in the interaction between A1-R and A2-R on hippocampal serotonin release.
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53
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Poli A, Di Iorio P, Beraudi A, Notari S, Zaccanti F, Villani L, Traversa U. The calcium-dependent [3H]acetylcholine release from synaptosomes of brown trout (Salmo trutta) optic tectum is inhibited by adenosine A1 receptors: effects of enucleation on A1 receptor density and cholinergic markers. Brain Res 2001; 892:78-85. [PMID: 11172751 DOI: 10.1016/s0006-8993(00)03229-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Presynaptic inhibition is one of the major control mechanisms in the CNS. Previously we reported that A1 adenosine receptors are highly concentrated in the brain, including optic tectum, of trout and that they inhibited the release of glutamate. The optic tectum is heavily innervated by cholinergic nerve terminals. We have investigated whether A1 receptors inhibit the presynaptic release of acetylcholine and whether the inhibition is triggered by calcium. The release of [3H]ACh evoked by 30 mM KCl was Ca2+ dependent and it was dose-dependently inhibited by the A1 adenosine receptor agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA) ranging between 10 nM to 100 microM. The maximum of inhibition was reached at 10 microM. The A1 receptor antagonist 8-cyclopentyltheopylline (CPT, 10 microM), reversed almost completely the inhibition induced by CCPA 10 microM. In Fura-2/AM loaded synaptosomes, K(+) depolarization raised [Ca2+](i) by about 64%. CCPA (10 microM) reduced the K(+)-evoked Ca2+ influx increase by about 48% and this effect was completely antagonised by CPT 10 microM. Synaptosome pretreatment with different Ca2+ channel blockers differently affected K(+)-evoked Ca2+ influx. This was not significantly modified by nifedipine (1 microM, L-type blocker) nor by omega-agatoxin IVA (0.3 microM, P/Q-type blocker), whereas about 50% reduction was shown by 0.5 microMomega-conotoxin GVIA (N-type blocker). Neurochemical parameters associated with cholinergic transmission and the density of A(1) adenosine receptors were measured in the trout optic tectum 12 days after unilateral eye ablation. A significant drop of both acetylcholinesterase (AChE) activity (24%) and choline acetyltransferase (CAT) activity (32%) was observed in deafferentated optic tectum, whereas the high affinity choline uptake did not parallel the decrease in enzyme activity. Eye ablation caused a marked decrease (43%) of A1 receptor density without changing the affinity. The K(+)-evoked release of [3H]ACh from synaptosomes of deafferentated was not modify as well as the efficacy of 10 microMCCPA in decreasing [3H]ACh release was not apparently modified.
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Affiliation(s)
- A Poli
- Department of Biology, University of Bologna, Via Selmi 3, 40126 Bologna, Italy.
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Cunha RA. Adenosine as a neuromodulator and as a homeostatic regulator in the nervous system: different roles, different sources and different receptors. Neurochem Int 2001; 38:107-25. [PMID: 11137880 DOI: 10.1016/s0197-0186(00)00034-6] [Citation(s) in RCA: 462] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Adenosine exerts two parallel modulatory roles in the CNS, acting as a homeostatic modulator and also as a neuromodulator at the synaptic level. We will present evidence to suggest that these two different modulatory roles are fulfilled by extracellular adenosine originated from different metabolic sources, and involve receptors with different sub-cellular localisation. It is widely accepted that adenosine is an inhibitory modulator in the CNS, a notion that stems from the preponderant role of inhibitory adenosine A(1) receptors in defining the homeostatic modulatory role of adenosine. However, we will review recent data that suggests that the synaptically localised neuromodulatory role of adenosine depend on a balanced activation of inhibitory A(1) receptors and mostly facilitatory A(2A) receptors. This balanced activation of A(1) and A(2A) adenosine receptors depends not only on the transient levels of extracellular adenosine, but also on the direct interaction between A(1) and A(2A) receptors, which control each other's action.
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Affiliation(s)
- R A Cunha
- Laboratory of Neurosciences, Faculty of Medicine, University of Lisbon, Portugal.
