The Sensitivity of G Protein-activated K+ Channels toward Halothane Is Essentially Determined by the C Terminus

Milovic, Sergej; Steinecker-Frohnwieser, Bibiane; Schultze-Seemann, Wolfgang; Weigl, Lukas

doi:10.1074/jbc.m403448200

Cited by 22 publications

(21 citation statements)

References 34 publications

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“…This site at the helix bundle crossing in the transmembrane domain of the channel comprises the G␤␥-operated gate (50); hence, halothane binding to the aromatic residue here could control gating. This amino acid residue is contained within the larger regions identified in previous studies that affected halothane sensitivity (11,28). Consistent with those reports, our findings suggest that the agonist-mediated currents are most highly sensitive to the effects of halothane.…”

Section: Discussionsupporting

confidence: 81%

“…Therefore, in Kir3.2 channels, G␤␥ activation may be stronger, and halothane is a less efficacious partial agonist, leading to the largest inhibition. A previous study (28) found that halothane has different effects on Kir3.1 at low and high concentrations. Our model explains those findings where the activation of halothane as a partial agonist would only be manifested at high concentrations because G␤␥ activation of homomeric Kir3.1 may not be as efficacious as those for other subtypes, especially under basal conditions tested in that study (28).…”

Section: Discussionmentioning

confidence: 99%

“…Small replacements in the pore and TM2 region showed that the pore and the first half of the TM2 are not involved in halothane sensitivity. Another study showed that deletion of a large portion of the Kir3.2 C terminus removed the effect of halothane (28). Biochemically, they showed that volatile anesthetics did not change G␤␥ binding to the channel C terminus in GST pulldown assays.…”

Section: Mutants That Impair G␤␥ Interaction With the Channelmentioning

confidence: 99%

“…5A). (28) showed that Kir3.1(F137S), a homomeric active mutant channel (46), is activated by high concentrations of halothane (1 mM), whereas it is inhibited by low concentrations of halothane (100 M). In light of these findings, we performed halothane dose-response curves for channels harboring the L273I or F192M mutation.…”

Section: Mutants That Impair G␤␥ Interaction With the Channelmentioning

confidence: 99%

“…Although like all other inward rectifiers, Kir3 channels require the membrane phospholipid phosphatidylinositol 4,5-bisphosphate for their activity (25,26), they have weak phosphatidylinositol 4,5-bisphosphate interactions (27). Previous studies have identified regions in the C terminus (28) and the transmembrane domain (11) that contribute to halothane sensitivity but did not identify specific molecular correlates for the effect of halothane. Given the critical role of Kir3 channels in neurotransmission, we set out to determine the mechanistic basis for their paradoxical inhibition by halothane.…”

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confidence: 99%

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G Protein βγ Gating Confers Volatile Anesthetic Inhibition to Kir3 Channels

Styer

Mirshahi

Wang

et al. 2010

Journal of Biological Chemistry

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G protein-activated inwardly rectifying potassium (GIRK or Kir3) channels are directly gated by the ␤␥ subunits of G proteins and contribute to inhibitory neurotransmitter signaling pathways. Paradoxically, volatile anesthetics such as halothane inhibit these channels. We find that neuronal Kir3 currents are highly sensitive to inhibition by halothane. Given that Kir3 currents result from increased G␤␥ available to the channels, we asked whether reducing available G␤␥ to the channel would adversely affect halothane inhibition. Remarkably, scavenging G␤␥ using the C-terminal domain of ␤-adrenergic receptor kinase (c␤ARK) resulted in channel activation by halothane. Consistent with this effect, channel mutants that impair G␤␥ activation were also activated by halothane. A single residue, phenylalanine 192, occupies the putative G␤␥ gate of neuronal Kir3.2 channels. Mutation of Phe-192 at the gate to other residues rendered the channel non-responsive, either activated or inhibited by halothane. These data indicated that halothane predominantly interferes with G␤␥-mediated Kir3 currents, such as those functioning during inhibitory synaptic activity. Our report identifies the molecular correlate for anesthetic inhibition of Kir3 channels and highlights the significance of these effects in modulating neurotransmitter-mediated inhibitory signaling.Ion channels that control the excitability of neuronal conduction pathways are important targets for halogenated volatile anesthetics (HVAs) 4 (1, 2). HVAs such as halothane enhance the activity of inhibitory GABA A and glycine receptors and inhibit excitatory channels such as glutamate and nicotinic receptors (3). Several two-pore domain K (K 2 P) channels are activated by HVAs (4 -6). G protein-activated inwardly rectifying potassium (GIRK or Kir3) channels are also involved in inhibitory neurotransmission (7). Although ethanol and chloroform activate Kir3 channels (8, 9), paradoxically HVAs inhibit Kir3 channels (10, 11). Therefore, Kir3 channels present a rare case where an HVA such as halothane impairs inhibitory signaling by an ion channel.The exact mechanism for modulation of ion channels by volatile anesthetics is not fully clear (2). Two residues in the TM2 and TM3 of GABA A participate in regulating the effects of enflurane (12). In nicotinic receptors, sites of action for halothane on tyrosine residues near the channel pore were identified (13). The transmembrane domains in AMPA and NMDA receptors play critical roles in their anesthetics and ethanol sensitivity (14,15). Several sites on various K 2 P channels have been identified that are involved in anesthetic sensitivity (5, 16).Inhibitory neurotransmitters, exemplified by GABA, stimulate G␣ i/o -coupled receptors (17, 18) and liberate G␤␥ that directly activates Kir3 channels (19). Kir3 channels mediate slow inhibitory post-synaptic currents in central neurons, limiting neuronal excitability (7). Kir3-null mice show increased seizure susceptibility (20), hyperalgesia (21), and reduced neurotransmitter-, morphine...

