This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autacoids, Subject name: Pharmacology
The following 5-HT receptor is not a G-protein coupled receptor 
Select and explain. 
A. 5-HT1, B. 5-HT2, C. 5-HT3, D. 5-HT4
C: 5-HT3
Answer: C: 5-HT3 
Explanation: Mech of action:- All 5-HT receptors (except 5-HT3) are G protein coupled receptors which function through decreasing (5-HT1) or increasing (5-HT4, 5-HT6, 5-HT7) cAMP production or by generating IP3/ DAG (5-HT2) as second messengers. The 5-HT3 is a ligand gated cation (Na+,K+) channel which on activation elicits fast depolarization. Ref:- kd tripathi; pg num:-171