This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Pharmacology, Subject name: Pharmacology
Which of the following act through G protein coupled receptors? 
Select and explain. 
A. Ach Muscarinic receptors, B. Insulin receptors, C. Ach Nicotinic receptors, D. GABA-A receptors
A: Ach Muscarinic receptors
Answer: A: Ach Muscarinic receptors 
Explanation: (a) Ach Muscarinic receptors,Ref: Lippincott, 6th ed., pg. 27-28* M1,M2,M3,M4 and M5 are Ach Muscarinic receptors. They are G protein coupled receptors.* M1 and M3 acts trough Gq protein, activates IP3/DAG and increase cytosolic calcium while M2 receptors involve Gi protein, inhibits adenylyl cyclase and increases potassium conductance.* Insulin receptors are a member of the ligand-activated receptor and tyrosine kinase family of transmembrane signaling proteins* Ach Nicotinic receptors are Ionotropic receptors or ion-channel coupled receptors* GABA-A receptors are also Ionotropic receptors or ion-channel coupled receptors. Glutamate receptors, glycine receptors are other examples of Ionotropic receptors.