This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of the following receptors is coupled to a heterotrimeric G protein? 
Select and explain. 
A. Glycine receptor, B. GABA-B  receptor, C. Nicotinic acetylcholine receptor at myoneural junction, D. 5-HT3 receptor
B: GABA-B  receptor
Answer: B: GABA-B  receptor 
Explanation: The GABA-B receptors are metabotropic and are coupled to heterotrimeric G proteins that increase conductance in K+ channels, inhibit adenylyl cyclase, and inhibit Ca2+ influx.