Subunit-dependent interaction of the general anaesthetic etomidate with the γ-aminobutyric acid type A receptor

Claire Hill-Yenning, Delia Belelli, John A. Peters, Jeremy J. Lambert

Research output: Contribution to journalArticle

186 Citations (Scopus)

Abstract

1. The GABA modulating and GABA-mimetic actions of the general anaesthetic etomidate were examined in voltage-clamp recordings performed on Xenopus laevis oocytes induced, by cRNA injection, to express human recombinant γ-aminobutyric acid(A) (GABA(A)) receptor subunits. 2. Currents mediated by recombinant receptors with the ternary subunit composition α(x)β(y)γ(2L) (where x = 1,2,3 or 6 and y = 1 or 2), in response to GABA applied at the appropriate EC10, were enhanced by etomidate in a manner that was dependent upon the identity of both the α and β subunit isoforms. 3. For the β2-subunit containing receptors tested, the EC50 for the potentiation of GABA-evoked currents by etomidate (range 0.6 to 1.2 μM) was little affected by the nature of the α subunit present within the hetero-oligomeric complex. However, replacement of the β2 by the β1 subunit produced a 9-12 fold increase in the etomidate EC50 (6 to 11 μM) for all α-isoforms tested. 4. For α1, α2 and α6, but not α3-subunit containing receptors, the maximal potentiation of GABA-evoked currents by etomidate was greater for β2- than for β1-subunit containing receptors. This was most clearly exemplified by receptors composed of α6β1γ(2L) compared to α6β2γ(2L) subunits, where a maximally effective concentration of etomidate potentiated currents evoked by GABA at EC10 to 28 ± 2% and 169 ± 4% of the maximal GABA response, respectively. 5. For α1 subunit-containing receptors, the potency and maximal potentiating effect of either pentobarbitone or propofol was essentially unaffected by the β subunit isoform contained within the receptor complex. The potency of the anaesthetic neurosteroid 5α-pregnan-3α-ol-20-one was marginally higher for β1 rather than the β2 subunit-containing receptor, although its maximal effect was similar at the two receptor isoforms. 6. The GABA-mimetic action of etomidate was supported by β2- but not β1-subunit containing receptors, whereas that of pentobarbitone or propofol was evident with either β isoform. For β2-subunit containing receptors, both the agonist EC50 and the maximal current produced by etomidate were additionally influenced by the α isoform. 7. It is concluded that the subtype of β-subunit influences the potency with which etomidate potentiates GABA-evoked currents and that the β isoform is a crucial determinant of the GABA-mimetic activity of this compound. The nature of the α-subunit also impacts upon the maximal potentiation and activation that the compound may elicit. Such pronounced influences may aid the identification of the site that recognises etomidate. More generally, these results provide a clear example of structural specificity in anaesthetic action.

Original languageEnglish
Pages (from-to)749-756
Number of pages8
JournalBritish Journal of Pharmacology
Volume120
Issue number5
DOIs
Publication statusPublished - Feb 1997

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Etomidate
Aminobutyrates
General Anesthetics
gamma-Aminobutyric Acid
Protein Isoforms
Propofol
Pentobarbital
Anesthetics
Complementary RNA
Xenopus laevis
GABA-A Receptors
Oocytes
Neurotransmitter Agents

Keywords

  • 5α-pregnan-3α-ol-20-one
  • Etomidate
  • GABA(A) receptor
  • GABA(A) receptor α, β and γ subunits
  • Intravenous general anaesthetics
  • Pentobarbitone
  • Propofol

