β3-Containing Gamma-Aminobutyric AcidA Receptors Are Not Major Targets for the Amnesic and Immobilizing Actions of Isoflurane

Liao, Mark; Sonner, James M.; Jurd, Rachel; Rudolph, Uwe; Borghese, Cecilia M.; Harris, R. Adron; Laster, Michael J.; Eger, Edmond I.

doi:10.1213/01.ane.0000154196.86587.35

Cited by 51 publications

(38 citation statements)

References 19 publications

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“…The gene KI approach has been used with great success to clearly define the role of the beta 2 and beta 3 subunits of the GABA A receptor with respect to propofol and etomidate anesthesia [8,17]. The beta 3 KI mice also suggest a minor role for this subunit in inhaled anesthetic action [8,12]. Our gene KI results with anesthetic insensitive alpha1 GABA A receptor gene KI also suggests that these receptors play little role in isoflurane MAC.…”

Section: Discussionmentioning

confidence: 66%

Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant γ-aminobutyric acid type-A receptors

Kim

Atherley

Werner

et al. 2007

Neuroscience Letters

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Anesthetics produce immobility and depress spinal nociceptive processing, but the exact sites and mechanisms of anesthetic action are unknown. The gamma-aminobutyric acid type-A (GABA A ) receptor is thought to be important to anesthetic action. We studied knockin mice that had mutations in the alpha1 subunit of the GABA A receptor that imparts resistance to isoflurane in in vitro systems. We determined the isoflurane minimum alveolar concentration (MAC) that produces immobility in 50% of subjects and responses of lumbar neurons (single-unit recordings) to noxious stimulation (5 s pinch) of the hindpaw. Isoflurane MAC did not differ between wildtype (1.1 ± 0.1%) and knock-in (1.1 ± 0.1%) mice. Isoflurane depressed neuronal responses to noxious stimulation (60 sec period during and after pinch) similarly in both wild-type and knockin mice (555 ± 133 and 636 ±106 impulses/min, respectively, at 0.8 MAC and 374 ± 81 and 409 ±85 impulses/min at 1.2 MAC). We conclude that isoflurane enhancement of alpha1 -containing GABA A receptors is not required to produce immobility or depress spinal nociceptive processing. KeywordsSpinal cord; GABA receptor; isoflurane; immobility; anesthesia Anesthetics are widely used but we still do not fully understand how these powerful and potentially unsafe drugs produce general anesthesia, which includes amnesia, unconsciousness and immobility. Analgesia and control of autonomic responses to noxious stimuli are also desirable components of general anesthesia [1]. Immobility is determined

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Section: Discussionmentioning

confidence: 66%

Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant γ-aminobutyric acid type-A receptors

Kim

Atherley

Werner

et al. 2007

Neuroscience Letters

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“…anesthetics (40,41), but this mechanism alone does not account for the lesser target selectivity of volatile anesthetics compared with i.v. anesthetics (42,43). Potential synaptic volatile anesthetic targets involved in regulating transmitter release include glutamate receptors, Na v channels (44), K 2P channels (45), nicotinic acetylcholine receptors (34), Ca v channels (46), neurotransmitter transporters (47,48), and SNARE proteins (8,49).…”

Section: Discussionmentioning

confidence: 99%

“…The depressive effects of isoflurane on hippocampal CA1 neuron excitability in rat brain slices involve primarily nonGABAergic mechanisms including direct depression of glutamate-mediated excitation (61), which supports an important role for effects on glutamatergic transmission. A nonGABAergic mechanism such as suppression of excitatory transmission through Na v channel blockade (42,43,62) is likely to mediate isofluraneinduced immobility, a ventral spinal anesthetic endpoint (63).…”

Section: Discussionmentioning

confidence: 99%

Isoflurane inhibits synaptic vesicle exocytosis through reduced Ca ²⁺ influx, not Ca ²⁺ -exocytosis coupling

Baumgart

Zhou

Hara

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

108

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Identifying presynaptic mechanisms of general anesthetics is critical to understanding their effects on synaptic transmission. We show that the volatile anesthetic isoflurane inhibits synaptic vesicle (SV) exocytosis at nerve terminals in dissociated rat hippocampal neurons through inhibition of presynaptic Ca 2+ influx without significantly altering the Ca 2+ sensitivity of SV exocytosis. A clinically relevant concentration of isoflurane (0.7 mM) inhibited changes in [Ca 2+ ] i driven by single action potentials (APs) by 25 ± 3%, which in turn led to 62 ± 3% inhibition of single AP-triggered exocytosis at 4 mM extracellular Ca 2+ ([Ca 2+ ] e ). Lowering external Ca 2+ to match the isoflurane-induced reduction in Ca 2+ entry led to an equivalent reduction in exocytosis. These data thus indicate that anesthetic inhibition of neurotransmitter release from small SVs occurs primarily through reduced axon terminal Ca 2+ entry without significant direct effects on Ca 2+ -exocytosis coupling or on the SV fusion machinery. Isoflurane inhibition of exocytosis and Ca 2+ influx was greater in glutamatergic compared with GABAergic nerve terminals, consistent with selective inhibition of excitatory synaptic transmission. Such alteration in the balance of excitatory to inhibitory transmission could mediate reduced neuronal interactions and network-selective effects observed in the anesthetized central nervous system. GCaMP3 | pHlourin | mechanisms of anesthesia | live cell imaging | presynaptic T he molecular and cellular mechanisms of anesthetic-induced amnesia, unconsciousness and immobilization are incompletely understood, particularly for the modern halogenated ether derivatives like isoflurane. General anesthetics, which are essential to both medical practice and experimental neuroscience, have potent and selective effects on neurotransmission (1), including both presynaptic actions (reduced neurotransmitter release) and postsynaptic actions (modulation of receptor function). These effects contribute to anesthetic-induced reductions in neuronal interactions, which are critical to information processing and consciousness (2-4). Knowledge of the fundamental synaptic effects of anesthetics is therefore essential to a molecular and physiological understanding of anesthetic mechanisms, and to development of more selective and safer anesthetics.Although postsynaptic electrophysiological effects of anesthetics can be assessed directly using whole cell recordings and heterologous expression of putative molecular targets, their presynaptic actions have been difficult to resolve by conventional approaches that do not clearly discriminate between presynaptic and postsynaptic contributions. Direct evidence for presynaptic effects of volatile anesthetics includes selective inhibition of glutamate release from isolated nerve terminals (5, 6) and of synaptic vesicle (SV) exocytosis in intact hippocampal neurons (7). However, it remains controversial whether these effects involve direct inhibition of SV exocytosis itself or of upstrea...

