scholarly journals Natural Product Isoliquiritigenin Activates GABAB Receptors to Decrease Voltage-Gate Ca2+ Channels and Glutamate Release in Rat Cerebrocortical Nerve Terminals

Biomolecules ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1537
Author(s):  
Tzu-Yu Lin ◽  
Cheng-Wei Lu ◽  
Pei-Wen Hsieh ◽  
Kuan-Ming Chiu ◽  
Ming-Yi Lee ◽  
...  
Keyword(s):  
Gabab Receptor ◽  
Glutamate Release ◽  
Receptor Activation ◽  
Gabab Receptors ◽  
Nerve Terminals ◽  
Type B ◽  
Kinase C ◽  
Acid Type ◽  
Dependent Inhibition ◽  
Ca2 Channels

Reduction in glutamate release is a key mechanism for neuroprotection and we investigated the effect of isoliquiritigenin (ISL), an active ingredient of Glycyrrhiza with neuroprotective activities, on glutamate release in rat cerebrocortical nerve terminals (synaptosomes). ISL produced a concentration-dependent inhibition of glutamate release and reduced the intraterminal [Ca2+] increase. The inhibition of glutamate release by ISL was prevented after removing extracellular Ca2+ or blocking P/Q-type Ca2+ channels. This inhibition was mediated through the γ-aminobutyric acid type B (GABAB) receptors because ISL was unable to inhibit glutamate release in the presence of baclofen (an GABAB agonist) or CGP3548 (an GABAB antagonist) and docking data revealed that ISL interacted with GABAB receptors. Furthermore, the ISL inhibition of glutamate release was abolished through the inhibition of Gi/o-mediated responses or Gβγ subunits, but not by 8-bromoadenosine 3′, 5′-cyclic monophosphate or adenylate cyclase inhibition. The ISL inhibition of glutamate release was also abolished through the inhibition of protein kinase C (PKC), and ISL decreased the phosphorylation of PKC. Thus, we inferred that ISL, through GABAB receptor activation and Gβγ-coupled inhibition of P/Q-type Ca2+ channels, suppressed the PKC phosphorylation to cause a decrease in evoked glutamate release at rat cerebrocortical nerve terminals.

Effects of Intravenous Anesthetic Agents on Glutamate Release

2000 ◽  
Vol 92 (4) ◽  
pp. 1067-1073 ◽  
Author(s):  
Donal J. Buggy ◽  
Beverley Nicol ◽  
David J. Rowbotham ◽  
David G. Lambert
Keyword(s):  
Glutamate Release ◽  
Receptor Activation ◽  
Gamma Aminobutyric Acid ◽  
Half Maximum ◽  
Intravenous Anesthetic ◽  
Anesthetic Agents ◽  
Acid Type ◽  
Maximum Inhibition ◽  
Dependent Inhibition ◽  
Anesthetic Action

Background Many anesthetic agents are known to enhance the alpha1beta2gamma2S gamma-aminobutyric acid type A (GABAA) chloride current; however, they also depress excitatory neurotransmission. The authors evaluated two hypotheses: intravenous anesthetic agents inhibit glutamate release and any observed inhibition may be secondary to GABAA receptor activation. Methods Cerebrocortical slices were prepared from Wistar rats. After perfusion in oxygenated Krebs buffer for 60 min at 37 degrees C, samples for glutamate assay were obtained at 2-nmin intervals. After 6 min, a 2-min pulse of 46 mM K+ was applied to the slices (S1); this was repeated after 30 min (S2). Bicuculline (1-100 microM) was applied when the S1 response returned to basal level, and 10 min later, thiopental (1-300 micro/M), propofol (10 microM), or ketamine (30 microM) were also applied until the end of S2. Perfusate glutamate concentrations were measured fluorometrically, and the area under the glutamate release curves was expressed as a ratio (S2/S1). Results Potassium (46 mM) evoked a monophasic release of glutamate during S1 and S2, with a mean control S2/S1 ratio of 1.07 +/- 0.33 (mean +/- SD, n = 96). Ketamine and thiopental produced a concentration-dependent inhibition of K+-evoked glutamate release with half-maximum inhibition of release values of 18.2 and 10.9 /microM, respectively. Release was also inhibited by propofol. Bicuculline produced a concentration dependent reversal of thiopental inhibition of glutamate release with a half-maximum reversal of the agonist effect of 10.3 microM. Bicuculline also reversed the effects of propofol but not those of ketamine. Conclusions The authors' data indicate that thiopental, propofol, and ketamine inhibit K+-evoked glutamate release from rat cerebrocortical slices. The inhibition produced by thiopental and propofol is mediated by activation of GABAA receptors, revealing a subtle interplay between GABA-releasing (GABAergic) and glutamatergic transmission in anesthetic action.