Cite this

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title = "Subunit-dependent interaction of the general anaesthetic etomidate with the γ-aminobutyric acid type A receptor",
abstract = "1. The GABA modulating and GABA-mimetic actions of the general anaesthetic etomidate were examined in voltage-clamp recordings performed on Xenopus laevis oocytes induced, by cRNA injection, to express human recombinant γ-aminobutyric acid(A) (GABA(A)) receptor subunits. 2. Currents mediated by recombinant receptors with the ternary subunit composition α(x)β(y)γ(2L) (where x = 1,2,3 or 6 and y = 1 or 2), in response to GABA applied at the appropriate EC10, were enhanced by etomidate in a manner that was dependent upon the identity of both the α and β subunit isoforms. 3. For the β2-subunit containing receptors tested, the EC50 for the potentiation of GABA-evoked currents by etomidate (range 0.6 to 1.2 μM) was little affected by the nature of the α subunit present within the hetero-oligomeric complex. However, replacement of the β2 by the β1 subunit produced a 9-12 fold increase in the etomidate EC50 (6 to 11 μM) for all α-isoforms tested. 4. For α1, α2 and α6, but not α3-subunit containing receptors, the maximal potentiation of GABA-evoked currents by etomidate was greater for β2- than for β1-subunit containing receptors. This was most clearly exemplified by receptors composed of α6β1γ(2L) compared to α6β2γ(2L) subunits, where a maximally effective concentration of etomidate potentiated currents evoked by GABA at EC10 to 28 ± 2{\%} and 169 ± 4{\%} of the maximal GABA response, respectively. 5. For α1 subunit-containing receptors, the potency and maximal potentiating effect of either pentobarbitone or propofol was essentially unaffected by the β subunit isoform contained within the receptor complex. The potency of the anaesthetic neurosteroid 5α-pregnan-3α-ol-20-one was marginally higher for β1 rather than the β2 subunit-containing receptor, although its maximal effect was similar at the two receptor isoforms. 6. The GABA-mimetic action of etomidate was supported by β2- but not β1-subunit containing receptors, whereas that of pentobarbitone or propofol was evident with either β isoform. For β2-subunit containing receptors, both the agonist EC50 and the maximal current produced by etomidate were additionally influenced by the α isoform. 7. It is concluded that the subtype of β-subunit influences the potency with which etomidate potentiates GABA-evoked currents and that the β isoform is a crucial determinant of the GABA-mimetic activity of this compound. The nature of the α-subunit also impacts upon the maximal potentiation and activation that the compound may elicit. Such pronounced influences may aid the identification of the site that recognises etomidate. More generally, these results provide a clear example of structural specificity in anaesthetic action.",
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author = "Claire Hill-Yenning and Delia Belelli and Peters, {John A.} and Lambert, {Jeremy J.}",
year = "1997",
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language = "English",
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pages = "749--756",
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Subunit-dependent interaction of the general anaesthetic etomidate with the γ-aminobutyric acid type A receptor. / Hill-Yenning, Claire; Belelli, Delia; Peters, John A.; Lambert, Jeremy J.

In: British Journal of Pharmacology, Vol. 120, No. 5, 02.1997, p. 749-756.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Subunit-dependent interaction of the general anaesthetic etomidate with the γ-aminobutyric acid type A receptor

AU - Hill-Yenning, Claire

AU - Belelli, Delia

AU - Peters, John A.

AU - Lambert, Jeremy J.

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N2 - 1. The GABA modulating and GABA-mimetic actions of the general anaesthetic etomidate were examined in voltage-clamp recordings performed on Xenopus laevis oocytes induced, by cRNA injection, to express human recombinant γ-aminobutyric acid(A) (GABA(A)) receptor subunits. 2. Currents mediated by recombinant receptors with the ternary subunit composition α(x)β(y)γ(2L) (where x = 1,2,3 or 6 and y = 1 or 2), in response to GABA applied at the appropriate EC10, were enhanced by etomidate in a manner that was dependent upon the identity of both the α and β subunit isoforms. 3. For the β2-subunit containing receptors tested, the EC50 for the potentiation of GABA-evoked currents by etomidate (range 0.6 to 1.2 μM) was little affected by the nature of the α subunit present within the hetero-oligomeric complex. However, replacement of the β2 by the β1 subunit produced a 9-12 fold increase in the etomidate EC50 (6 to 11 μM) for all α-isoforms tested. 4. For α1, α2 and α6, but not α3-subunit containing receptors, the maximal potentiation of GABA-evoked currents by etomidate was greater for β2- than for β1-subunit containing receptors. This was most clearly exemplified by receptors composed of α6β1γ(2L) compared to α6β2γ(2L) subunits, where a maximally effective concentration of etomidate potentiated currents evoked by GABA at EC10 to 28 ± 2% and 169 ± 4% of the maximal GABA response, respectively. 5. For α1 subunit-containing receptors, the potency and maximal potentiating effect of either pentobarbitone or propofol was essentially unaffected by the β subunit isoform contained within the receptor complex. The potency of the anaesthetic neurosteroid 5α-pregnan-3α-ol-20-one was marginally higher for β1 rather than the β2 subunit-containing receptor, although its maximal effect was similar at the two receptor isoforms. 6. The GABA-mimetic action of etomidate was supported by β2- but not β1-subunit containing receptors, whereas that of pentobarbitone or propofol was evident with either β isoform. For β2-subunit containing receptors, both the agonist EC50 and the maximal current produced by etomidate were additionally influenced by the α isoform. 7. It is concluded that the subtype of β-subunit influences the potency with which etomidate potentiates GABA-evoked currents and that the β isoform is a crucial determinant of the GABA-mimetic activity of this compound. The nature of the α-subunit also impacts upon the maximal potentiation and activation that the compound may elicit. Such pronounced influences may aid the identification of the site that recognises etomidate. More generally, these results provide a clear example of structural specificity in anaesthetic action.

