Fitted propofol and pentobarbital binding and gating parameters for allosteric activation model
Pooled Po data from at least four cells were fitted with eq. 2 (Materials and Methods). Lo was calculated as (1 − Po,spont)/Po,spont, equaling 6.7 (for wild type), 13.3 (H267W), 99 (L268W), 0.7 (F221W), 3.8 (Y143W), or 1.9 (T266W). For Q224W, which showed no spontaneous activity, we used an arbitrary Lo value of 1000. KC is the equilibrium dissociation constant for closed receptors. Parameter d equals the ratio of open receptor and closed receptor dissociation constants (KO/KC), and is a measure of gating efficacy (large values denote poor efficacy). The goodness of the fit showed minimal changes when the number of propofol or pentobarbital binding sites varied between three and five. The parameters in the table are from fits with five propofol and four pentobarbital binding sites.
| Receptor | KC, propofol | d, propofol | KC, pentobarbital | d, pentobarbital |
|---|---|---|---|---|
| µM | µM | |||
| β3 wild type | 8.8 | 0.64 | 1022 | 0.07 |
| β3(H267W) | 7.1 | 0.67 | 3482 | 0.02 |
| β3(L268W) | 6.5 | 0.55 | 359 | 0.16 |
| β3(Q224W) | NA | NA | 2401 | 0.05 |
| β3(F221W) | NA | NA | >40 mM | 0.06 |
| β3(Y143W) | 14.4 | 0.91 | 118 | 0.34 |
| β3(T266W) | NA | NA | 1503 | 0.34 |
NA, not available (responses were too small for analysis).