Synthesis and Pharmacological Evaluation of Novel γ-Aminobutyric Acid Type B (GABAB) Receptor Agonists as Gastroesophageal Reflux Inhibitors

2008 ◽  
Vol 51 (14) ◽  
pp. 4315-4320 ◽  
Author(s):  
Christer Alstermark ◽  
Kosrat Amin ◽  
Sean R. Dinn ◽  
Thomas Elebring ◽  
Ola Fjellström ◽  
...  
Keyword(s):  
Gastroesophageal Reflux ◽  
Gabab Receptor ◽  
Aminobutyric Acid ◽  
Type B ◽  
Receptor Agonists ◽  
Pharmacological Evaluation ◽  
Acid Type

Calcium Waves and Closure of Potassium Channels in Response to GABA Stimulation in Hermissenda Type B Photoreceptors

2002 ◽  
Vol 87 (2) ◽  
pp. 776-792 ◽  
Author(s):  
K. T. Blackwell
Keyword(s):  
Calcium Current ◽  
Calcium Concentration ◽  
Calcium Release ◽  
Input Resistance ◽  
Receptor Activation ◽  
Memory Storage ◽  
Type B ◽  
Kinase C ◽  
Hyperpolarization Activated Current ◽  
Receptor Channel

Classical conditioning of Hermissenda crassicornisrequires the paired presentation of a conditioned stimulus (light) and an unconditioned stimulus (turbulence). Light stimulation of photoreceptors leads to production of diacylglycerol, an activator of protein kinase C, and inositol triphosphate (IP3), which releases calcium from intracellular stores. Turbulence causes hair cells to release GABA onto the terminal branches of the type B photoreceptor. One prior study has shown that GABA stimulation produces a wave of calcium that propagates from the terminal branches to the soma and raises the possibility that two sources of calcium are required for memory storage. GABA stimulation also causes an inhibitory postsynaptic potential (IPSP) followed by a late depolarization and increase in input resistance, whose cause has not been identified. A model was developed of the effect of GABA stimulation on the Hermissenda type B photoreceptor to evaluate the currents underlying the late depolarization and to evaluate whether a calcium wave could propagate from the terminal branches to the soma. The model included GABAA, GABAB, and calcium-sensitive potassium leak channels; calcium dynamics including release of calcium from intracellular stores; and the biochemical reactions leading from GABAB receptor activation to IP3 production. Simulations show that it is possible for a wave of calcium to propagate from the terminal branches to the soma. The wave is initiated by IP3-induced calcium release but propagation requires release through the ryanodine receptor channel where IP3 concentration is small. Wave speed is proportional to peak calcium concentration at the crest of the wave, with a minimum speed of 9 μm/s in the absence of IP3. Propagation ceases when peak concentration drops below 1.2 μM; this occurs if the rate of calcium pumping into the endoplasmic reticulum is too large. Simulations also show that both a late depolarization and an increase in input resistance occur after GABA stimulation. The duration of the late depolarization corresponds to the duration of potassium leak channel closure. Neither the late depolarization nor the increase in input resistance are observed when a transient calcium current and a hyperpolarization-activated current are added to the model as replacement for closure of potassium leak channels. Thus the late depolarization and input resistance elevation can be explained by a closure of calcium-sensitive leak potassium currents but cannot be explained by a transient calcium current and a hyperpolarization-activated current.

Evaluation of Difluoromethyl Ketones as Agonists of the γ-Aminobutyric Acid Type B (GABAB) Receptor

2013 ◽  
Vol 56 (6) ◽  
pp. 2456-2465 ◽  
Author(s):  
Changho Han ◽  
Amy E. Salyer ◽  
Eun Hoo Kim ◽  
Xinyi Jiang ◽  
Rachel E. Jarrard ◽  
...  
Keyword(s):  
Gabab Receptor ◽  
Aminobutyric Acid ◽  
Type B ◽  
Acid Type

scholarly journals Presynaptic GABAB Receptors Regulate Retinohypothalamic Tract Synaptic Transmission by Inhibiting Voltage-Gated Ca2+ Channels

2006 ◽  
Vol 95 (6) ◽  
pp. 3727-3741 ◽  
Author(s):  
Mykhaylo G. Moldavan ◽  
Robert P. Irwin ◽  
Charles N. Allen
Keyword(s):  
Glutamate Release ◽  
Receptor Activation ◽  
Gabab Receptors ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Epsc Amplitude ◽  
Receptor Modulation ◽  
Joint Application ◽  
Retinohypothalamic Tract

