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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
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Methacholine acts at which receptor?(AIIMS May 2015. May 2014)
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The correct answer is  Ans. b. M2 (Ref: Goodman Gillman 12/e p; Katzung 12/e p100; KDT 7/e p101)Methacholine is a M2 receptor agonist. M1M2M3Location and functionAutonomic ganglia:Depolarization (late EPSP)Gastric 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 sparse)Cholinergic 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 coupledGi/Go protein coupledGq-protein coupledTransducermechanismIP3/DAG - | cytosolic calcium; | PLA2 - PG synthesisK+ channel opening, | cAMPIP3/DAG -| cytosolic calcium;|PLA2 - PG synthesisAgonists(Relatively selective)Oxotremorine, MCN- 343AMethacholineQBethanecholAntagonists(Relatively selective)Pirenzepine,TelenzepineMethoctramine, TripitramineDarifenacin, Solefenacin