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Cunha RA, Almeida T, Ribeiro JA. Modification by arachidonic acid of extracellular adenosine metabolism and neuromodulatory action in the rat hippocampus. J Biol Chem 2000; 275:37572-81. [PMID: 10978314 DOI: 10.1074/jbc.m003011200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adenosine and arachidonate (AA) fulfil opposite modulatory roles, arachidonate facilitating and adenosine inhibiting cellular responses. To understand if there is an inter-play between these two neuromodulatory systems, we investigated the effect of AA on extracellular adenosine metabolism in hippocampal nerve terminals. AA (30 microm) facilitated by 67% adenosine evoked release and by 45% ATP evoked release. These effects were not significantly modified upon blockade of lipooxygenase or cyclooxygenase and were attenuated (52-61%) by the protein kinase C inhibitor, chelerythrine (6 microm). The ecto-5'-nucleotidase inhibitor, alpha,beta-methylene ADP (100 microm), caused a larger inhibition (54%) of adenosine release in the presence of AA (30 microm) compared with control (37% inhibition) indicating that the AA-induced extracellular adenosine accumulation is mostly originated from an increased release and extracellular catabolism of ATP. This AA-induced extracellular adenosine accumulation is further potentiated by an AA-induced decrease (48%) of adenosine transporters capacity. AA (30 microm) increased by 36-42% the tonic inhibition by endogenous extracellular adenosine of adenosine A(1) receptors in the modulation of acetylcholine release and of CA1 hippocampal synaptic transmission in hippocampal slices. These results indicate that AA increases tonic adenosine modulation as a possible feedback loop to limit AA facilitation of neuronal excitability.
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Affiliation(s)
- R A Cunha
- Laboratory of Neurosciences, Faculty of Medicine, and Department of Chemistry & Biochemistry, Faculty of Sciences, University of Lisbon, 1649-028 Lisbon, Portugal.
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Brown P, Dale N. Adenosine A1 receptors modulate high voltage-activated Ca2+ currents and motor pattern generation in the xenopus embryo. J Physiol 2000; 525 Pt 3:655-67. [PMID: 10856119 PMCID: PMC2269976 DOI: 10.1111/j.1469-7793.2000.00655.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Adenosine causes voltage- and non-voltage-dependent inhibition of high voltage-activated (HVA) Ca2+ currents in Xenopus laevis embryo spinal neurons. As this inhibition can be blocked by 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX) and mimicked by N6-cyclopentyladenosine (CPA) it appears to be mediated by A1 receptors. Agents active at A2 receptors either were without effect or could be blocked by DPCPX. AMP had no agonist action on these receptors. By using omega-conotoxin GVIA we found that adenosine inhibited an N-type Ca2+ current as well as a further unidentified HVA current that was insensitive to dihydropyridines, omega-agatoxin TK and omega-conotoxin MVIIC. Both types of current were subject to voltage- and non-voltage-dependent inhibition. We used CPA and DPCPX to test whether A1 receptors regulated spinal motor pattern generation in spinalized Xenopus embryos. DPCPX caused a near doubling of, while CPA greatly shortened, the length of swimming episodes. In addition, DPCPX slowed, while CPA greatly speeded up, the rate of run-down of motor activity. Our results demonstrate a novel action of A1 receptors in modulating spinal motor activity. Furthermore they confirm that adenosine is produced continually throughout swimming episodes and acts to cause the eventual termination of activity.
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Affiliation(s)
- P Brown
- School of Biological Sciences, Bute Medical Building, University of St Andrews, St Andrews, Fife KY16 9TS, UK
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Cunha RA, Ribeiro JA. Purinergic modulation of [(3)H]GABA release from rat hippocampal nerve terminals. Neuropharmacology 2000; 39:1156-67. [PMID: 10760359 DOI: 10.1016/s0028-3908(99)00237-3] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The hippocampal GABAergic system is assumed not to be a target for purine modulation. We have now confirmed that neither adenosine A(1) and A(3) receptor nor nucleotide P(2) or P(4) receptor activation modified the K(+)-evoked [(3)H]GABA release from hippocampal synaptosomes. However, activation of adenosine A(2A) receptors with CGS 21680 (10 nM) or HENECA (30 nM) facilitated GABA release by 32% and 21%, respectively. These effects were prevented by the A(2A) antagonist, ZM 241385 (20 nM). A(2A) receptors may activate adenylate cyclase and protein kinase A since CGS 21680 (10 nM) facilitation was partially prevented by 8-bromo-cAMP (1 mM), forskolin (10 microM) and HA-1004 (10 microM). Protein kinase C may also be recruited, since chelerythrine (6 microM) and phorbol-12, 13-didecanoate (250 nM) attenuated CGS 21680 (10 nM) facilitation of [(3)H]GABA release. Omega-agatoxin-IVA (200 nM) occluded CGS 21680 facilitation suggesting the involvement of P-type calcium channels. Thus, the adenosine A(2A) receptor system appears to be one of the first presynaptic neuromodulatory systems able to enhance the evoked release of GABA from hippocampal nerve terminals.
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Affiliation(s)
- R A Cunha
- University of Lisbon, Faculty of Medicine, Laboratory of Neurosciences, Av. Prof. Egas Moniz, 1649-028, Lisbon, Portugal.
