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
The bitter taste is mediated by the action of 
Select and explain. 
A. Guanyl cyclase, B. G protein, C. Tyrosine kinase, D. Epithelial Na+ chain
B: G protein
Answer: B: G protein 
Explanation: Sweet- G protein coupled increased in cAMP causing closure of K+ channels.
Salt- Opening of amiloride sensitive Na+ channels
Sour- Increased intracellular H+ concentration causing closure of K+ channels
Bitter- G protein-coupled increase in intracellular Ca++ triggering neurotransmitter release.