TABLE 1

GABA concentration-response properties of the concatameric receptors

The table shows the results from fitting the GABA concentration-response data to the Hill equation. The data were normalized to the response obtained at 1 mM GABA. The first row (αβγ) gives the results obtained from receptors containing free α1, β2. and γ2L subunits (from Akk et al., 2011). The lower range of peak responses is due to a type of chamber used in which only a portion of the cell membrane is exposed to drugs. Receptors containing two mutated β subunits showed negligible currents in the presence of 1 mM GABA (less than 10 nA).

ReceptorConfigurationMaximal ResponseEC50nHNo. of CellsRange of Currents at Maximal GABA
μMnA
αβγGS/GS1.0 ± 0.034.6 ± 0.41.4 ± 0.17675–1780
βαγ-βαGS/GS1.0 ± 0.0333 ± 22.0 ± 0.354364–6075
βαγ-β*αGS/–S1.0 ± 0.0295 ± 61.4 ± 0.16827–2443
βαγ-βα*GS/G–1.0 ± 0.0176 ± 31.9 ± 0.151831–5133
βαγ-β*α*GS/– –1.0 ± 0.0279 ± 41.6 ± 0.151171–4403
βα*γ-βαG–/GS1.0 ± 0.0253 ± 41.3 ± 0.153370–4592
βα*γ-β*αG–/–S1.1 ± 0.194 ± 231.0 ± 0.24129–211
βα*γ-βα*G–/G–1.1 ± 0.03156 ± 121.4 ± 0.15487–1212
βα*γ-β*α*G–/– –1.1 ± 0.01126 ± 51.2 ± 0.05692–263
β*αγ-βα–S/GS1.0 ± 0.0232 ± 21.1 ± 0.14277–2823
β*αγ-β*α–S/–SN.D.N.D.N.D.5<5
β*αγ-βα*–S/G–1.1 ± 0.02140 ± 111.2 ± 0.1735–142
β*αγ-β*α*–S/– –N.D.N.D.N.D.5<5
β*α*γ-βα– –/GS1.1 ± 0.124 ± 61.0 ± 0.25460–3851
β*α*γ-β*α– –/–SN.D.N.D.N.D.6<10
β*α*γ-βα*– –/G–1.2 ± 0.02187 ± 131.1 ± 0.1550–148
β*α*γ-β*α*– –/– –N.D.N.D.N.D.4<10
  • β*, β(Y205S); α*, α(Q241L); G, intact GABA site; S, intact steroid site; N.D., not determined.