New subtypes of muscarinic acetylcholine receptors.

Human and rat genes and/or cDNAs for five different mAChRs have been cloned. The m1, m2 and m3 receptors correspond most closely to the pharmacologically defined M1, M2 and M3 receptors and are expressed in both brain and peripheral tissues. The m4 and m5 receptors are previously unrecognized pharmacological subtypes whose mRNAs are found predominantly in brain. Other less related but uncharacterized genes could represent additional subtypes. The properties of the five receptors and their genes are reviewed and their implications for future research are discussed.