This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CHF, Angina Pectoris and Myocardial Infarction, Subject name: Pharmacology
Digoxin is used for treatment of congestive hea failure. It acts by inhibiting:- 
Select and explain. 
A. Na+ K+ ATPase, B. H+ K+ ATPase, C. Na+ H+ ATPase, D. Na+ K+ 2 Cl- cotranspoer
A: Na+ K+ ATPase
Answer: A: Na+ K+ ATPase 
Explanation: Digoxin acts by inhibiting Na+K+ATPase of myocardial fibres by binding to its extracellular face- Accumulation of sodium in the cardiac cell- increased intracellular calcium. This Ca2+ is shifted to sarcoplasmic reticulum with the help of SERCA for storage. Thus, during systole, entry of calcium from membrane Ca2+ channels triggers release of high amount of Ca2+ from the sarcoplasmic reticulum and result in increased contractility.