Pharmacological characterization of muscarinic receptor subtypes
| M1 | M2 | M3 | M4 | M5 | |
|---|---|---|---|---|---|
| Potency order | Acetylcholine and carbachol do not discriminate subtypes | ||||
| Selective agonists | |||||
| Antagonists4-a | |||||
| Atropine | 9.0–9.7 | 9.0–9.3 | 8.9–9.8 | 9.1–9.6 | 8.9–9.7 |
| Pirenzepine | 7.8–8.5 | 6.3–6.7 | 6.7–7.1 | 7.1–8.1 | 6.2–7.1 |
| 4-DAMP | 8.6–9.2 | 7.8–8.4 | 8.9–9.3 | 8.4–9.4 | 8.9–9.0 |
| Methoctramine | 7.1–7.8 | 7.8–8.3 | 6.3–6.9 | 7.4–8.1 | 6.9–7.2 |
| Himbacine | 6.9–7.4 | 8.0–8.3 | 6.9–7.4 | 8.0–8.8 | 6.1–6.3 |
| AF-DX 116 | 6.4–6.9 | 7.1–7.2 | 5.9–6.6 | 6.6–7.0 | 6.6 |
| AF-DX 384 | 7.3–7.5 | 8.2–9.0 | 7.2–7.8 | 8.0–8.7 | 6.3 |
| Tripitramine | 8.4–8.8 | 9.4–9.6 | 7.1–7.4 | 7.8–8.2 | 7.3–7.5 |
| pFHHSi D | 7.2–7.5 | 6.0–6.9 | 7.8–7.9 | 7.5 | 7.0 |
4-DAMP, 4-diphenylacetoxy-N-methyl piperidine methiodide. Antagonist affinities are expressed as −logK i or −log K B values. Adapted from Alexander and Peters (1999), Birdsall et al. (1998), Caulfield (1993), Caulfield et al. (1998), and Eglen and Watson (1996).
↵4-a No subtype-selective agonists of high intrinsic efficacy are available; thus, muscarinic receptor subtypes are pharmacologically defined by a combination of several antagonists.