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
Staircase phenomenon (Treppe) is due to: 
Select and explain. 
A. Increased availability of intracellular calcium, B. Synthesis of stable troponin C molecules, C. Summation, D. Tetanus
A: Increased availability of intracellular calcium
Answer: A: Increased availability of intracellular calcium 
Explanation: Changes in muscle strength at the onset of contraction due to repeated stimuli are known as staircase effect (Treppe). Although all the possible causes of the staircase effect are not known,  primarily by increasing calcium ions in the cytosol because of the release of more and more ions from the sarcoplasmic reticulum with each successive muscle action potential and failure of the  sarcoplasm to recapture the ions immediately.