Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The single-locus mutant mouse tottering (tg) displays spontaneous seizures that resemble those in human petit-mal epilepsy. In order to examine alterations in GABAA receptor function which could arise as a result of this mutation, the influx of 36Cl- was determined using microsacs (membrane vesicles) isolated from the brain of tg/tg and coisogenic C57BL/6J (+/+) control mice. In microsacs from both tg/tg and +/+ strains, the maximum level of 36Cl- uptake induced by 50 microM GABA was observed during five seconds of incubation at 28 degrees C. Compared to +/+, the GABA-dependent 36Cl- uptake in tg/tg microsacs was significantly lower and faded rapidly during longer incubations. The levels of gated 36Cl- uptake in tg/tg microsacs were 45 +/- 6.3%, 65 +/- 9.9%, and 33 +/- 6.1% of control (+/+) values for 3-, 5-, and 10-s incubations, respectively. GABAA receptor-specific agonists (30 microM), muscimol, isoguvacine and THIP (4,5,6,7-tetrahydroisoazolo-[5,4-c]pyridin-3-ol) induced 36Cl- influx in the order muscimol > GABA > isoguvacine > THIP. This order was similar for both strains, but the agonist-dependent influx was always significantly lower in tg/tg compared to +/+. Treatment of the microsacs with 10 microM H-89, a membrane-permeant inhibitor of the cAMP-dependent protein kinase (protein kinase A, PKA), was without effect on GABA-gated 36Cl- uptake in +/+, but increased the gated uptake in tg/tg microsacs by 44 +/- 16%. PKA was assayed using [gamma-32]ATP and kemptide as the substrate. Triton X-100 (0.1%) increased both the basal and 8-Br-cAMP dependent PKA activity in microsacs by 3-4 four fold, showing that most of the enzyme was intravesicular. In the presence of Triton, the basal activity of PKA in the tg/tg preparations was twice that of +/+, while the strain difference was no longer apparent in assays containing 8-Br-cAMP. The data suggest that an abnormal elevation of protein kinase A activity in tottering mouse brain contributes to an impairment of GABAA receptor function. It is suggested that the resulting loss of inhibition could play a role in induction of the seizures which characterize the mutant phenotype.
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PMID:Reduced function of gamma-aminobutyric acidA receptors in tottering mouse brain: role of cAMP-dependent protein kinase. 856 63

1. Intracellular recordings were used to study the role of metabotropic glutamate receptors (mGluRs) in modulating GABA-mediated giant depolarizing potentials (GDPs) in immature rat hippocampal CA3 neurones. 2. The mGluR antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG, 1 mM) reduced the frequency of GDPs. The broad-spectrum ionotropic glutamate receptor antagonist kynurenic acid (1 mM) blocked GDPs. 3. In the presence of kynurenic acid, both tetanic stimulation of the hilus or bath application of quisqualic acid (1 microM) and trans-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD, 20 microM) induced the appearance of GDPs. These effects were antagonized by MCPG (1 mM) or L(+)-2-amino-3-phosphonopropionic acid (L-AP3) and blocked by bicuculline (10 microM). 4. 8-Bromo-cAMP (8-Br-cAMP, 0.3 mM), 3-isobutyl-1-methylxanthine (IBMX, 200 microM) or forskolin (30 microM) mimicked the effects of mGluR agonists on GDPs. The forskolin analogue 1,9-dideoxyforskolin (30 microM), which does not activate adenylate cyclase, was ineffective. 5. Incubation of slices in the presence of the protein kinase A inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPS) (500 microM) or superfusion of Rp-cAMPS (20 microM) prevented the effects of forskolin or t-ACPD on GDPs. In the presence of kynurenic acid, the protein kinase C activator, phorbol 12,13-diacetate (2 microM) induced the appearance of GDPs. This effect was prevented by staurosporine (1 microM). However, staurosporine (1-3 microM) did not modify the effects of t-ACPD on GDPs. 6. It is suggested that, during development, mGluRs enhance the synchronous release of GABA, responsible for GDPs, through cAMP-dependent protein kinase.
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PMID:Cyclic AMP-dependent modulation of giant depolarizing potentials by metabotropic glutamate receptors in the rat hippocampus. 858 96

