PT  - JOURNAL ARTICLE
AU  - M Waelbroeck
AU  - M Tastenoy
AU  - J Camus
AU  - J Christophe
TI  - Binding of selective antagonists to four muscarinic receptors (M1 to M4) in rat forebrain.
DP  - 1990 Aug 01
TA  - Molecular Pharmacology
PG  - 267--273
VI  - 38
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/38/2/267.short
4100  - http://molpharm.aspetjournals.org/content/38/2/267.full
SO  - Mol Pharmacol1990 Aug 01; 38
AB  - To compare the proportions of four muscarinic receptors in different rat brain regions, we used competition curves with four selective antagonists, at 1-[N-methyl-3H]scopolamine methyl chloride [( 3H]NMS) binding equilibrium and after allowing [3H]NMS dissociation for 35 min. Himbacine and methoctramine were shown to discriminate two muscarinic receptor subtypes having a high affinity for 4-diphenylacetoxy-N-methylpiperidine methiodide and hexahydrosiladifenidol, intermediate affinity for pirenzepine, and low affinity for AF-DX 116. One M4 subtype had a high affinity for himbacine and methoctramine; it was found predominantly in homogenates from rat striatum (46% of total [3H]NMS receptors) and in lower proportion in cortex (33% of [3H]NMS receptors) and hippocampus (16% of [3H]NMS receptors). Its binding properties were identical to those of muscarinic receptors in the neuroblastoma x glioma NG 108-15 hybrid, suggesting that it was encoded by m4 mRNA. The M3 subtype (typically found in rat pancreas, a tissue expressing the m3 mRNA) had a low affinity for himbacine and methoctramine and represented about 10% of all [3H]NMS receptors in rat brain cortex, hippocampus, striatum, and cerebellum. M1 and M2 receptors were identified in rat brain by their high affinity for pirenzepine and AF-DX 116, respectively.