PT - JOURNAL ARTICLE AU - Shao-Rui Chen AU - Jürgen Wess AU - Hui-Lin Pan TI - Functional Activity of the M<sub>2</sub> and M<sub>4</sub> Receptor Subtypes in the Spinal Cord Studied with Muscarinic Acetylcholine Receptor Knockout Mice AID - 10.1124/jpet.104.082537 DP - 2005 May 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 765--770 VI - 313 IP - 2 4099 - http://jpet.aspetjournals.org/content/313/2/765.short 4100 - http://jpet.aspetjournals.org/content/313/2/765.full SO - J Pharmacol Exp Ther2005 May 01; 313 AB - Stimulation of spinal muscarinic acetylcholine receptors (mAChRs) produces potent analgesia. Both M2 and M4 mAChRs are coupled to similar G proteins (Gi/o family) and play a critical role in the analgesic action of mAChR agonists. To determine the relative contribution of M2 and M4 subtypes to activation of Gi/o proteins in the spinal cord, we examined the receptor-mediated guanosine 5′-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding in M2 and M4 subtype knockout (KO) mice. Basal [35S]GTPγS binding in the spinal cord was similar in the wild-type controls, M2 and M4 single-KO, and M2/M4 double-KO mice. The spinal [35S]GTPγS binding stimulated by either muscarine or oxotremorine-M was not significantly different among three groups of wild-type mouse strains. In M2 single-KO and M2/M4 double-KO mice, the agonist-stimulated [35S]GTPγS binding was completely abolished in the spinal cord. Furthermore, the agonist-stimulated [35S]GTPγS binding in the spinal cord of M4 single-KO mice was significantly reduced (∼15%), compared with that in wild-type controls. On the other hand, the spinal [35S]GTPγS binding stimulated by a μ-opioid agonist was not significantly different between wild-type and M2 and M4 KO mice. This study provides complementary new evidence that M2 is the most predominant mAChR subtype coupled to the Gi/o proteins in the spinal cord. Furthermore, these data suggest that a small but functionally significant population of M4 receptors exists in the mouse spinal cord. The functional activity of these M4 receptors seems to require the presence of M2 receptors. The American Society for Pharmacology and Experimental Therapeutics