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: Pharmacology
Digitalis has positive inotropic effect-by the virtue of its effect on: 
Select and explain. 
A. Na+ K+ ATPase pump, B. Na Glucose channels, C. H+K+ ATPase pump, D. Calcium Pump
A: Na+ K+ ATPase pump
Answer: A: Na+ K+ ATPase pump 
Explanation: Digitalis binds selectively to Na+ K+ATPase and inhibits this pump. 
Thus it increases intracellular Na+ and decreases extrusion of Ca2+