Fig. 5.  Monod–Wyman–Changeux two-state equilibrium model for etomidate and GABA activation of GABA^Areceptors. The scheme depicts allosteric coagonism for GABA^Areceptors with two equivalent GABA (G ; orthosteric agonist) sites and two equivalent etomidate (E ; allosteric agonist) sites. The L⁰parameter describes the basal equilibrium between the two canonical states: inactive (R ) and active (O ). K^Gis the dissociation constant for GABA interactions with R -state receptors; and K^G* is the dissociation constant for GABA interactions with O -state receptors. The GABA efficacy factor, c , is defined as K^G*/K^G. K^Eis the dissociation constant for etomidate interactions with R -state receptors; and K  ^E* is the dissociation constant for etomidate interactions with O -state receptors. The etomidate efficacy factor, d , is defined as K^E*/K^E. The differently sized arrows  illustrate how equilibria shift as ligands bind and functional state changes.