Binding properties of M2 and M3 receptors
The hM2′ construct is the hM2 receptor with 1× HA tagging after the initiating Met residue and deletion of potential N-glycosylation sites (see Materials and Methods). The rM3′ construct is the rM3 receptor with 1× HA tagging after the initiating Met residue, deletion of potential N-glycosylation sites, and a large deletion from Ala274 to Lys469 in the center portion of the third intracellular loop (Zeng et al., 1999). The t1/2 values represent the mean ± S.E.M. from three or more assays and are the standard half times of [3H]NMS dissociation in the presence of atropine. Bmax and pKd values are the mean ± S.E.M. from two or more assays.
Receptor | t1/2 | pKd | Bmax |
|---|---|---|---|
| min | pmol / mg protein | ||
| hM2 | 4.0 ± 0.2 | 10.30 ± 0.07 | 4.81 ± 0.69 |
| hM2′ | 3.5 ± 0.2 | 9.99 ± 0.13 | 1.95 ± 0.39 |
| hM2′, 6.5% labeling | 3.1 ± 0.2 | ||
| hM2′ C96A, C176A | 1.7 ± 0.2 | 9.43 ± 0.15 | 0.03 ± 0.01 |
| hM2 C413A, C416A | 2.7 ± 0.1 | 9.82 ± 0.20 | 4.51 ± 1.16 |
| hM3 | 22.0 ± 1.4 | 10.35 ± 0.12 | 6.78 ± 2.79 |
| hM3 C141A, C221A | 3.9 ± 0.2 | 9.16 ± 0.06 | 0.12 ± 0.02 |
| hM3 C517A, C520A | 19.4 ± 1.1 | 9.97 ± 0.07 | 4.47 ± 1.33 |
| rM3′ | 56.5 ± 2.5 | 10.52 ± 0.11 | 4.30 ± 0.80 |
| rM3′, 8.2% labeling | 42.0 ± 6.4 | ||
| rM3′ C141A, C220A | 4.2 ± 0.2 | 8.99 ± 0.08 | 0.27 ± 0.10 |