Table 2.

Main electrophysiological parameters of the different GABA_A receptor subtypes in standard ionic conditions (subunits expressed in Xenopus oocytes)

GABAA receptor subtype	Single-channel conductance (pS)	GABA EC50 (µM)	Hill coefficient	Characteristic time of desensitization td (s)	Characteristic time of deactivation (ms)	Activation time (ms)
α1β1γ1		1.2 [167]
α1β1γ2	30 [100]	4.5 [167] 6 [100]	1.2 [100]	0.492 [100] ([GABA] = 1 mM) 0.6 [103] ([GABA] = 100 µM)	20.5 [100] 17.4 [103]	1.1 [100] 1 [103] (γ2S splice variant)
α1β1γ3		0.6 [167]
α1β2γ1		0.67 [167] (human γ1, rat α1 and β2, expressed in 293 cells)
α1β2γ2	32 [152] 27.9 [56] (γ2S splice variant)	5 [172] 7 [110] (γ2S splice variant) 1.71 [177]	1.6 [110] (γ2S splice variant) 2.12 [152]	1.4 [110] (γ2S splice variant)	220 [110] (γ2S splice variant)
α1β2γ3	30.2 [178]	1.3 [167]
α1β2δ		6.71 [179]
α1β3γ1		2.1 [167]
α1β3γ2	28 [56] (γ2S splice variant) 27.5 [180]	1.7 [167] 2.9 [151] (γ2S splice variant) 7.6 [181] (γ2L splice variant) 14 [112] (γ2L splice variant) 36.2 [158] (γ2L splice variant) 14.1 [122] (γ2L splice variant)	1.7 [158] (γ2L splice variant)	0.424 [111] (average of 1 and 3 mM of GABA, γ2L splice variant) 0.95 [112] (γ2L splice variant, 1 mM of GABA)	68.6 [111] (γ2L splice variant) 143 [112] (γ2L splice variant) 82.5 [122] (γ2L splice variant)	0.55 [101] (γ2L splice variant) 0.603 [111] (γ2L splice variant)
α1β3δ	27.5 [180]	7.4 [181]			63.4 [181] 86.8 [123]
α2β1γ2	30 [100]	17 [184] 37 [100]	1.8 [100]	0.449 [100] ([GABA] = 1 mM)	198.7 [100] 82 (type 1) or 51 (type 2) [103]	0.5 [100] 0.5 [103] (γ2S splice variant)
α2β1ε		11.2 [185]
α2β2γ2		1.47 [177]
α2β3γ2		5.2 [151] (γ2S splice variant)		0.391 [111] (average of 1 and 3 mM of GABA, γ2L splice variant)	110.6 [111] (γ2L splice variant)	0.735 [111] (γ2L splice variant)
α3β1γ2		15.1 [167] (human α3, rat γ2 and β1, expressed in 293 cells)
α3β2γ2		130 [187] 15.1 [167] (human α3, rat γ2 and β2, expressed in 293 cells) 75 [110] (γ2S splice variant) 2.21 [177]	1.5 [110] (γ2S splice variant) 1.1 [187]	3.2 [110] (γ2S splice variant)	680 [110] (γ2S splice variant)
α3β3γ2		48 [151] (γ2S splice variant)		0.701 [111] (average of 1 and 3 mM of GABA, γ2S splice variant)	188.8 [111] (γ2L splice variant)	1.788 [111] (γ2L splice variant)
α4β1γ2		1.40 [177]
α4β1δ		0.30 [188] 0.17 [177]	1.57 [188]			174 [177]
α4β2γ2		3.9 [189] 1.4 [167]
α4β2δ		0.25 [179]
α4β3γ2		7.6 [151] (γ2S splice variant) 15 [112] (γ2L splice variant)		0.408 [111] (average of 1 and 3 mM of GABA, γ2L splice variant) 0.711 [112] (γ2L splice variant, 1 mM of GABA)	24.8 [111] (γ2L splice variant) 109 [112] (γ2L splice variant)	0.951 [111] (γ2L splice variant)
α4β3δ		0.35 [188]	1.8 [188]
α5β1γ2		5.6 [167]
α5β2γ2		5.8 [187] 4.2 [167] 0.47 [177]	1.5 [187]
α5β2γ3		4.9 [190]	1.9 [190]
α5β3γ2	24.9 [180]	11.6 [151] (γ2S splice variant)		1.315 [111] (average of 1 and 3 mM of GABA, γ2L splice variant)	41.5 [111] (γ2L splice variant)	1.247 [111] (γ2L splice variant)
α6β1γ2		0.5 [167]
α6β2γ1		0.4 [167]
α6β2γ2		5.2 [156] (γ2S splice variant) 1.4 [189] 0.34 [172] 0.50 [179] (γ2S splice variant)
α6β2δ		0.52 [156] (γ2S splice variant) 1.2 [167] 0.21 [179]
α6β3γ2		1 [151] (γ2S splice variant)		0.596 [111] (average of 1 and 3 mM of GABA, γ2L splice variant)	163.8 [111] (γ2L splice variant)	1.052 [111] (γ2L splice variant)
α6β3δ					340.4 [123]
ρ1		1.7 [116]	3.5 [116]	14.5 [116] (30 µM of GABA)		154 [116]
ρ2		2.6 [116]	3.3 [116]	8.2 [116] (30 µM of GABA)		180 [116]

Roman: rat subunits; bold: human subunits; bold italics: mouse subunits. The Hill coefficient, GABA EC50, main conductance state and characteristic times of activation, deactivation and desensitization of the most abundant subtypes in vivo, i.e. ternary subtypes and ρ homopentamers, are presented. Information on other subtypes can be found in [13, 103, 112, 114, 116, 123, 125, 130, 146, 152–157, 176, 180, 182, 191, 192]