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Section: Discussionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Mutants That Impair G␤␥ Interaction With the Channelmentioning

confidence: 99%

Section: Mutants That Impair G␤␥ Interaction With the Channelmentioning

confidence: 99%

mentioning

confidence: 99%

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G Protein βγ Gating Confers Volatile Anesthetic Inhibition to Kir3 Channels

Styer

Mirshahi

Wang

et al. 2010

Journal of Biological Chemistry

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The Un(f)told Story of General Anesthesia

Zsila

2018

ChemBioChem

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Inhalational anesthetics are routinely employed in clinical practice to accomplish general anesthesia. Concerns have recently emerged regarding the deleterious impact of these volatile agents on cognitive performance, immune functions, and tumor recurrence and metastasis. These agents have been shown to modify the gene-expression pattern as well as cell signaling in tumor cells, but the underlying molecular mechanisms remain a matter of conjecture. Regulatory/signaling proteins either of cytosolic or membrane origin abundantly contain intrinsically disordered sequences, the conformational pliability of which is pivotal in their biological functions. It is well known that chloroform (an anesthetic itself), trifluoroethanol, hexafluoroisopropanol, and related haloalcohols markedly affect the structure of disordered proteins and protein regions by inducing folding, misfolding, or even aggregation. Taking into consideration the physicochemical similarities and protein interaction modes of these volatile solvents and inhaled anesthetics, it is postulated that administration of these drugs can also modify the secondary structure of disordered protein segments. Accordingly, pharmacological effects of anesthetics may, at least in part, be mediated by conformational perturbations of intrinsic disorder-based regulatory protein networks of cells.

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Abnormal expression of the G‐protein‐activated inwardly rectifying potassium channel 2 (GIRK2) in hippocampus, frontal cortex, and substantia nigra of Ts65Dn mouse: A model of Down syndrome

Harashima

Jacobowitz

Witta

et al. 2005

J of Comparative Neurology

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Ts65Dn, a mouse model of Down syndrome (DS), demonstrates abnormal hippocampal synaptic plasticity and behavioral abnormalities related to spatial learning and memory. The molecular mechanisms leading to these impairments have not been identified. In this study, we focused on the G-protein-activated inwardly rectifying potassium channel 2 (GIRK2) gene that is highly expressed in the hippocampus region. We studied the expression pattern of GIRK subunits in Ts65Dn and found that GIRK2 was over-expressed in all analyzed Ts65Dn brain regions. Interestingly elevated levels of GIRK2 protein in the Ts65Dn hippocampus and frontal cortex correlated with elevated levels of GIRK1 protein. This suggests that heteromeric GIRK1-GIRK2 channels are over-expressed in Ts65Dn hippocampus and frontal cortex, which could impair excitatory input, modulate spike frequency and synaptic kinetics in the affected regions. All GIRK2 splicing isoforms examined were expressed at higher levels in the Ts65Dn in comparison to the diploid hippocampus. The pattern of GIRK2 expression in the Ts65Dn mouse brain revealed by in situ hybridization and immunohistochemistry was similar to that previously reported in the rodent brain. However, in the Ts65Dn mouse a strong immunofluorescent staining of GIRK2 was detected in the lacunosum molecular layer of the CA3 area of the hippocampus. In addition, tyrosine hydroxylase containing dopaminergic neurons that co-express GIRK2 were more numerous in the substantia nigra compacta and ventral tegmental area in the Ts65Dn compared to diploid controls. In summary, the regional localization and the increased brain levels coupled with known function of the GIRK channel may suggest an important contribution of GIRK2 containing channels to Ts65Dn and thus to DS neurophysiological phenotypes.

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The Sensitivity of G Protein-activated K+ Channels toward Halothane Is Essentially Determined by the C Terminus

Cited by 22 publications

References 34 publications

G Protein βγ Gating Confers Volatile Anesthetic Inhibition to Kir3 Channels

G Protein βγ Gating Confers Volatile Anesthetic Inhibition to Kir3 Channels

The Un(f)told Story of General Anesthesia

Abnormal expression of the G‐protein‐activated inwardly rectifying potassium channel 2 (GIRK2) in hippocampus, frontal cortex, and substantia nigra of Ts65Dn mouse: A model of Down syndrome

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