The effects of serotonin (5-HT) and GABA on two Ca2+ currents, a transient low-voltage-activated current (tLVA) and a sustained high-voltage-activated current (sHVA) were examined in isolated photoreceptors of Hermissenda. The sHVA current was blocked by 5-HT and reduced by activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate. The effects of 5-HT were transiently reversed by staurosporine and partially blocked by the PKC inhibitor peptide [PKC(19-36)]. GABA enhanced both the tLVA and sHVA currents at low concentrations (5 nM to 5 microM) and reduced the sHVA current at high concentrations (>10 microM). The GABA-mediated enhancement of the Ca2+ current at low concentrations was sensitive to block by picrotoxin. The protein kinase A (PKA) inhibitor peptide [PKI(6-22)amide] blocked enhancement of both Ca2+ currents produced by cAMP analogs and GABA, suggesting that the effects at low concentrations may be PKA mediated. Caged GTP-gamma-S released by flash photolysis reduced the sHVA current, and pretreatment of the photoreceptors with pertussis toxin blocked the effects of higher concentrations of GABA, indicating that at higher concentrations, the effects may be G-protein mediated.
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PMID:Protein kinase and G-protein regulation of Ca2+ currents in Hermissenda photoreceptors by 5-HT and GABA. 876 66

The aim of the present work was to investigate the mechanism by which the diffusible factor nitric oxide regulates GABAA receptor function in the brain. The effect of nitric oxide on GABAA receptor function has been studied in two different neuronal preparations: rat cerebral cortex microsacs and rat cerebellum granule cells in culture. In the first case, GABA-stimulated 36Cl-accumulation was studied as an index of GABAA receptor function. The maximal rate of GABA-stimulated 36Cl- accumulation (Vmax) was reduced by treatment of microsacs with nitric oxide chemical donors such as sodium nitroprusside (-26%) and S-nitroso-acetyl-penicillamine (-11%). The greater effect of the former agent is due to an additional interference by its breakdown products. The biochemical precursor L-arginine (1 mM) produced the same Vmax decrease as S-nitroso-acetyl-penicillamine. This effect was reversed by a nitric oxide synthase blocker and appears truly nitric oxide mediated. The action of nitric oxide in this system does not seem to imply cyclic GMP formation. GABAA receptor function was studied by whole-cell patch-clamp in rat cerebellum granule cells in culture. In this case, L-arginine (100 microM) profoundly reduced the Cl- current elicited by 10 microM GABA and its effect subsided following washing out. The effect of L-arginine was observed almost exclusively on the rapidly desensitizing component of the GABA-activated current. The action of L-arginine was blocked by a protein kinase G inhibitor and mimicked by its activators. Thus, it appears that this effect in these cells involves nitric oxide formation, cyclic GMP accumulation and protein kinase G-catalysed phosphorylation of GABAA receptor.
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PMID:Nitric oxide and GABAA receptor function in the rat cerebral cortex and cerebellar granule cells. 884 80

Involvement of cyclic AMP-dependent protein kinase in the desensitization of GABAB receptor expressed in Xenopus oocytes was studied. GABA produced an outward current in the presence of bicuculline, under voltage-clamp conditions. Baclofen mimicked the effect of GABA, thereby indicating that the response to GABA in the presence of bicuculline is mediated by stimulation of GABAB receptor. The GABAB receptor-mediated response was suppressed by dibutyric cyclic AMP and forskolin, but not by 1,9-dideoxy-forskolin, and the effect of dibutyric cyclic AMP was inhibited by H-8. Application of GABA for 1 min at 20-min intervals induced a reliable response, while that at 10-min intervals produced a desensitization. The desensitization was also partially prevented by H-8. Dibutyric cyclic GMP, 8-bromo-cyclic GMP and Na-nitroprusside did not affect the GABAB receptor-mediated response. Thus, cyclic AMP-dependent protein kinase, but not cyclic GMP-dependent protein kinase participates in desensitization of the GABAB receptor expressed in Xenopus oocytes.
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PMID:Desensitization by cyclic AMP-dependent protein kinase of GABAB receptor expressed in Xenopus oocytes. 884 60

