Butanol effects on γ-amino butyric acid concentration-responses in human α 1β 2γ 2L γ-amino butyric acid type A receptors with a mutation at α 1S270

Abstract

Alcohol enhancement of γ-amino butyric acid type A receptor (GABA AR) gating at low GABA is reduced by a serine-to-isoleucine mutation at residue αS270, suggesting that αS270 forms an enhancement site. However, whether the αS270I mutation strengthens alcohol inhibition of GABA ARs remains unexplored. Furthermore, αS270 mutations have not been studied in the most prevalent form of mammalian GABA ARs consisting of α 1, β 2, and γ 2 subunits. In voltage-clamped Xenopus oocytes expressing recombinant α 1β 2γ 2L GABA ARs, electrophysiological analysis of GABA concentration-responses demonstrates that the α 1(S270I) mutation increases apparent GABA affinity and significantly reduces the Hill coefficient of GABA AR activation. Butanol-induced leftward-shifts in GABA concentration-responses for both wild-type α 1β 2γ 2L and α 1(S270I)β 2γ 2L GABA ARs are equal. At high GABA, butanol neither enhances nor inhibits α 1(S270I)β 2γ 2L responses. Thus, in the dominant mammalian GABA AR isoform, the αS270I mutation affects neither enhancement nor inhibition by butanol, but alters the gating mechanism by reducing cooperativity, producing an apparent reduction in alcohol enhancement at low GABA.