title: Functional activity of the M2 and M4 receptor subtypes in the spinal cord studied with muscarinic acetylcholine receptor knockout mice.
abstract: Stimulation of spinal muscarinic acetylcholine receptors (mAChRs) produces potent analgesia. Both M(2) and M(4) mAChRs are coupled to similar G proteins (G(i/o) family) and play a critical role in the analgesic action of mAChR agonists. To determine the relative contribution of M(2) and M(4) subtypes to activation of G(i/o) proteins in the spinal cord, we examined the receptor-mediated guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding in M(2) and M(4) subtype knockout (KO) mice. Basal [(35)S]GTPgammaS binding in the spinal cord was similar in the wild-type controls, M(2) and M(4) single-KO, and M(2)/M(4) double-KO mice. The spinal [(35)S]GTPgammaS binding stimulated by either muscarine or oxotremorine-M was not significantly different among three groups of wild-type mouse strains. In M(2) single-KO and M(2)/M(4) double-KO mice, the agonist-stimulated [(35)S]GTPgammaS binding was completely abolished in the spinal cord. Furthermore, the agonist-stimulated [(35)S]GTPgammaS binding in the spinal cord of M(4) single-KO mice was significantly reduced ( approximately 15%), compared with that in wild-type controls. On the other hand, the spinal [(35)S]GTPgammaS binding stimulated by a mu-opioid agonist was not significantly different between wild-type and M(2) and M(4) KO mice. This study provides complementary new evidence that M(2) is the most predominant mAChR subtype coupled to the G(i/o) proteins in the spinal cord. Furthermore, these data suggest that a small but functionally significant population of M(4) receptors exists in the mouse spinal cord. The functional activity of these M(4) receptors seems to require the presence of M(2) receptors.
authors.affiliation: Department of Anesthesiology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
authors.forename: Shao-Rui
authors.initials: SR
authors.lastname: Chen
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wess
authors.forename: Hui-Lin
authors.initials: HL
authors.lastname: Pan
mesh_terms: D000818:Animals; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010095:Oxotremorine / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000172:deficiency* / Q000235:genetics*; D043588:Receptor, Muscarinic M4 / Q000819:agonists / Q000172:deficiency* / Q000235:genetics*; D011976:Receptors, Muscarinic / Q000172:deficiency / Q000235:genetics; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*
chemical_list: D043585:Receptor, Muscarinic M2; D043588:Receptor, Muscarinic M4; D011976:Receptors, Muscarinic; D010095:Oxotremorine