GABAB receptors affect short-term signalling in various cell types. However, nothing is known about possible long-term effects on transcription. To analyse such effects in the CNS, we studied GABAB receptor-mediated gene regulation in primary cultures of cerebellar granule neurons. Transcription was followed using a chloramphenicol acetyl transferase reporter gene driven by the minimal cyclic AMP-responsive element (TGACGTCA). Transcription was stimulated by activation of both the cyclic AMP (forskolin: 5 x 10(-6) M) and the Ca2+ dependent (KCl: 30 mM) pathways (-)-Baclofen (10(-6) M to 10(-4) M), a specific GABAB receptor agonist, reduced by 50-70% the transcriptional stimulation evoked by both forskolin and KCl, whereas isoguvacine, a GABAA receptor agonist, was without effect. Moreover, the GABAB antagonist CGP 35348 abrogated the inhibitory effects of both GABA and baclofen, indicating that GABAB receptors were specifically implicated in this response. Measurements of cyclic AMP levels suggested that (-) baclofen inhibits forskolin-initiated transcription by reducing cyclic AMP production. Direct transcriptional activation, via the cyclic AMP pathway, by overexpression of the catalytic subunit of the cyclic AMP-dependent protein kinase, was not significantly altered by (-) baclofen. This indicates again that (-) baclofen-dependent inhibitory mechanisms operate upstream of cyclic AMP-dependent protein kinase at the level of second messenger formation. Further, we used a yeast transcriptional activator GAL4-cyclic AMP-responsive element binding protein to analyse whether GABAB receptor-mediated inhibition of cyclic AMP-responsive element transcription implicated the transacting factor cyclic AMP-responsive element binding protein. We show that the negative effects of (-) baclofen implicate this transcription factor and this holds good for both the forskolin and KCl-stimulated pathways. The results indicate that GABAB receptors negatively regulate cyclic AMP-responsive element binding protein-mediated transcription in the CNS.
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PMID:GABAB receptors negatively regulate transcription in cerebellar granular neurons through cyclic AMP responsive element binding protein-dependent mechanisms. 884 50

In previous studies, we have demonstrated that chronic administration of morphine or cocaine produces some common biochemical adaptations in the ventral tegmental area (VTA) and nucleus accumbens (NAc), components of the mesolimbic dopamine system implicated in the reinforcing actions of these and other drugs of abuse. Since this neural pathway is also implicated in the reinforcing actions of ethanol, it was of interest to determine whether chronic ethanol exposure results in similar biochemical adaptations. Indeed, as seen for chronic morphine and cocaine treatments, we show here that chronic ethanol treatment increased levels of tyrosine hydroxylase and glial fibrillary acidic protein immunoreactivity, and decreases levels of neurofilament protein immunoreactivity, in the VTA. Also like morphine and cocaine, ethanol increases levels of cyclic AMP-dependent protein kinase activity in the NAc. These actions of ethanol required long-term exposure to the drug, and were in most cases not seen in the substantia nigra or caudateputamen, components of the nigrostriatal dopamine system studied for comparison. Altered levels of tyrosine hydroxylase in catecholaminergic cells frequently reflect altered states of activation of the cells. Moreover, increasing evidence indicates that ethanol produces many of its acute effects on the brain by regulating NMDA glutamate and GABAA receptors. We therefore examined the influence of chronic ethanol treatment on levels of expression of specific glutamate and GABA receptor subunits in the VTA. It was found that long-term, but not short-term, ethanol exposure increased levels of immunoreactivity of the NMDAR1 subunit, an obligatory component of NMDA glutamate receptors, and of the GluR1 subunit, a component of many AMPA glutamate receptors; but at the same time, long-term ethanol exposure decreased immunoreactivity levels of the alpha 1 subunit of the GABAA receptor complex. These changes are consistent with an increased state of activation of VTA neurons inferred from the observed increase in tyrosine hydroxylase (TH) expression. These results demonstrate that chronic ethanol exposure results in several biochemical adaptations in the mesolimbic dopamine system, which may underlie prominent changes in the structural and functional properties of this neural pathway related to alcohol abuse and alcoholism.
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PMID:Biochemical actions of chronic ethanol exposure in the mesolimbic dopamine system. 886 59

