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': 'Staircase phenomenon (Treppe) is due to: \nSelect and explain. \nA. Increased availability of intracellular calcium, B. Synthesis of stable troponin C molecules, C. Summation, D. Tetanus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Changes\xa0in\xa0muscle strength\xa0at\xa0the\xa0onset of\xa0contraction\xa0due\xa0to\xa0repeated\xa0stimuli\xa0are\xa0known\xa0as\xa0staircase\xa0effect\xa0(Treppe). Although\xa0all\xa0the\xa0possible\xa0causes\xa0of\xa0the staircase\xa0effect\xa0are\xa0not\xa0known,\xa0 primarily by\xa0increasing\xa0calcium\xa0ions\xa0in\xa0the\xa0cytosol\xa0because\xa0of\xa0the\xa0release\xa0of\xa0more\xa0and\xa0more ions from the sarcoplasmic reticulum with\xa0each successive muscle action potential and failure\xa0of\xa0the\xa0 sarcoplasm\xa0to\xa0recapture\xa0the\xa0ions immediately.', 'role': 'assistant'}]