You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Methacholine is a:(AIIMS May 2015, May 2014) and explain in detail?
Ans. b. M2 receptor agonist (Ref: KDT 7/e p101; Katzung p100)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 coupledTransducer mechanismIP3/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