Binding protocols and drug affinities (Ki) at multiple histaminergic (H), muscarinic (M) and other binding sites as compared to dopamine D2 receptors
| Receptor | Tissue | Radioligand (nM) | Non-specific (μM) | Reference Ligand (Ki, nM) | S 16924 (Ki, nM) | Clozapine (Ki, nM) | Haloperidol (Ki, nM) |
|---|---|---|---|---|---|---|---|
| H1 | Cerebellum | [3H]Pyrilamine (1.0) | Promethazine (10) | Promethazine (0.4) | 158 ± 6 | 5.3 ± 0.4 | 453 ± 56 |
| (Guinea pig) | |||||||
| H2 | Cortex | [3H]Tiotidine (3.0) | Histamine (5000) | Cimetidine (833) | >1000 | 892 ± 19 | 573 ± 114 |
| M1 | Rat brain | [3H]QNB | >1000 | n.d. | n.d. | ||
| Human M1 | CHO cells | [3H]N-methyl-scopolamine (0.15) | Atropine (1.0) | Pirenzepine (8.5) | >1000 | 4.58 ± 0.96 | >1000 |
| Human M2 | CHO cells | [3H]N-methyl-scopolamine (0.5) | Atropine (1.0) | Methoctramine (14.9) | >1000 | 71.9 ± 19 | >1000 |
| Human M3 | CHO cells | [3H]N-methyl-scopolamine (0.5) | Atropine (1.0) | 4-DAMP (1.1) | >1000 | 39.1 ± 6.1 | >1000 |
| Human M4 | CHO cells | [3H]N-methyl-scopolamine (0.25) | Atropine (1.0) | 4-DAMP (1.9) | >1000 | 35.5 ± 5.5 | >1000 |
| NMDA | Rat cortex | [3H]CGP 39653 (2.0) | L-glutamate (100) | CGS 19755 (600) | >1000 | n.d. | n.d. |
| AMPA | Rat cortex | [3H]AMPA (5.0) | L-glutamate (1.0) | L-glutamate (890) | >1000 | n.d. | n.d. |
| GABAA | Rat cortex | [3H]Muscimol (2.5) | Muscimol (10.0) | Muscimol (10) | >1000 | n.d. | n.d. |
| GABAB | Rat cortex | [3H]GABA (10) | Baclofen (100) | Baclofen (150) | >1000 | n.d. | n.d. |
| BZC | Rat brain | [3H]Flunitrazepam (0.4) | Diazepam (3.0) | Diazepam (13) | >1000 | n.d. | n.d. |
Mean ± S.E.M. for n ≥ 3 determinations; n.d., not determined. NMDA, N-Methyl-d-Aspartate; AMPA, (dl-α-NH2-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid); GABA, gamma-amino butyric acid; BZC, benzodiazepine.