AB - 1. The GABA modulating and GABA-mimetic actions of the general anaesthetic etomidate were examined in voltage-clamp recordings performed on Xenopus laevis oocytes induced, by cRNA injection, to express human recombinant γ-aminobutyric acid(A) (GABA(A)) receptor subunits. 2. Currents mediated by recombinant receptors with the ternary subunit composition α(x)β(y)γ(2L) (where x = 1,2,3 or 6 and y = 1 or 2), in response to GABA applied at the appropriate EC10, were enhanced by etomidate in a manner that was dependent upon the identity of both the α and β subunit isoforms. 3. For the β2-subunit containing receptors tested, the EC50 for the potentiation of GABA-evoked currents by etomidate (range 0.6 to 1.2 μM) was little affected by the nature of the α subunit present within the hetero-oligomeric complex. However, replacement of the β2 by the β1 subunit produced a 9-12 fold increase in the etomidate EC50 (6 to 11 μM) for all α-isoforms tested. 4. For α1, α2 and α6, but not α3-subunit containing receptors, the maximal potentiation of GABA-evoked currents by etomidate was greater for β2- than for β1-subunit containing receptors. This was most clearly exemplified by receptors composed of α6β1γ(2L) compared to α6β2γ(2L) subunits, where a maximally effective concentration of etomidate potentiated currents evoked by GABA at EC10 to 28 ± 2% and 169 ± 4% of the maximal GABA response, respectively. 5. For α1 subunit-containing receptors, the potency and maximal potentiating effect of either pentobarbitone or propofol was essentially unaffected by the β subunit isoform contained within the receptor complex. The potency of the anaesthetic neurosteroid 5α-pregnan-3α-ol-20-one was marginally higher for β1 rather than the β2 subunit-containing receptor, although its maximal effect was similar at the two receptor isoforms. 6. The GABA-mimetic action of etomidate was supported by β2- but not β1-subunit containing receptors, whereas that of pentobarbitone or propofol was evident with either β isoform. For β2-subunit containing receptors, both the agonist EC50 and the maximal current produced by etomidate were additionally influenced by the α isoform. 7. It is concluded that the subtype of β-subunit influences the potency with which etomidate potentiates GABA-evoked currents and that the β isoform is a crucial determinant of the GABA-mimetic activity of this compound. The nature of the α-subunit also impacts upon the maximal potentiation and activation that the compound may elicit. Such pronounced influences may aid the identification of the site that recognises etomidate. More generally, these results provide a clear example of structural specificity in anaesthetic action.

KW - 5α-pregnan-3α-ol-20-one

KW - Etomidate

KW - GABA(A) receptor

KW - GABA(A) receptor α, β and γ subunits

KW - Intravenous general anaesthetics

KW - Pentobarbitone

KW - Propofol

U2 - 10.1038/sj.bjp.0700927

DO - 10.1038/sj.bjp.0700927

M3 - Article

C2 - 9138677

AN - SCOPUS:0030895793

VL - 120

SP - 749

EP - 756

JO - British Journal of Pharmacology

JF - British Journal of Pharmacology

SN - 0007-1188

IS - 5

ER -