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
[{'content': 'Which of the following receptors is coupled to a heterotrimeric G protein? \nSelect and explain. \nA. Glycine receptor, B. GABA-B  receptor, C. Nicotinic acetylcholine receptor at myoneural junction, D. 5-HT3 receptor', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The GABA-B receptors are metabotropic and are coupled to heterotrimeric G proteins that\xa0increase conductance in K+ channels, inhibit adenylyl cyclase, and inhibit Ca2+ influx.', 'role': 'assistant'}]