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“…Knock-in mice containing a ␤ 2 (N265S) mutation have been constructed and are resistant to the sedative effects of etomidate, but the effects of alcohols or volatile anesthetics have not been tested in these animals (Reynolds et al, 2003). In addition, ␤ 3 (N265M) mice have been constructed; however, this subunit does not seem to have a major role in the effects of ethanol or isoflurane (Liao et al, 2005;Sanchis-Segura et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

A Transmembrane Amino Acid in the GABA_A Receptor β₂ Subunit Critical for the Actions of Alcohols and Anesthetics

McCracken

Borghese

Trudell

et al. 2010

J Pharmacol Exp Ther

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Alcohols and inhaled anesthetics enhance the function of GABA A receptors containing ␣, ␤, and ␥ subunits. Molecular analysis has focused on the role of the ␣ subunits; however, there is evidence that the ␤ subunits may also be important. The goal of our study was to determine whether Asn265, which is homologous to the site implicated in the ␣ subunit (Ser270), contributes to an alcohol and volatile anesthetic binding site in the GABA A receptor ␤ 2 subunit. We substituted cysteine for Asn265 and exposed the mutant to the sulfhydryl-specific reagent octyl methanethiosulfonate (OMTS). We used two-electrode voltage-clamp electrophysiology in Xenopus laevis oocytes and found that, after OMTS application, GABA-induced currents were irreversibly potentiated in mutant ␣ 1 ␤ 2 (N265C)␥ 2S receptors [but not ␣ 1 ␤ 2 (I264C)␥ 2S ], presumably because of the covalent linking of octanethiol to the thiol group in the substituted cysteine. It is noteworthy that this effect was blocked when OMTS was applied in the presence of octanol. We found that potentiation by butanol, octanol, or isoflurane in the N265C mutant was nearly abolished after the application of OMTS, suggesting that an alcohol and volatile anesthetic binding site at position 265 of the ␤ 2 subunit was irreversibly occupied by octanethiol and consequently prevented butanol or isoflurane from binding and producing their effects. OMTS did not affect modulation or direct activation by pentobarbital, but there was a partial reduction of allosteric modulation by flunitrazepam and alphaxalone in mutant ␣ 1 ␤ 2 (N265C)␥ 2S receptors after OMTS was applied. Our findings provide evidence that Asn265 may contribute to an alcohol and anesthetic binding site.

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β3-Containing Gamma-Aminobutyric AcidA Receptors Are Not Major Targets for the Amnesic and Immobilizing Actions of Isoflurane

Abstract: The results of the present study indicate that beta3-containing gamma-aminobutyric acidA receptors do not mediate the amnesia produced by isoflurane and do not mediate, or only partially mediate, the immobility produced by inhaled anesthetics.

Cited by 51 publications

References 19 publications

Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant γ-aminobutyric acid type-A receptors

Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant γ-aminobutyric acid type-A receptors

Isoflurane inhibits synaptic vesicle exocytosis through reduced Ca ²⁺ influx, not Ca ²⁺ -exocytosis coupling

A Transmembrane Amino Acid in the GABA_A Receptor β₂ Subunit Critical for the Actions of Alcohols and Anesthetics

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β3-Containing Gamma-Aminobutyric AcidA Receptors Are Not Major Targets for the Amnesic and Immobilizing Actions of Isoflurane

Abstract: The results of the present study indicate that beta3-containing gamma-aminobutyric acidA receptors do not mediate the amnesia produced by isoflurane and do not mediate, or only partially mediate, the immobility produced by inhaled anesthetics.

Cited by 51 publications

References 19 publications

Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant γ-aminobutyric acid type-A receptors

Isoflurane depression of spinal nociceptive processing and minimum alveolar anesthetic concentration are not attenuated in mice expressing isoflurane resistant γ-aminobutyric acid type-A receptors

Isoflurane inhibits synaptic vesicle exocytosis through reduced Ca 2+ influx, not Ca 2+ -exocytosis coupling

A Transmembrane Amino Acid in the GABAA Receptor β2 Subunit Critical for the Actions of Alcohols and Anesthetics

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Isoflurane inhibits synaptic vesicle exocytosis through reduced Ca ²⁺ influx, not Ca ²⁺ -exocytosis coupling

A Transmembrane Amino Acid in the GABA_A Receptor β₂ Subunit Critical for the Actions of Alcohols and Anesthetics