Parameter estimates of thiochrome binding from equilibrium assays with [3H]NMS and ACh Parameters (mean ± S.E.M.) were estimated from fitting assays such as those shown in (Figs. 2 and 3A to the allosteric model using nonlinear regression analysis. Thiochrome was inactive at M5 receptors at concentrations up to 0.3 mM, the highest concentration used in these assays (n = 2). The slope factor for thiochrome binding was fixed at 1. pK is log affinity (M—1) of thiochrome for the free receptor; Coop NMS is the estimate of the cooperativity of thiochrome with [3H]NMS, and Coop ACh is the estimate of the cooperativity of thiochrome with ACh. n indicates the number of assays.
| Subtype | pK | Coop NMS | Coop ACh | n |
|---|---|---|---|---|
| M1 | 4.07 ± 0.23 | 0.74 ± 0.16 | 1.07 ± 0.17 | 4 |
| M2 | 3.92 ± 0.23 | 0.94 ± 0.25 | 0.90 ± 0.28 | 5 |
| M3 | 4.44 ± 0.21 | 0.62 ± 0.13 | 0.82 ± 0.24 | 6 |
| M4 | 4.01 ± 0.12 | 0.72 ± 0.16 | 3.90 ± 0.59 | 7 |
| M5 | N.E. |
N.E., no effect.