TABLE 1

Functional properties of GABA and methaqualone determined by two-electrode voltage-clamp electrophysiology at human GABA_ARs expressed in Xenopus oocytes

Unless otherwise indicated in the footnotes to this table, data given for methaqualone represents its properties as a positive allosteric modulator determined at the receptors in the presence of GABA EC₁₀. EC₅₀ values are given in μM with pEC₅₀ ± S.E.M. values in brackets, and R_max values are given in percentage of the R_max value of GABA at the receptor (n indicates number of experiments performed).

	GABA		Methaqualone
	EC₅₀ (pEC₅₀ ± S.E.M.)	n	EC₅₀ (pEC₅₀ ± S.E.M.)	R_max ± S.E.M.	n
α₁β₂	7.8 (5.11 ± 0.05)	6	49 (4.31 ± 0.03)	79 ± 3.7	6
α₁β₂γ_2S	57 (4.25 ± 0.10)	6	38 (4.41 ± 0.03)	84 ± 2.1	7
α₁β₃γ_2S	34 (4.46 ± 0.18)	5	30 (4.52 ± 0.03)	77 ± 2.2	6
α₂β₂γ_2S	40 (4.40 ± 0.07)	4	24 (4.61 ± 0.03)	75 ± 2.1	9
α₃β₂γ_2S	120 (3.94 ± 0.03)	7	49 (4.31 ± 0.12)	66 ± 2.4	4
α₄β₁δ^a monophasic	0.46 (6.33 ± 0.44)	3	n.d.	n.d.
α₄β₁δ^a biphasic	0.034 (7.47 ± 0.54)
	1.2 (5.91 ± 0.51)	4	n.d.	n.d.	12^{^a}
α₄β₂δ	2.2 (5.65 ± 0.10)	7	68 (4.17 ± 0.06)	240 ± 27	5
α₄β₃δ	0.012 (7.94 ± 0.16)
	3.1 (5.51 ± 0.14)	5	120 (3.91 ± 0.14)^{^b}	230 ± 12^{^b}	6^{^b}^,^{^c}
α₅β₂γ_2S	31 (4.50 ± 0.06)	6	28 (4.56 ± 0.04)	73 ± 1.6	6
α₆β₁δ	1.4 (5.85 ± 0.08)	6	∼100 (∼4.0)^{^d}		5^{^d}
α₆β₂	0.28 (6.54 ± 0.07)	7	74 (4.13 ± 0.02)	220 ± 25	4
α₆β₂δ	0.30 (6.52 ± 0.04]	6	36 (4.44 ± 0.04)	280 ± 22	8
α₆β₃δ	0.60 (6.23 ± 0.03)	8	31 (4.50 ± 0.04)	110 ± 21	7
α₁^M236Wβ₂γ_2S	4.1 (5.39 ± 0.11)	6	88 (4.06 ± 0.03)^{^b}	60 ± 4.8^{^b}	4^{^b}^,^{^c}
α₁β₂^M286Wγ_2S	5.4 (5.26 ± 0.07)	6	25 (4.60 ± 0.22)	41 ± 2.6	5
α₆β₁^S265Nδ	0.90 (6.05 ± 0.02)	5	96 (4.02 ± 0.03)	230 ± 24	5^{^c}
α₆β₂^N265Sδ	0.30 (6.53 ± 0.02)	4	∼300 (∼3.5)^{^d}		7^{^d}

n.d., not determinable.
↵^a GABA displayed monophasic and biphasic concentration-response curves at three and four of seven α₄β₁δ-expressing oocytes, respectively. Methaqualone was tested as a positive and negative allosteric modulator at both oocyte populations.
↵^b Properties of methaqualone as an agonist at α₄β₃δ and α₁^M236Wβ₂γ_2S GABA_ARs. Agonist EC₅₀ values are given in μM with pEC₅₀ ± S.E.M. values in brackets, and R_max values are given in percentage of the R_max value of GABA at the receptor.
↵^c The concentration-response curve was not completely saturated at the highest methaqualone concentration tested. EC₅₀ (pEC₅₀) and R_max values have been extracted from the fitted curve.
↵^d Properties of methaqualone as a negative allosteric modulator at α₆β₁δ and α₆β₂^N265Sδ GABA_ARs determined in the presence of GABA EC_60–70. Estimated IC₅₀ values are given in μM with pIC₅₀ in brackets.