The GABA_A Receptor Gamma Subunit and Volatile Anesthetics

(supported by NIH grant R01GM866724)

Volatile anesthetics, like etomidate, positively modulate GABA_A receptors as well as glycine receptors. Sites for volatiles and alcohols on GABA_A and glycine receptors were identified by John Mihic, Neil Harrison, Adron Harris, and colleagues using a chimera strategy based on anesthetic insensitive homomeric GABA_C receptors (ρ subunits) and anesthetic-sensitive homomeric glycine receptors (α subunits). Subsequently, studies showed that mutations at homologous sites on GABA_A receptor α and β subunits could eliminate anesthetic modulation. These experiments were done in expressed GABA_A receptors that contained only α and β subunits, which probably do not exist in the nervous system.

We examined the impact of one of these mutations in GABA_A receptors containing a mutant α1 subunit combined with β2 and γ2L subunits. Using left-shift analysis, we found unexpectedly that the mutation did not alter volatile anesthetic modulation. However, when the γ2 subunit was removed, we found that anesthetic modulation of wild-type α1β2 receptors was larger than α1β2γ2L and that the α1 mutation completely eliminated anesthetic sensitivity ().

We are using chimeric subunits consisting of different regions of α1 and γ2L subunits co-expressed with β2 and α1, to identify those regions of γ2L that determine anesthetic sensitivity and that alter the impact of α1 mutants. Once these regions are identified, we will use single amino acid mutations to try and identify specific structures that are critical for the γ2 subunit effects. In addition, we are utilizing rapid kinetic studies to gain more insight into how the gamma subunit affects the basal and anesthetic-altered behavior of GABA_A receptors.

Related Links

Scheller & Forman, 2001

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