Butanol effects on gamma-amino butyric acid concentration-responses in human alpha1beta2gamma2L gamma-amino butyric acid type A receptors with a mutation at alpha1S270.

摘要

Alcohol enhancement of gamma-amino butyric acid type A receptor (GABA(A)R) gating at low GABA is reduced by a serine-to-isoleucine mutation at residue alphaS270, suggesting that alphaS270 forms an enhancement site. However, whether the alphaS270I mutation strengthens alcohol inhibition of GABA(A)Rs remains unexplored. Furthermore, alphaS270 mutations have not been studied in the most prevalent form of mammalian GABA(A)Rs consisting of alpha1, beta2, and gamma2 subunits. In voltage-clamped Xenopus oocytes expressing recombinant alpha1beta2gamma2L GABA(A)Rs, electrophysiological analysis of GABA concentration-responses demonstrates that the alpha1(S270I) mutation increases apparent GABA affinity and significantly reduces the Hill coefficient of GABA(A)R activation. Butanol-induced leftward-shifts in GABA concentration-responses for both wild-type alpha1beta2gamma2L and alpha1(S270I)beta2gamma2L GABA(A)Rs are equal. At high GABA, butanol neither enhances nor inhibits alpha1(S270I)beta2gamma2L responses. Thus, in the dominant mammalian GABA(A)R isoform, the alphaS270I 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.