M₁, M₃ and M₅ muscarinic receptors stimulate mitogen-activated protein kinase

We report here that the M₁, M₃ and M₅ muscarinic acetylcholine receptor subtypes that have been shown to couple to phosphoinositide hydrolysis also activate the mitogen-activated protein kinase (MAPK). Pharmacological characterization as well as mechanistic details of the activation pathway are presented. Carbachol-induced MAPK activation was time- and concentration-dependent at all subtypes. Pharmacological characterization of the MAPK response revealed that McN-A-343 was a partial agonist at the M₁ and M₃ subtypes, and that pilocarpine was a partial agonist at the M₃ and M₅ receptors. Carbachol-mediated MAPK activation at these receptor subtypes was pertussis toxin and wortmannin insensitive. By contrast, both agents significantly inhibited carbachol-induced MAPK activation by the M₂ muscarinic receptor subtype. Furthermore, two independent single point mutations in the M₁ receptor attenuated carbachol-induced activation of MAPK. Activation of MAPK at the M₁, M₃ and M₅ muscarinic receptor subtypes was not dependent on intracellular or extracellular Ca²⁺, but was partially dependent upon protein kinase C. These data suggest that activation of MAPK by M₁, M₃ and M₅ muscarinic receptors involves protein kinase C-dependent and independent pathways.