Parameters determined from fitting Hill equation to pentobarbital concentration-response relationships. Numbers in parentheses indicate number of oocytes tested. For all pentobarbital-sensitive mutants, 2.5 mM pentobarbital was used (with exception of ρY198S/W328M and ρY198S/WVS328–330MGC receptor channels, where 1 mM pentobarbital was used) to obtain pentobarbital Imax (PbImax). Concentration of pentobarbital required for half-maximal activation (EC50), Hill coefficient and PbImax/GABA Imax are mean ± S.D.
| Subunit | EC50μM | Hill Coefficient | Pb Imax/GABA Imax |
|---|---|---|---|
| ρ1 (7) | No response up to 2.5 mM | ||
| α1β2γ2(4) | 659.3 ± 53.7 | 3.44 ± 0.66 | 0.16 ± 0.03 (3) |
| β2(3) | 49.7 ± 5.82-a | 0.96 ± 0.06 | |
| Chimeras | |||
| ρ324/β283(6) | pentobarbital activated2-b | ||
| ρ346/β305(3) | No response up to 2.5 mM | ||
| ρ405/β399(4) | No response up to 2.5 mM | ||
| ρ268/227–242/ρ285(4) | No response up to 2.5 mM2-a | ||
| ρ324/β283–304/ρ347(2) | 77.2 ± 0.5 | 1.74 ± 0.06 | |
| Point mutations | |||
| ρWV328,329MG (5) | 819.1 ± 156.1 | 1.42 ± 0.19 | Not determined |
| ρWVS328–330MGC (6) | 956.6 ± 140.3 | 2.19 ± 0.48 | Not determined |
| ρW328M (4) | 801.9 ± 144.7 | 1.32 ± 0.05 | 0.21 ± 0.12 (2) |
| ρV329G(4) | No response up to 2.5 mM | ||
| ρS330C (4) | No response up to 2.5 mM | ||
| ρVS329,330GC (3) | No response up to 2.5 mM | ||
| ρW328L (3) | 862.63 ± 139.9 | 1.45 ± 0.08 | 0.15 ± 0.06 (4) |
| ρW328I (2) | 2449.78 ± 163.38 | 1.06 ± 0.02 | 0.11 ± 0.05 (4) |
| ρW328V(3) | 1627.72 ± 224.54 | 1.81 ± 0.07 | 0.1 ± 0.05 (2) |
| ρW328A (3) | 1563.53 ± 181.75 | 1.78 ± 0.053 | 0.31 ± 0.06 (10) |
| ρW328F(7) | No response up to 2.5 mM | ||
| ρW328Y (7) | No response up to 2.5 mM | ||
| ρW328E (12) | No response up to 2.5 mM | ||
| ρW328P(8) | No response up to 2.5 mM | ||
| ρY198S/W328M (3) | 202.7 ± 23.5 | 1.14 ± 0.09 | 0.23 ± 0.01 (2) |
| ρY198S/WVS328–330MGC (3) | 176.5 ± 29.8 | 1.90 ± 0.21 | 0.35 ± 0.02 (2) |
| ρW328S (9) | No response up to 2.5 mM | ||
| ρWVS328–330GTC(5) | Depression in the maximum2-b | ||
| βM286W (5) | No response up to 2.5 mM | ||
| βMGC286–288WVS(5) | No response up to 2.5 mM | ||
| ρF333M (6) | No response up to 2.5 mM |