Presynaptic GABAB receptor activation inhibits glutamate release from retinohypothalamic tract (RHT) terminals in the suprachiasmatic nucleus (SCN). Voltage-clamp whole cell recordings from rat SCN neurons and optical recordings of Ca2+-sensitive fluorescent probes within RHT terminals were used to examine GABAB-receptor modulation of RHT transmission. Baclofen inhibited evoked excitatory postsynaptic currents (EPSCs) in a concentration-dependent manner equally during the day and night. Blockers of N-, P/Q-, T-, and R-type voltage-dependent Ca2+ channels, but not L-type, reduced the EPSC amplitude by 66, 36, 32, and 18% of control, respectively. Joint application of multiple Ca2+ channel blockers inhibited the EPSCs less than that predicted, consistent with a model in which multiple Ca2+ channels overlap in the regulation of transmitter release. Presynaptic inhibition of EPSCs by baclofen was occluded by ω-conotoxin GVIA (≤72%), mibefradil (≤52%), and ω-agatoxin TK (≤15%), but not by SNX-482 or nimodipine. Baclofen reduced both evoked presynaptic Ca2+ influx and resting Ca2+ concentration in RHT terminals. Tertiapin did not alter the evoked EPSC and baclofen-induced inhibition, indicating that baclofen does not inhibit glutamate release by activation of Kir3 channels. Neither Ba2+ nor high extracellular K+ modified the baclofen-induced inhibition. 4-Aminopyridine (4-AP) significantly increased the EPSC amplitude and the charge transfer, and dramatically reduced the baclofen effect. These data indicate that baclofen inhibits glutamate release from RHT terminals by blocking N-, T-, and P/Q-type Ca2+ channels, and possibly by activation of 4-AP–sensitive K+ channels, but not by inhibition of R- and L-type Ca2+ channels or by Kir3 channel activation.

Potentiation of mGlu7 receptor-mediated glutamate release at nerve terminals containing N and P/Q type Ca2+ channels

2013 ◽  
Vol 67 ◽  
pp. 213-222 ◽  
Author(s):  
José Javier Ferrero ◽  
David Bartolomé-Martín ◽  
Magdalena Torres ◽  
José Sánchez-Prieto
Keyword(s):  
Glutamate Release ◽  
Nerve Terminals ◽  
Ca2 Channels

scholarly journals GABAB receptors in GtoPdb v.2021.2

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Bernhard Bettler ◽  
Norman G. Bowery ◽  
John F. Cryan ◽  
Sam J. Enna ◽  
David H. Farb ◽  
...  
Keyword(s):  
Transcription Initiation ◽  
Gabab Receptor ◽  
Recombinant Expression ◽  
Glutamate Release ◽  
Effector Proteins ◽  
Active State ◽  
Adult Brain ◽  
Gabab Receptors ◽  
Allosteric Modulator ◽  
Positive Allosteric Modulator

Functional GABAB receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on GABAB receptors [11, 71]) are formed from the heterodimerization of two similar 7TM subunits termed GABAB1 and GABAB2 [11, 70, 28, 71, 87]. GABAB receptors are widespread in the CNS and regulate both pre- and postsynaptic activity. The GABAB1 subunit, when expressed alone, binds both antagonists and agonists, but the affinity of the latter is generally 10-100-fold less than for the native receptor. Co-expression of GABAB1 and GABAB2 subunits allows transport of GABAB1 to the cell surface and generates a functional receptor that can couple to signal transduction pathways such as high-voltage-activated Ca2+ channels (Cav2.1, Cav2.2), or inwardly rectifying potassium channels (Kir3) [12, 11, 5]. The GABAB1 subunit harbours the GABA (orthosteric)-binding site within an extracellular domain (ECD) venus flytrap module (VTM), whereas the GABAB2 subunit mediates G protein-coupled signalling [11, 70, 40, 39]. The cryo-electron microscopy structures of the human full-length GABAB1-GABAB2 heterodimer have been solved in the inactive apo state, two intermediate agonist-bound forms and an active state in which the heterodimer is bound to an agonist and a positive allosteric modulator [81]. The positive allosteric modulator binds to the transmembrane dimerization interface and stabilizes the active state. Recent evidence indicates that higher order assemblies of GABAB receptor comprising dimers of heterodimers occur in recombinant expression systems and in vivo and that such complexes exhibit negative functional cooperativity between heterodimers [69, 22]. Adding further complexity, KCTD (potassium channel tetramerization proteins) 8, 12, 12b and 16 associate as tetramers with the carboxy terminus of the GABAB2 subunit to impart altered signalling kinetics and agonist potency to the receptor complex [86, 3, 79] and are reviewed by [72]. The molecular complexity of GABAB receptors is further increased through association with trafficking and effector proteins [80] and reviewed by [68]. The predominant GABAB1a and GABAB1b isoforms, which are most prevalent in neonatal and adult brain tissue respectively, differ in their ECD sequences as a result of the use of alternative transcription initiation sites. GABAB1a-containing heterodimers localise to distal axons and mediate inhibition of glutamate release in the CA3-CA1 terminals, and GABA release onto the layer 5 pyramidal neurons, whereas GABAB1b-containing receptors occur within dendritic spines and mediate slow postsynaptic inhibition [74, 91]. Amyloid precursor protein (APP) and soluble APP (sAPP) bind to the N- terminal sushi domain of the GABAB1a isoform to regulate axonal trafficking of GABAB receptors and release of neurotransmitters [76].

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