The interaction of the general anesthetic etomidate with the γ-aminobutyric acid type A receptor is influenced by a single amino acid

D Belelli, JJ Lambert, JA Peters… - Proceedings of the …, 1997 - National Acad Sciences
D Belelli, JJ Lambert, JA Peters, K Wafford, PJ Whiting
Proceedings of the National Academy of Sciences, 1997National Acad Sciences
The γ-aminobutyric acid type A (GABAA) receptor is a transmitter-gated ion channel
mediating the majority of fast inhibitory synaptic transmission within the brain. The receptor
is a pentameric assembly of subunits drawn from multiple classes (α1–6, β1–3, γ1–3, δ1,
and ɛ1). Positive allosteric modulation of GABAA receptor activity by general anesthetics
represents one logical mechanism for central nervous system depression. The ability of the
intravenous general anesthetic etomidate to modulate and activate GABAA receptors is …
The γ-aminobutyric acid type A (GABAA) receptor is a transmitter-gated ion channel mediating the majority of fast inhibitory synaptic transmission within the brain. The receptor is a pentameric assembly of subunits drawn from multiple classes (α1–6, β1–3, γ1–3, δ1, and ɛ1). Positive allosteric modulation of GABAA receptor activity by general anesthetics represents one logical mechanism for central nervous system depression. The ability of the intravenous general anesthetic etomidate to modulate and activate GABAA receptors is uniquely dependent upon the β subunit subtype present within the receptor. Receptors containing β2- or β3-, but not β1 subunits, are highly sensitive to the agent. Here, chimeric β12 subunits coexpressed in Xenopus laevis oocytes with human α6 and γ2 subunits identified a region distal to the extracellular N-terminal domain as a determinant of the selectivity of etomidate. The mutation of an amino acid (Asn-289) present within the channel domain of the β3 subunit to Ser (the homologous residue in β1), strongly suppressed the GABA-modulatory and GABA-mimetic effects of etomidate. The replacement of the β1 subunit Ser-290 by Asn produced the converse effect. When applied intracellularly to mouse L(tk−) cells stably expressing the α6β3γ2 subunit combination, etomidate was inert. Hence, the effects of a clinically utilized general anesthetic upon a physiologically relevant target protein are dramatically influenced by a single amino acid. Together with the lack of effect of intracellular etomidate, the data argue against a unitary, lipid-based theory of anesthesia.
National Acad Sciences