This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Special Senses, Subject name: Physiology
[{'content': 'The receptors for umami taste are specifically stimulated by: \nSelect and explain. \nA. Glutamate, B. Sucrose, C. Quinine, D. Lysyltaurine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Umami taste is due to activation of a truncated metabotropic receptor, mGluR4, in the taste buds. Glutamate in food may also activate ionotropic glutamate receptors to depolarize umami receptors. Sucrose stimulates sweet receptors; quinine activates receptors for bitter taste. Lysyl taurine is a compound that activates receptors for salty taste. Salt and sour tastes are triggered by activation of ionotropic receptors (ligand-gated ion channel) Sour, bitter, and umami tastes are triggered by activation of metabotropic receptors (GPCRs).', 'role': 'assistant'}]