Stoichiometry of a recombinant GABAA receptor deduced from mutation-induced rectification.

Ligand-gated ion channels generally display a heterooligomeric subunit structure. The present report describes an electrophysiological method that provides criteria indicating the subunit stoichiometry of a recombinant GABAA receptor composed of alpha 3, beta 2 and gamma 2 subunits. Our results exclude the stoichiometries 3 alpha 1 beta 1 gamma, 1 alpha 3 beta 1 gamma, 1 alpha 1 beta 3 gamma and suggest that the possible subunit stoichiometries for this receptor are 2 alpha 1 beta 2 gamma, 2 alpha 2 beta 1 gamma or 1 alpha 2 beta 2 gamma, of which the alpha subunit composition 2 alpha 1 beta 2 gamma may be favoured. The method is based on the quantification of the outward rectification of the GABA-evoked current induced by point mutation of charged amino acids located near the ion channel pore.