TABLE 1

Properties of GABAergic agonists

A summary of the activation properties of the GABAergic agonists employed in the study. Wild type is the ternary GABA_A receptor consisting of βαγ + βα concatemeric constructs and α1(L263S) is the receptor consisting of βα(L263S)γ and βα(L263S) concatemeric constructs. The parameter K_X is the equilibrium dissociation constant of the closed receptor for a given agonist. The parameter c_X gives the ratio of the dissociation constants of the open receptor to that of the closed receptor. The parameter N_X is the number of binding sites for the agonist. Gating energy was calculated as N_XRT × ln(c_X). The maximal predicted open probability (P_open,max) was calculated as 1/(1 + Lc_X^N) with L held at 8000 for the wild-type receptor (Akk et al., 2018) and 8.1 for the mutant receptor (Shin et al., 2018).

Receptor	Agonist	K_X	c_X	N_X	Gating Energy	P_open,max
		μM			kcal/mol
Wild type	GABA^{^a}	72 ± 15	0.003 ± 0.000	2	−6.74	0.92
Wild type	P4S	38 ± 4	0.027 ± 0.000	2	−4.26	0.15
Wild type	β-Alanine	6664 ± 2947	0.002 ± 0.001	2	−7.17	0.96
Wild type	Propofol^{^a}	21 ± 3	0.222 ± 0.003	6	−5.33	0.51
Wild type	Pentobarbital	1912 ± 1690	0.004 ± 0.002	2	−6.52	0.89
Wild type	Alfaxalone^{^b}	2.3 ± 0.3	0.159 ± 0.009	2	−2.17	0.005
Wild type	3α5αP^{^b}	0.27 ± 0.07	0.233 ± 0.018	2	−1.72	0.002
Wild type	3α5βP^{^b}	0.45 ± 0.06	0.265 ± 0.010	2	−1.57	0.002
Wild type	ent-3α5βP^{^b}	2.4 ± 0.4	0.166 ± 0.012	2	−2.12	0.005
α1(L263S)	Alfaxalone	3.0 ± 0.3	0.130 ± 0.006	2	−2.41	0.88
α1(L263S)	Etiocholanolone	11.1 ± 1.5	0.685 ± 0.009	2	−0.45	0.21

↵^a The data for GABA and propofol are from prior reports (Akk et al., 2018; Shin et al., 2018).
↵^b The wild-type concatemeric receptor is only weakly activated by neuroactive steroids. Accordingly, the properties of the steroids alfaxalone, 3α5αP, 3α5βP, and ent-3α5βP were determined in the presence of a low concentration (∼EC₁₀) of GABA.