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Masino SA, Mesches MH, Bickford PC, Dunwiddie TV. Acute peroxide treatment of rat hippocampal slices induces adenosine-mediated inhibition of excitatory transmission in area CA1. Neurosci Lett 1999; 274:91-4. [PMID: 10553945 DOI: 10.1016/s0304-3940(99)00693-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Brief exposure to conditions that generate free radicals inhibits synaptic transmission in hippocampal slices, most likely via a presynaptic mechanism. Because other physiologically stressful conditions that generate free radicals, such as hypoxia or ischemia, stimulate the release of adenosine from brain slices, we determined whether increases in extracellular adenosine mediate the presynaptic inhibition of excitatory transmission induced by peroxide treatment. Simultaneous addition of hydrogen peroxide (0.01%) and ferrous sulfate (100 microM) resulted in a >80% decrease in synaptic potentials recorded in the CA1 region of hippocampal slices of adult male rats. Treatment with theophylline (200 microM), a non-selective adenosine receptor antagonist, or 8-cyclopentyl-1,3-dipropylxanthine (100 nM), a selective adenosine A1 receptor antagonist, prior to and during hydrogen peroxide superfusion prevented the inhibition. These results demonstrate that acute exposure to hydrogen peroxide induces an adenosine-mediated decrease in synaptic transmission in hippocampal slices.
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Affiliation(s)
- S A Masino
- Department of Pharmacology and Neuroscience Program, UCHSC, Denver, CO 80262, USA.
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59
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Ambrósio AF, Silva AP, Malva JO, Soares-da-Silva P, Carvalho AP, Carvalho CM. Carbamazepine inhibits L-type Ca2+ channels in cultured rat hippocampal neurons stimulated with glutamate receptor agonists. Neuropharmacology 1999; 38:1349-59. [PMID: 10471089 DOI: 10.1016/s0028-3908(99)00058-1] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
In order to better understand the mechanism(s) of action of carbamazepine (CBZ), we studied its effects on the increase in [Ca2+]i and [Na+]i stimulated by glutamate ionotropic receptor agonists, in cultured rat hippocampal neurons, as followed by indo- or SBFI fluorescence, respectively. CBZ inhibited the increase in [Ca2+]i stimulated either by glutamate, kainate, alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), or N-methyl-D-aspartate (NMDA), in a concentration-dependent manner. In order to discriminate the effects of CBZ on the activation of glutamate receptors from possible effects on Ca2+ channels, we determined the inhibitory effects of Ca2+ channel blockers on [Ca2+]i changes in the absence or in the presence of CBZ. The presence of 1 microM nitrendipine, 0.5 microM omega-conotoxin GVIA (omega-CgTx GVIA), or of both blockers, inhibited the kainate-stimulated increase in [Ca2+]i by 51.6, 32.9 or 68.7%, respectively. In the presence of both 100 microM CBZ and nitrendipine, the inhibition was similar (54.1%) to that obtained with nitrendipine alone, but in the presence of both CBZ and omega-CgTx GVIA, the inhibition was greater (54%) than that caused by omega-CgTx GVIA alone. However, CBZ did not inhibit the increase in [Na+]i stimulated by the glutamate receptor agonists, but inhibited the increase in [Na+]i due to veratridine. Tetrodotoxin, or MK-801, did not inhibit the influx of Na+ stimulated by kainate, indicating that Na+ influx occurs mainly through the glutamate ionotropic non-NMDA receptors. Moreover, LY 303070, a specific AMPA receptor antagonist, inhibited the [Na+]i response to kainate or AMPA by about 70 or 80%, respectively, suggesting that AMPA receptors are mainly involved. Taken together, the results suggest that CBZ inhibits L-type Ca2+ channels and Na+ channels, but does not inhibit activation of glutamate ionotropic receptors.
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Affiliation(s)
- A F Ambrósio
- Department of Cell Biology, Center for Neuroscience of Coimbra and Faculty of Medicine, University of Coimbra, Portugal
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60
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Fowler JC, Gervitz L, Partridge LD. Hydroxylamine blocks pre- but not postsynaptic adenosine A(1) receptor-mediated actions in rat hippocampus. Brain Res 1999; 837:309-13. [PMID: 10434018 DOI: 10.1016/s0006-8993(99)01659-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The commonly used nitric oxide donor, hydroxylamine (NH(2)OH), can block or reverse the inhibition of glutamatergic transmission by adenosine or an adenosine A(1) agonist in rat hippocampal slice. In these experiments, hydroxylamine did not affect the adenosine A(1) receptor-mediated depression of postsynaptic excitability. We conclude that hydroxylamine acts presynaptically to counter adenosine A(1) receptor-mediated inhibition of synaptic transmission.
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Affiliation(s)
- J C Fowler
- Department of Physiology, Texas Tech University Health Sciences Center, School of Medicine, 3601 4th Street, Lubbock, TX 79430, USA.
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