Single electrode whole cell current- and voltage-clamp techniques in conjunction with intra- and extracellular phoresis and extracellular application of pharmacological agents were applied to study neurons in deep layers of the brainstem of anesthetized, paralyzed and artificially ventilated cats. We compared slow rhythmic changes and stimulus-evoked postsynaptic current and voltage responses of neurons as they were recorded with fine-tipped microelectrodes filled with 2-3 M 'microelectrode solutions' or with 0.3 M 'patch solutions', or with patch electrodes. The experimental data were then compared with the effects of somatic and dendritic conductance changes simulated in a cell model. A new method was introduced for alternating current and voltage-clamp measurements performed at 300 Hz, which provided quasi-simultaneous measurements of slow changes of spontaneous synaptic currents and potentials. During current or voltage clamp, chemicals which affect voltage- and receptor-controlled conductances were ionophoresed intracellularly through single or theta-type glass electrodes. We show examples of activation of low-voltage activated Ca2+ responses after blockade of Na+ currents by intracellular QX 314 and K+ currents by intracellular Cs+ injections in addition to Sp-cAMPs to activate protein kinase A. TEA, NMDA and GABA were used to demonstrate the effectiveness of extracellular application of drugs through multibarrel electrodes or local application through a 'bath'. The various tests demonstrated that single electrode whole cell current- and voltage-clamp methods, in combination with various techniques for drug application, can be well applied to study the biophysical properties and pharmacological sensitivities of neurons embedded in in vivo networks within deep layers of the brain.
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PMID:Voltage-clamp analysis of neurons within deep layers of the brain. 887 77

Norepinephrine and the beta-adrenergic receptor agonist, isoproterenol, have been shown to potentiate the amplitude of GABAA receptor-mediated whole-cell current responses in Purkinje cells acutely dissociated from the rat cerebellum. However, the steps leading from the activation of beta-adrenergic receptors to the modulation of GABAA receptor remain to be delineated. This study tested the hypothesis that a sequelae of intracellular intermediaries involving the cyclic AMP second messenger system serves as the subcellular link to promote this heteroreceptor interaction. Exposure to cholera toxin, but not to pertussis toxin, increased the amplitude of GABA-activated current responses in acutely dissociated Purkinje cells. Intracellular dialysis with guanosine 5'-O-(3-thiotriphosphate) also resulted in a time- and dose-dependent augmentation of the response to GABA. while guanosine 5'-O-(2-thiodiphosphate) blocked the norepinephrine-mediated facilitation. A positive modulation of the current response to GABA was observed following intracellular delivery of cyclic AMP or the catalytic subunit of the cyclic AMP-dependent protein kinase. Furthermore, the norepinephrine-induced potentiation of the GABA-activated current response was prevented in the presence of the Rp isomer of cyclic AMP, the regulatory subunit of cyclic AMP-dependent protein kinase and an inhibitor of cyclic AMP-dependent protein kinase. These findings led to the formulation of a working model in which activation of the beta-adrenergic receptor triggers a Gs-protein-mediated transduction cascade in cerebellar Purkinje cells which activates adenylate cyclase, resulting in a rise in intracellular levels of cyclic AMP, increased phosphorylating activity by cyclic AMP-dependent protein kinase and, ultimately, a potentiation of GABAA receptor function.
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PMID:Noradrenergic potentiation of cerebellar Purkinje cell responses to GABA: cyclic AMP as intracellular intermediary. 888 79

1. The effects of activation of endogenous adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA), intracellular application of PKA and inhibition of endogenous PKA by protein kinase inhibitory peptide (PKIP) on hippocampal dentate granule cell gamma-aminobuturic acid A (GABAA) receptor (GABAR) currents were characterized. 2. GABAR currents evoked by repeated application of GABA (30 or 100 microM) were enhanced by application of 1 mM norepinephrine (52 +/- 26%; mean +/- SE; n = 11) and of 500 mM 8-bromo cAMP (15 +/- 2%, n = 7). 3. GABA concentration response curves were obtained from six dentate granule cells before and after application of 500 microM 8-bromo cAMP. The maximal current was increased significantly by 89 +/- 36%, but the mean EC50 was not significantly changed (68 +/- 42 microM vs. 25 +/- 10 microM). 4. The GABA concentration response relationship was studied in a group of 7 granule cells recorded with pipettes containing PKIP and 2 mM ATP and compared with another group of 12 cells recorded with 2 mM ATP in the pipette. When currents were recorded with intracellular PKIP, the mean EC50 for GABA was no different (43 +/- 9 microM vs. 45 +/- 16 microM); however, the maximal current obtained was smaller, (961 +/- 102 pA vs. 658 +/- 104 pA). 5. Concentration response data were obtained from four granule cells using recording pipettes containing the cPKA and an ATP regeneration system and compared with seven cells recorded with the ATP regeneration system. With cPKA, the maximal GABAR current was significantly larger (1,224 +/- 132 pA vs. 718 +/- 56 pA), but the EC50 for GABA was not significantly altered (21 +/- 2.0 microM vs. 79 +/- 25 microM).
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PMID:Cyclic AMP-dependent protein kinase enhances hippocampal dentate granule cell GABAA receptor currents. 889 33


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