Muscarinic acetylcholine receptors in the lung.

5 genetically distinct subtypes of muscarinic acetylcholine receptors have been cloned from human and rat tissues [l, 2 , 31 and these have been dubbed ml, m2, m3, m4 and m5. Each individual subtype has been expressed in animal cells and their pharmacology determined (4). It appears that the pharmacological subtypes Ml, M2 and M3 correspond to the cloned subtypes ml, m2 and m3. However, m4 and m5 do not appear to correspond to any of the pharmacological subtypes. The mRNA distribution of the cloned subtypes has been mapped in the brain and it has been found that all 5 subtypes are expressed