D2O discriminates gamma aminobutyric acid A receptors with different lifetimes

Progress of gamma aminobutyric acidA receptor channel (GABAAR) mediated 36Cl-ion uptake by native membrane vesicles from the rat cerebral cortex has been examined using rapid kinetic techniques. Data on GABA responsive 36Cl-ion flux, measured in a series of buffered salt solutions made up of different H2O-D2O mixtures, were evaluated by fitting a model with the mechanisms of channel opening and desensitization of GABAAR. The overall isotope effect could be isolated into its component contributions from the GABAARs by their different active lifetimes. Ion flux mediated by the slower desensitizing GABAAR was completely inhibited by 20% D2O. Large and selective D2O effects on ion fluxes mediated by the kinetically distinguishable native GABAARs suggest distinct types of subunit combinations for these receptors.