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Direct Pore Binding as a Mechanism for Isoflurane Inhibition of the Pentameric Ligand-gated Ion Channel ELIC.

Chen Q, Kinde MN, Arjunan P, Wells MM, Cohen AE, Xu Y, Tang P - Sci Rep (2015)

Bottom Line: Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition.Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation.This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15260, USA.

ABSTRACT
Pentameric ligand-gated ion channels (pLGICs) are targets of general anesthetics, but molecular mechanisms underlying anesthetic action remain debatable. We found that ELIC, a pLGIC from Erwinia chrysanthemi, can be functionally inhibited by isoflurane and other anesthetics. Structures of ELIC co-crystallized with isoflurane in the absence or presence of an agonist revealed double isoflurane occupancies inside the pore near T237(6') and A244(13'). A pore-radius contraction near the extracellular entrance was observed upon isoflurane binding. Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition. Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation. This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

No MeSH data available.


Related in: MedlinePlus

Inhibition of ELIC by general anesthetics.(a) Representative ELIC current traces elicited by propylamine (PPA) at EC20 in the absence and presence of the general anesthetics isoflurane (ISF, 50 μM), sevoflurane (SVF, 60 μM), halothane (HAL, 82 μM), propofol (PFL, 30 μM), etomidate (ETM, 30 μM), or thiopental (THP, 100 μM). The scale bars are 0.2 μA (vertical) and 30s (horizontal). The data were normalized to the current at EC20 in the absence of anesthetics and fit to the Hill equation (solid lines, n ≥ 6) for the volatile (b) and intravenous (c) general anesthetics. The best-fit parameters for both (b,c) are provided in Supplementary Table 1. The data are reported as the mean ± SEM and error bars less than the symbol size are not visible.
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f1: Inhibition of ELIC by general anesthetics.(a) Representative ELIC current traces elicited by propylamine (PPA) at EC20 in the absence and presence of the general anesthetics isoflurane (ISF, 50 μM), sevoflurane (SVF, 60 μM), halothane (HAL, 82 μM), propofol (PFL, 30 μM), etomidate (ETM, 30 μM), or thiopental (THP, 100 μM). The scale bars are 0.2 μA (vertical) and 30s (horizontal). The data were normalized to the current at EC20 in the absence of anesthetics and fit to the Hill equation (solid lines, n ≥ 6) for the volatile (b) and intravenous (c) general anesthetics. The best-fit parameters for both (b,c) are provided in Supplementary Table 1. The data are reported as the mean ± SEM and error bars less than the symbol size are not visible.

Mentions: As a homolog to eukaryotic pLGICs, ELIC shares similar pharmacological profiles of eukaryotic cation-conducting pLGICs with respect to modulation by general anesthetics. Both volatile and intravenous anesthetics inhibited ELIC in a concentration dependent manner (Fig. 1). At the agonist propylamine (PPA) concentration eliciting 20% of the maximal current (EC20), isoflurane, sevoflurane, and halothane produced 50% inhibition (IC50) at concentrations of 21.9 ± 1.5, 23.2 ± 1.6, and 40.0 ± 4.5 μM, respectively (Fig. 1b and Supplementary Table 1). The intravenous anesthetics propofol, etomidate and thiopental inhibited ELIC with IC50 of 11.9 ± 1.1, 11.2 ± 1.1 and 42.8 ± 1.1 μM, respectively (Fig. 1c and Supplementary Table 1). These results are comparable to the corresponding IC50 values observed on neuronal nAChRs31323435363738 (Supplementary Table 1), suggesting that ELIC is a suitable model for understanding anesthetic actions on pLGICs.


Direct Pore Binding as a Mechanism for Isoflurane Inhibition of the Pentameric Ligand-gated Ion Channel ELIC.

Chen Q, Kinde MN, Arjunan P, Wells MM, Cohen AE, Xu Y, Tang P - Sci Rep (2015)

Inhibition of ELIC by general anesthetics.(a) Representative ELIC current traces elicited by propylamine (PPA) at EC20 in the absence and presence of the general anesthetics isoflurane (ISF, 50 μM), sevoflurane (SVF, 60 μM), halothane (HAL, 82 μM), propofol (PFL, 30 μM), etomidate (ETM, 30 μM), or thiopental (THP, 100 μM). The scale bars are 0.2 μA (vertical) and 30s (horizontal). The data were normalized to the current at EC20 in the absence of anesthetics and fit to the Hill equation (solid lines, n ≥ 6) for the volatile (b) and intravenous (c) general anesthetics. The best-fit parameters for both (b,c) are provided in Supplementary Table 1. The data are reported as the mean ± SEM and error bars less than the symbol size are not visible.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561908&req=5

f1: Inhibition of ELIC by general anesthetics.(a) Representative ELIC current traces elicited by propylamine (PPA) at EC20 in the absence and presence of the general anesthetics isoflurane (ISF, 50 μM), sevoflurane (SVF, 60 μM), halothane (HAL, 82 μM), propofol (PFL, 30 μM), etomidate (ETM, 30 μM), or thiopental (THP, 100 μM). The scale bars are 0.2 μA (vertical) and 30s (horizontal). The data were normalized to the current at EC20 in the absence of anesthetics and fit to the Hill equation (solid lines, n ≥ 6) for the volatile (b) and intravenous (c) general anesthetics. The best-fit parameters for both (b,c) are provided in Supplementary Table 1. The data are reported as the mean ± SEM and error bars less than the symbol size are not visible.
Mentions: As a homolog to eukaryotic pLGICs, ELIC shares similar pharmacological profiles of eukaryotic cation-conducting pLGICs with respect to modulation by general anesthetics. Both volatile and intravenous anesthetics inhibited ELIC in a concentration dependent manner (Fig. 1). At the agonist propylamine (PPA) concentration eliciting 20% of the maximal current (EC20), isoflurane, sevoflurane, and halothane produced 50% inhibition (IC50) at concentrations of 21.9 ± 1.5, 23.2 ± 1.6, and 40.0 ± 4.5 μM, respectively (Fig. 1b and Supplementary Table 1). The intravenous anesthetics propofol, etomidate and thiopental inhibited ELIC with IC50 of 11.9 ± 1.1, 11.2 ± 1.1 and 42.8 ± 1.1 μM, respectively (Fig. 1c and Supplementary Table 1). These results are comparable to the corresponding IC50 values observed on neuronal nAChRs31323435363738 (Supplementary Table 1), suggesting that ELIC is a suitable model for understanding anesthetic actions on pLGICs.

Bottom Line: Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition.Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation.This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15260, USA.

ABSTRACT
Pentameric ligand-gated ion channels (pLGICs) are targets of general anesthetics, but molecular mechanisms underlying anesthetic action remain debatable. We found that ELIC, a pLGIC from Erwinia chrysanthemi, can be functionally inhibited by isoflurane and other anesthetics. Structures of ELIC co-crystallized with isoflurane in the absence or presence of an agonist revealed double isoflurane occupancies inside the pore near T237(6') and A244(13'). A pore-radius contraction near the extracellular entrance was observed upon isoflurane binding. Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition. Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation. This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

No MeSH data available.


Related in: MedlinePlus