The δ subunit of γ-aminobutyric acid type A receptors does not confer sensitivity to low concentrations of ethanol

GABA(A) receptors (GABA(A)Rs) are usually formed by alpha, beta, and gamma or delta subunits. Recently, delta-containing GABA(A)Rs expressed in Xenopus oocytes were found to be sensitive to low concentrations of ethanol (1-3 mM). Our objective was to replicate and extend the study of the effect of ethanol on the function of alpha(4)beta(3)delta GABA(A)Rs. We independently conducted three studies in two systems: rat and human GABA(A)Rs expressed in Xenopus oocytes, studied through two-electrode voltage clamp; and human GABA(A)Rs stably expressed in the fibroblast L(tk(-)) cell line, studied through patch-clamp electrophysiology. In all cases, alpha(4)beta(3)delta GABA(A)Rs were only sensitive to high concentrations of ethanol (100 mM in oocytes, 300 mM in the cell line). Expression of the delta subunit in oocytes was assessed through the magnitude of the maximal GABA currents and sensitivity to zinc. Of the three rat combinations studied, alpha(4)beta(3) was the most sensitive to ethanol, isoflurane, and 5 alpha-pregnan-3 alpha, 21-diol-20-one (THDOC); alpha(4)beta(3)delta and alpha(4)beta(3)gamma(2S) were very similar in most aspects, but alpha(4)beta(3)delta was more sensitive to GABA, THDOC, and lanthanum than alpha(4)beta(3)gamma(2S) GABA(A)Rs. Ethanol at 30 mM did not affect tonic GABA-mediated currents in dentate gyrus reported to be mediated by GABA(A)Rs incorporating alpha(4) and delta subunits. We have not been able to replicate the sensitivity of alpha(4)beta(3)delta GABA(A)Rs to low concentrations of ethanol in four different laboratories in independent studies. This suggests that as yet unidentified factors may play a critical role in the ethanol effects on delta-containing GABA(A)Rs.