Additional evidence from co-localization, co-immunprecipitation and neuronal electrophysiology studies also suggests that γ2 or δ subunits partner with more than one β subunit (one at a time). In addition, point mutations in the M2 domain (M2-15´) that can produce β subunit selectivity for loreclezole or etomidate (Cestari and Yang, 1996; Belelli et al., 1997; Rudolph and Antkowiak, 2004) provided evidence for the existence of receptor subtypes with specific β subunits. So far, these results did not provide evidence on whether the γ2 or δ subunit-containing receptors, or both mediate the etomidate effects identified, although the δ-containing receptors are more sensitive to modulation. In addition, the respective α subunits present in these receptor also could not be identified.
