<prompt> Methacholine is a:AIIMS May 2015, May 2014M1 receptor agonistM2 receptor agonistM3 receptor agonistM4 receptor agonist  <response>: Ans. b. M2 receptor agonist Ref: KDT 7e p101; Katzung p100Methacholine is a M2 receptor agonist. M1M2M3Location and functionAutonomic ganglia:Depolarization late EPSPGastric glands: Histamine release and acid secretionQCNS: Learning, memory and motor functionsQSA node: Hyperpolarization, rate of impulse generationQAV node: velocity of conductionAtrium: Shortening of APD, contractilityQVentricle: contractility slight as receptors are sparseCholinergic nerve endings: ACh releaseQCNS: Tremors, analgesiaVisceral smooth muscles: ContractionQVisceral smooth muscles: ContractionQIris: Constriction of pupilQ Ciliary muscles: ContractionQExocrine glands:SecretionQVascular endothelium:Release of NO - VasodilationQNatureGq-protein coupledGiGo protein coupledGq-protein coupledTransducer mechanismIP3DAG - cytosolic calcium; PLA2 - PG synthesisK channel opening, cAMPIP3DAG - cytosolic calcium;PLA2 - PG synthesisAgonistsRelatively selectiveOxotremorine, MCN- 343AMethacholineQBethanecholAntagonistsRelatively selectivePirenzepine,TelenzepineMethoctramine, TripitramineDarifenacin, Solefenacin 