This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: JIPMER 2019, Subject name: Physiology
[{'content': 'Phase of cardiac action potential, where calcium channels close & slow potassium channels open : \nSelect and explain. \nA. Phase I, B. Phase II, C. Phase III, D. Phase IV', 'role': 'user'}, {'content': 'Answer: C \nExplanation: In cardiac action potential Phase O - Rapid upstroke - due to fast sodium channels- Influx of Na+Phase I - Initial repolarization - fast Na channels - closePhase II - Plateau - due to calcium influx Phase III - Rapid repolarization - Calcium channels close & slow potassium channels open Phase IV - Resting membrane potential - - 90 mv', 'role': 'assistant'}]