This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Transpo Processes, Subject name: Physiology
In the sodium-calcium exchanger (NCX), the ratio of Na+ : Ca++ exchange per event is: 
Select and explain. 
A. 6:01, B. 3:01, C. 1:01, D. 1:03
B: 3:01
Answer: B: 3:01 
Explanation: NCX (sodium and calcium exchanger) is present in the myocardial fiber. It exchanges 3 Na+ with 1 Ca++. That is, 3 sodium ions are moved out of the cell for every 1 calcium ion brought in (L type Ca channels).